Interesting running hot question
 

It seems almost immediately after swapping my injector nozzles out my 300 is running very hot. It has always run at 83 C and never higher then 90 C in stop and go with the A/C. Ever since swapping those nozzles its running at 95 and now 105 C. No overheating, it stays rock steady at 105 now but I am still very concerned. I don't think its a cooling system issue as it was so immediate and jumping the aux. fan does nothing to bring the temps down. Could the new injector nozzles cause this dramatic of a temp change?

Are you sure you didn't damage/disturb the wire running across there for the temp sensor for the gauge? Maybe its just not reading the right temp.

Its possible the temp sensor went bad, the wire is brand new along with the GP harness. I could be wrong but the engine feels like it is indeed throwing off more heat. I need to borrow one of those IR temp gauges from someone to check for sure.

Your injectors also need a couple hundred miles to "seat".
Actually, disturbing the connection for the gauge sounds like a good theory to me. You may not have been getting an accurate reading before.
To me, WHERE it runs- as long as it is in normal range and holds steady- isn't a huge concern. But, I want that gauge there to tell me if I suddenly have a problem or not- IE, suddenly pegging at hot.

I'm pretty convinced that the gauge is accurate. The wire is brand new as of 3 or 4 months ago and it is possible the sensor is going bad but I doubt it. I've spent enough time in the hot engine compartment adjusting the trans bleed valve to get a feeling for operating temp and it feels significantly hotter. It's been driven a couple hundred miles since the injectors were done and it got worse. It started running at 95-100C immediately following the injectors and now its running at 100-105C as of yesterday. I have a back up vehicle for the next week and a half (grandmothers Buick Roadmaster was running hot until I just replaced one of the cooling fans) so I would like to get this under control.

How old is your radiator? ;)

Do you notice any difference in driveability?

Meaning, is it more "sluggish". Does it require more fuel to achieve the same acceleration as before the nozzle change?

It's quite the conundrum.........I'll tell you that. There would be no way that I could fathom a nozzle change raising the engine temperature so dramatically, but, if the spray pattern of the new nozzles is off badly.......for some reason........the engine won't make power and will develop significantly higher wasted heat.

Another possibility..........the new nozzles pop at a different point than specified and the timing is retarded beause of this fact.........the driveability should noticeably suffer.

Our '83 has all new Bosio nozzles and the injectors were poptested/balanced by a professional shop, they did a sweet job, you can see how clean they are in these pics:

Temp is the same (always 82C) but it accelerates faster and has noticeably more power....

http://www.tglmarketinginc.com/mbfor...i-64220203.JPG

http://www.tglmarketinginc.com/mbfor...i-64220204.JPG

No driveability differences, although I have seen a bit more smoke now. It fixed about half of my shake at idle. The radiator looks fairly new with out any real bent fins although I don't know when it was replaced. This has been so sudden in the matter of 2 days I find it hard to believe something clogged up.

Injection timing can have a significant affect on the running temp. If the timing is too advanced then the engine can run hot. It can also melt pistons and pre-chambers in that situation.

http://i13.photobucket.com/albums/a2...ybapa/a417.jpg

Because the *actual* timing interval of the injection is a combination of the timing of the pump building pressure and *also* the breaking pressure of the injectors, if you change the breaking pressure of the injector it has a direct affect on the actual timing of the injection interval. If pop pressure is lowered timing is advanced and if it is raised it is retarded as the pump will take longer to build the higher pressure.

Did you check the breaking pressures of the injectors after the nozzles were installed? If not then I would do so for sure, especially because of the running hot situation.

Andrew

Yes, I was thinking along the same line. However, you mentioned a low pop pressure causing advanced timing and additional heat because of this.

This makes very good sense because the driveability would not suffer measurably, but the additional heat would be quite noticeable.

I strongly concur with the need to pull the injectors and have the pop pressures checked and adjusted.

This was my general thought and I wanted some back up opinions. Thats what the forums are for. Anyone know of a shop that will do them? I don't know of any locally and whunter is looking to no avail so far.

There's about 10 or more diesel injection shops here in Grand Rapids, the one we went to completely did all of the injectors for $98 and had it done in less than 7 hours after we dropped them off.

Come on up to GR and use one of our shops! :D

Roy doesn't know of a local shop to test injectors?:eek:

I agree! Thats a huge metro area, how can there be no diesel shops?!? :confused: There were shops all over the place when we drove over to Roy's.....seems weird that none would do injection.

He had a list on one of his computers before it crashed.

There are a couple of oddities to that scenario. It is very untypical that changing nozzles would lower breaking pressures. Typically as the nozzles wear the pressure drops and so timing is advanced. Usually replacing the nozzles will bring the pressure back up. The concern is that there was a dimentional difference between the old nozzles and new. Regardless, they should be balanced together. You'll be glad you did.

The other oddity is the smoke. Overly advancing the timing will typically reduce smoke rather than increase it. Still, the symptom of overheating corresponding to nozzle swapping really begs for checking the pop pressures just to be on the safe side.

FYI the piston I pictured was from a VW 1.6TD engine that never saw EGT's over 900°F. EGT gauge and probe were new as was the piston 3000 miles previous.

Andrew

How would it be possible to lose the piston due to heat if the EGT never climbed above 900°F? This would argue that an EGT gauge is not an accurate predictor of safe engine operation. I have a suspicion that the gauge was not mounted in the proper location...........unless you have another theory??

You can't destroy a piston with 900°F. combustion temperatures.

Combustion temperatures are not exhaust gas temperatures. Certainly the two are related, but exhaust gas temperatures are after primary combustion. With injection timing overly advanced fuel still has additional time to burn completely and so the gasses out the exhaust will have cooled down. The actual combustion temps were certainly obviously higher than 900° but EGT's were not. The only untoward symptom was "hotter than normal" coolant temps until it melted down.

Andrew

If you are measuring EGT's right at the exhaust port, the exhaust gases have less than .04 seconds to evacuate the cylinder at 3000 rpm.

How can they cool significantly in this timespan?

Sorry, I don't see it.

Anyway Tomj is going to check and balance them for $10 a piece. We shall see what comes of it.

I think "cool significantly" is the question and Brian's response of "no, they can't" may or may not be correct (as if there were any other answers, lol). As soon as the exhaust valve begins to open the gas expands and a relatively expanded gas is a cooler gas. So, if 40 milliseconds corresponds to the duration for which the exhaust gasses have mostly evacuated the cylinder then I'm guessing that decrease in gas pressure and subsequent drop in temperature is quite realistic.
I did a google search for "Ideal Gas Law". This equality is:
PV=nRT
Where:
P = Pressure
V = Volume
n = moles of gas contained in the Volume, not dependent on whether that Volume is dynamically changing, as it is in our present discusstion (the quantity of gas, exclusive of the Temperature, Volume it is contain in, or the Pressures seen in the cylinder/exhaust port (in this case)
R = a constant
T = temperature (our main interest here so we know how fast the gasses cool at the exhaust port; actually at a particular location and a particular time)

So, in our discussion, we can come close in estimating the value of the "n", how much gas is present (measured in moles which is derived from the precise number of gas molecules). We know with some precision the value of the constant "R". We can calculate the Volume of interest. Not so in practice, but in theory we can calculate the Volume to some precision, but we have no disagreement that as exhaust gasses are exiting and the piston is in the exhaust stroke that the Volume is changing (yes, the volume of the cylinder is decreasing, but by opening the exhaust valve we've gained some volume in the exhaust port; but, by placing a sharp value on the Time range over which we measure gas Temperature, we can get a fair estimate of the actual change in volume, and I assume the decrease in cylinder volume while adding the relevant exhaust port volume corresponds to a decrease in Volume at the end of the exhaust stroke. A temperature probe at some point of interest, say at the interface of the cylinder with the exhasust port can be implemented. We know Pressure is dropping because the exhaust valve is open. So, now back to:
PV=nRT
For arguments sake we can drop the product "n times R", as they are constants and don't change relative relationships (though I lie a little bit because "n" has decreased somewhat. Now we still have a meaningful, but not exact, workable description of the relationship between P,V and T:
PV=T
In our example, or problem, we can open an exhaust valve, which yields a drop in Pressure. If we are in the exhaust stroke measured across the time interval of 40 milliseconds at 3000 rpm in Brian's example, we have a drop in Pressure. So, With both P and V decreasing we see a drop in gas Temperature whose actual value is determined by the product of Pressure and Volume.
Setting P and V to set values, so that their product yields a particular Temperature is telling. By this I mean we can increase the V while decreasing P in such a manner as to still have a certain unchanging Temperature.
So, getting back to the original question of whether gas Temperatures can drop so rapidly over 40 milliseconds at 3000 rpm, I assume Brian meant near the top of the exhaust stroke, where we have a radical drop in Pressure relative to the Combustion Stroke, we have a change in Volume that has some additive and some subtractive components, but if we just assume Volume consists of cylinder volume and some finite space in the exhaust port, but excluding the manifold, then we have a radical decrease in Volume.
So, P&V drop.
Since Temperature is the product of the two, it drops.
But, Brian wisely uses "significantly". I think it fair for me to plug in some aribitrary starting values, though recognizing that this arbitrariness could change "significantly" to "insignificantly", though I think I can be safe.
At BDC of the power stroke:
P = 10 (in arbitrary units of pressure measurement)
V= 50(arbitrary units)
Therefore: Temperature = 500 (arbitrary units)
At BDC plus some arbitrary degrees up the exhaust stroke:
P=2 (at least a reduction from 10)
V= 30 (at least a reductiion from 50)
Therefore: Temperature = 60 (arbitrary units)
As we reach the top of the exhaust stroke, dependent on cam duration and lift, P&V have plummeted.
I apologize for not taking the time to come up with realistic P,V,T,m,R metrics but the relations hold. I think if one had more precise values and units of measures one would see very significant declines in EGT over the 40 milliseconds of the exhaust stroke at 3000 rpm.
One other quick example. Consider you have a can of aerosol for cleaning circuit boards or keyboards, etc. The can is new and unused and has been in your house at a constant temperature so that the can & gas it contains are at room temperature. Now, spray a bit of the gas from the aerosol and either measure with a precise instrument or your finger. In both, you will see a very large drop in Temperature. This is because the Volume in which the gas is held now includes the Volume into which the gas has expanded over a set time period has Increased and the Pressure has decreased. At first glance, V rising, while P drops, could result in Temperature either increasing or decreasing. But, in practice, it just so happens the drop in Pressure is much greater than the increase in gas-filled Volume, so we see a drop in Temperature.

I agree completely with this analysis and definitely agree that there is a drop in temperature between the power and exhaust strokes.

My question concerns the generally acceptable temperature of 1200°F. as the practical limit for EGT's.

Here we have a fellow who melted a piston with an EGT of 900°F.

We make the assumption that on a properly running engine, with an exhaust temperature of 1200°F. will safely survive with a higher combustion temperature on the power stroke........say 1500°F.......just as a guess.

Now we have to really make a judgment whether the power stroke of his engine was above 1500°F. when the exhaust temperature was 900°F.

That's the part that seems incredible.

Ahh, I see now, given an EGT of 900F, it seems unlikely that the combustion temp was as high as 1500, as this is outside the range of generally observed differences in combustion temps versus EGT. Let me ask a question. In a diesel without a precombustion chamber and a bad spray pattern of the injector, say it's a narrow stream versus a proper pattern and that stream is directly hitting the piston at the same spot, would that diesel combusting in a point-like manner, would that account for a melted piston (or would the diesel tend to both cool the spot it hits and heat the spot it hits resulting in, say no temps to account for melting) while overall (average) combustion temp is mulch less than 1500F with and EGT of 900F, the differences in the two temps and the subsequent piston burning now looking more realistic? I don't recall at the moment if it was in this thread where the melting was at the edge of the piston (I remember seeing an image of a melted piston somewhere, making it's way to the first compression ring). If the melting is at the edge of the piston obviously my point doesn't even apply here. A second question I have is, if the piston is heavily coated with deposits would this cause these deposits to transfer enough heat to the piston, with the deposits also serving as an insulator, to allow the temp the piston sees at those coated spots to stay very high relative to what combustion temps and exhaust temps are, such as to result as piston melting or burnthrough? I see what you mean to say it seems an incredible scenario for piston melting with an acceptable power stroke temp of 1500F and with an EGT of 900F, especially since both are more flash-like temps than sustained temps. I know a gasoline engine can produce flash-temps high enough to melt a cast iron head, but since it exists so briefly, this heat makes its way to the coolant or exhaust port or radiative heat from the engine itself.

I think that this is a very realistic scenario. If the fuel impacts the piston at a specific location in a liquid form........poorly atomized........the resulting temperature at that location may be too great for the piston to withstand.


But, the claim was that the piston suffered this failure from advanced IP timing.

So, I remain skeptical.

I see. Well, if the heat that destroyed the piston was from advanced IP timing, whether it be the IP was too advanced, or the injectors sprayed at a lower pressure than they should have, so that is the question then? Say the injector pops way too early, now this would result in the beginning of fuel ignition occuring at the earliest possible time as compression pressure builds. So, now it would seem too much of the power of ignition is occuring BTDC, so this power working against the piston is lost as heat to the coolant and to the piston, but, as you say, there should be much less to no visible exhaust smoke. This makes me wonder if this piston didn't have severe problems prior to changing the nozzles. The resultant higher combustion temperatures finished the piston off that had already been partially burned. As regards the original post that coolant temps climbed around 20 degrees C could be due to the scenario I layed out above or the injection timing is right where it should be and he is getting more complete fuel burning from the improved spray pattern and timing and the temp guage had been giving readings that were off to the high side before, so now the engine coolant is at normal temp of say 90C, but is reading high (as it always has) causing the concern.

If we had higher combustion temperatures that finished the piston off, and they were not localized on the piston, we can safely assume that the exhaust temperature had to be greater than 900°F.............true??

i have nothing to contribute to the main discussion, but is the egt sensor in the exhaust after the collection point of the individual exhaust ports? if so it seems to me that the 900 degrees represents an average of the cylinder temps and the one in which the piston melted might be a lot higher.

also if it were caused by advanced timing wouldnt all the pistons look like that?

tom w

That's why it makes no sense to me...............

now there is that scenario in which the individual cylinder's timing can be adjusted at the top of the ip...

tom w

earlier it was said the pop pressure can change the timing as well for an individual cylinder.

I actually wondered about that when he showed us stuff on his laptop.....I thought "wow, he has a lot on his laptop, I wonder if he backs that all up...." :D

Guess not.......


I have all of the data that I use stored on two servers that mirror each other....needless to say, I'll never loose a file unless this plot of land is swallowed by the earth. ;)

Back on this subject, our '83 still idles exceedingly rough, even with the bosio nozzles, would this be a timing issue? We know that the engine has about 2-3 degs of stretch on the timing chain, and its last valve adjustment was probably 12-13k ago. Vibration at idle has recently (within the last few k) gotten a lot worse. Anyone have any suggesstions as to what this might be? Oh, and when in drive or reverse (especially drive) it feels like the engine is stumbling, kindof a "bump....bump....bump...." feeling in the already massive amount of vibration. As sooon as you press the pedal it goes away, and when I was messing with the idle, I set it around 900-950 and put it in drive, and the vibration and bumping feeling went away as far as I could tell, but I could also tell it was idling waaay high, a lot higher than my '82 does, and that one is silky smooth at idle. This stuff has all started happening very recently, so I don't get it. New nozzles, balanced/pop tested, the works, and it also has essentially 0 blowby at all, we started this beast at 12 deg's F with TWO working glowplugs before (50 seconds of cranking) and it started. With all 5 plugs it will start at 0 degrees in about 4-5 cranks. Thats whats so odd, it starts so well in the cold, but idles soooo rough. Why?!

I know you have said yours shakes/idles rough too, maybe its a similar cause? His can't shake though, it seems as if the engine is bolted to the frame of the car, but its on the normal motor mounts. Rev'ing it, it won't "lean" like mine does, and turning it off it barely moves by itself, it just shakes the entire car. Seems like its in there too tight, if thats possible.I know if I grab my engine's valve cover I can rock it back and forth an inch or so, his engine does not move, at all, it moves the car. Seems very strange....

I apologize for inadvertently hijacking this thread, but would like to respond to some of the other posts. That was the most severely damaged piston along with one other that was similar but not quite as badly melted. The other two were somewhat damaged but far more minorly. The two injectors for the two damaged sylinders did pop at somewhat lower pressures and spray patterns were slightly worse, but not dramatically. Yes the probe was immediately after the turbocharger and so add 250°F for a pre-turbine measurement of 1150°F.
With regard to EGT's of advanced timing being cooler here is my understanding. If the injection interval is advanced primary combustion will occur more on the upstroke developing intense heat as the burning gasses are compressed. Simultaneously more heat is passed to the cooling system as the head and upper cylinders are hotter. Then as the piston is pushed downward the gasses cool rapidly due to the expansion of the chamber and the more complete combustion of the fuel. If fuel is still being burned in the exhaust then the EGT's will be significantly higher than if the fuel is more completely burned. Therefore, advanced injection timing results in both elevated peak combustion chamber temps and lowered EGT's. A very frightening combo. Go ahead, give it a try and report back your results. How about 30° BTDC? Or if you don't have as much belief in your argument that advanced timing does not lower EGT's while raising peak combustion temps, then retard your timing to 15° BTDC and check out the EGT gauge. I am quite sure you'll see it elevated.

Andrew

The position of the probe now begins to make some sense. The temperatures at the ports could have been well on there way to 1200°F. The damage to more than one piston also answers some additional questions.

I fully agree that retarded timing will cause increased EGT's, but the concept of reduced EGT's due to advanced timing remains difficult to grasp. If the combustion temperatures are higher.......for all the reasons mentioned.......the exhaust temperatures at the exhaust ports should also be higher. I simply can't envision a the scenario where an elevated combustion temperature can dispose of all that excess heat into the cooling system in a very short period of time and result in a lower exhaust temperature.

However, I've never tested it.......so........I reserve the right to be wrong.;)

Rack damper bolt questionable for the bad idle? Since you have two cars a temporary swap would eliminate it as a possibility at no cost. Check the archives to see if symptomatically a marginal one can create this much disturbance or vibration at idle. As for the gentleman with the overheating or higher operation temperatures since change of nozzles. Again the only difinative answer might be substitution with a known pretty good set of other used injectors. That is of course if nothing is learnt from your new ones that are out being pop tested. But you are fundementally right. You seem to have created a lot more heat to get rid of somehow with the new nozzles. Hopefully the pop pressure test will indicate what it is. Another thought is perhaps the fellow pop testing your injectors might loan out a known good set if the problem remains with your present ones recalibrated. You may have to make positive that they are the absolute cause shortly.

now for pawosd, it seems possible to me that your car might have one cylinder that the timing is too advanced on. there is a long thread about this from about a year ago. i believe it may have been larry bible who experienced it.

at the outlet of the ip the threaded nozzles that the pipes bolt to are actually individually adjustable. and if one is mal adjusted it will fire too soon (or late) and cause very rough running. dont monkey areound with them though until you completely understand what you are doing as it is very easy to cause problems and not easy to straighten them out.

tom w

Roughness in idle. One approach is to just read the mili volt output of your glow plugs and if say one plug is signifigantly lower investigate that cylinder in a systematic way. First swap glow plugs with one that appeared to be normal to make sure it is really reading low on that cylinder. Then swap the injector in that cylinder and see if milli volts come up. If not check valve settings again. If they are good then time for compression check of that cylinder. If that is ok then it may indicate pump problem but most times you will locate and fix the individual cylinder problem before that or the cause is indicated if not practical to repair. Now if milli volt readings of plugs are all close during my initial reading of the plugs I would check the primary pump to engine timing and cam for correction. That is because the milli volt test is indicating simular strength power strokes are occuring in each cylinder. That of course being the source of a smooth idle if the principal timing etc is accurate. Bypassing all the other steps and going back only if the pump/cam setting does not clear it. You cannot loose by doing a fundemental tuneup anyways as it maximises performance and milage, cold start the whole thing so to speak. If all the above does not lead you to where you want to be there are further tests. Generally if I do not really know what is wrong with any engine many times it is revealed by just doing the basic tune up or at least many times the real fault will be indicated during the process. Guessing is terribly non productive and time wasting without a lot of daily experience.

Brian says: "I simply can't envision a the scenario where an elevated combustion temperature can dispose of all that excess heat into the cooling system in a very short period of time and result in a lower exhaust temperature."

That certainly seems to be the question as to how much of that heat can go into coolant or be radiated by the block in the time frames we're looking at. Looking at heat as work and too advanced injection using more of that heat to resist the piston on the compression stroke, it might be true. I'd sure like to know the answer to that.

Here is a scenario I've been thinking about that might explain the piston burning, the larger ratio of "Combustion Temps / EGT's".
Imagine first, for reasons unknown, that we have a good spray pattern, but due to weak injectors, or the IP being too advanced. So, our nice fuel spray occurs too far advanced, so, the initial compression induced burning begins at multiple sites at the periphery of the cloud (which, I believe it does), then, as is normal, radiative heat from the initial compression burn sites ignites the rest of the fuel. So, the pressures and temps are much higher for a longer duration before the piston reaches TDC. We see in the image of the piston that the melting seems predominant at the periphery of the piston, which is a very normal thing as edges have more heat to move and it is a slower process. As background, I don't know how many compression rings this piston has, for arguments sake let's say two compression rings and one oil scraper. The compression rings revolve around the piston not in a uni-directional fashion at from 3 to 6 rpm, but at a rate of 3 to 6 rpm, but as the ring gaps begin to near each other pressure is built up by the first gasses passing the end gap of the ring, over the first land making it's way to the gap of the 2nd compression ring pushing both in the opposite direction relative to each other, back & forth across these 180 degrees. Now, this initial problem of way higher than designed pressures & temps during the compression stroke begins a partial melt of the edge of the piston, eventually some of this melt making it's way to the end gap of the 1st compression ring and filling it. Continued partial melt enters the end gap gradually pushing the first ring tighter & tighter against the cylinder wall. Now we have that increased heat from friction, plus we've blocked the nominal amount of gas that normally get's around both both compression rings. Eventually the 2nd compression ring make's it's way so that it's end gap lines up with the now non-existent gap of the first ring. Heat is greater there because the initial fit interference at the frozen gap prevents any up & down movement, so the 2nd compression ring now locks up, with the land between the two rings expanded by the heat locking it up. So, now we have both rings locked exerting greater pressure on the cylinder wall and concomitant heat build up. The initial problem of an early injection, prior to the sealing, whether partial or complete, overheats the oil scrape ring resulting in either partial lockup, but whatever, it now doesn't scrape the hot oil well, which removal helped to keep cylinder wall & piston temps down. At this point we have a troublesome environment in progress, with more and more of the piston at the initial melt spot having nubs and good piston top/skirt edge burning. Maybe some to the same fate of the initial burn spot and the rest being ejected to the exhaust port. As material is lost from piston this lowers compression by increasing the volume normally seen at TDC, perhaps resulting in the increased smoking & the lowered EGT, while maintaining the higher peak combustion temps because the hot piston is still igniting the cloud too early due to hot spots, even though overall minimum cylinder volume has increased. Also, if the early or later piston disintegration that I hypothesized above is true, the oil scraper is not removing cylinder wall oil as it should resulting in higher temperatures. So, yes, we do get some of the excess temp gone from wall to coolant jacket, but we also have the locked rings on the piston, deficient oil scraping, and I surmise that the piston itself transfers much heat from piston top and skirt, with poor heat transfer from skirt to oil that is normally making it's way back to the oil pan. In my guess here I am saying that we're seeing combustion temps way above normal, but much of the energy has been transferred too early contributing to higher pre-TDC temps & pressures than is normal. Yet, if the EGT's are correct, where has all the heat gone from the abnormally high peak combustion temperature? Perhaps our piston/cylinder interface can transfer a lot of this heat (it doe's have more time to do so). I'm guessing, and here I just can't visualize or intuit the physics, the way advanced peak pressure and temperature is losing it's energy partly in a normal fashion via the cylinder wall and what the head absorbs, but I would think the majority of the heat is lost through friction not only on the compression stroke, but also on the power and exhaust strokes due to locked up rings, whether complete or partial lockup, so the EGT's are normal or relatively okay as this is just a gas temp we're looking at & a good deal of the gas partial pressure energy dissipated through the piston and cyl wall much before it should have relative to TDC. I realize I can't have it both ways as regards an increase in exhaust smoke, though I'm not sure if we're talking about fuel or oil being the main component. By both ways I mean I can't say the compression rings are locked tighter to the cyl walls and less oil is making it's way past the oil scraper, and we're seeing increased exhaust smoke from either oil or fuel. though perhaps there is some balance of these processes that allows my argument to have it's cake and eat it too. My argument says we're seeing rather complete burning of fuel, more so than normal, unless normal means complete burning; so, I stick with the scenario of combustion heat, per se, exclusive of all the frictional heat, having the additional time to cool by heat transfer by the time we're on the exhaust stroke at that point where maximal EGT are normally noted. My previous post of a poor, streamlike spray pattern on a single spot of the piston most certainly wouldn't be at the interface of piston top and skirt. So, I guess on the relatively low EGT's, with all the variables I've thrown into this, I would have to say that early combustion from beginning to complete is what dominates & EGT's are low because combustion is complete way too early, much of the pressure, hence heat, is lost as described previously. The fuel:air mix has a defined maximum pressure/heat it can create. I've said by a larger percentage of that pressure/heat working against the piston as it travels towards TDC is why we see relatively low EGT's, while burning pistons with relatively high combustion temps. I don't know. I wish I did. This just seems such a problem that reveals much, if understood, of both normal & abnormal diesel function that I wish I knew if my guesses are even partially on track.

Yup having Tomj balance my set fixed the temp problem. It runs back at its normal steady 83C, well it gets up to 95 when traveling around 4000 rpm on the expressway in 4th gear. ;)

The Bosio nozzles are not all that people are making the out to be. They lack the pre-ignition hole which causes noise and a little roughness. But the machine quality is better then the Indian nozzles.

Yes, perhaps. Yet, after the higher combustion temps finished the pistons and/or rings off, we now have lower combustion temps due to the loss in pressure during the compression and power stroke. So, after the damage we have lower EGT's. I'd refer to my long winded theory as to how we got very increased combustion temps with lower EGT's as a function of the presumed advanced IP Timing. Now, even after the piston/ring damage the damaged portions served as hot spots to effectively ignite all the fuel & we see no exhaust smoke. I think (I guess) that previously described faults that result in an early start of burn BTDC could very well have much of this heat removed from the cylinder volume resulting in EGT's lower than 900F (even if flash combustion temps are as high as 1500F. I think the concept of "flash temps" is important and we need to measure the average peak temp over a time period, say one half of one degree. In old Detroit Iron engines of the 60's, say the 426 Hemi or the earlier 413 Stage 3 Max Wedge, combustion temps peaked at around 4000F, hot enough to melt the cast iron head, but the key is that the 4000F is a flash temperature seen for around one millisecond or less, so no melting, just a lot of heat transfer to the block, out the exhaust or pushing the piston down the power stroke.

I the idle problem solved by balancing the injectors too?