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  #1  
Old 02-03-2017, 07:16 PM
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Does head temp measured at glow plug mean anything?

84 SD has had a slight shake at idle since I've owned it. I recently put glow plugs in because the glow light quit and the car was hard to start. New Bosch glow plugs fixed the the starting and light issues. I didn't have a reamer so didn't ream the holes.

To fix the shake, several valve adjustments, rack damper bolt new and adjusted (from the spare parts bin), rebuilt Greazzer injectors and relief valve. No compression tester.

I was playing with my IR thermometer measuring temp of the glow plug on the GP flats. Numbers 2-5 measured 158-160 * F on an engine driven to the store about 1 mile away. GP # 1 only measured 140*. FWIW, the dash coolant temp only goes to 80*C and not higher.

Is there anything else to consider than compression? I'll check temp again in the day light and am planning on checking valves again when it gets a little warmer out. What else is there in the system besides valves, rings and injector which has been replaced that might only affect 1 cylinder?

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.
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  #2  
Old 02-03-2017, 08:33 PM
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Air leaking into fuel, delivery valves, pump elements, gummed up IP, collapsed motor and transmission mounts, idle set too low.

The injector hard lines are first filled from the rearmost cylinder, so the number one cylinder hard line is the last to get filled.
A small air leak will tend to give symptoms on the first cylinder.
There should be no visible air in any of the clear hard lines.

If the shake at idle is worse after a long hard freeway run, it's probably the deliver valve seals and/or springs.

If the idle shake is the same when engine is hot or cold, it's probably a gummed up IP or collapsed motor and transmission mounts.

For a gummed up IP, I'd try running a couple of cans of Diesel Purge (or ATF) directly through the IP with an under the hood mini-tank to bypass the main fuel tank.
Get the engine good and hot right before the Diesel Purge.
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  #3  
Old 02-03-2017, 09:03 PM
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To address the question about temps at the glow plugs. One of the issues with gathering data is that if there's no baseline data to compare it's pretty hard to make much out of the numbers. We got into that all the time on our dyno engines - we could instrument pretty much anything but if you you don't know expected values you can't draw any conclusions from that data.

What you really need is temp data from a similar engine that runs perfectly so that you can compare results from your engine. I'd offer to gather that data but my engine is so modified that I don't think my data would be comparable. Maybe someone on here has similar instrumentation to what you're using and can share those measurements.

If you want to drive to coastal NC I'd be happy to run your compression with you.

Dan
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  #4  
Old 02-04-2017, 09:55 AM
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I have another SD that runs well but is not licensed. I may compare its running temp. Something is causing the lower temp on cylinder 1.
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  #5  
Old 02-04-2017, 10:20 AM
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Quote:
Originally Posted by Junkman View Post
84 SD has had a slight shake at idle since I've owned it. I recently put glow plugs in because the glow light quit and the car was hard to start. New Bosch glow plugs fixed the the starting and light issues. I didn't have a reamer so didn't ream the holes.

To fix the shake, several valve adjustments, rack damper bolt new and adjusted (from the spare parts bin), rebuilt Greazzer injectors and relief valve. No compression tester.

I was playing with my IR thermometer measuring temp of the glow plug on the GP flats. Numbers 2-5 measured 158-160 * F on an engine driven to the store about 1 mile away. GP # 1 only measured 140*. FWIW, the dash coolant temp only goes to 80*C and not higher.

Is there anything else to consider than compression? I'll check temp again in the day light and am planning on checking valves again when it gets a little warmer out. What else is there in the system besides valves, rings and injector which has been replaced that might only affect 1 cylinder?
Cylinder head temperature (CHT) has some significance when the engine is 1) air cooled, and 2) has individual heads for each cylinder, as in aircraft piston engines. Also, in that case, the CHT is of significance when the engine is under load.

In the situation posed by the OP, the engine is liquid cooled, has a common cylinder head for all cylinders, and is not under load when temperature observations are made at various points on the head.
In this situation, the exterior body of the glow plugs is an extension of the head casting itself, and reaches a temperature similar to that of that area of the head casting in which it is in contact. The observed temperatures, and the distribution of those temperatures along the length of the cylinder head, is likely more a reflection of the flow of coolant thru the block and head than any other factor.

A few words of Macbeth might apply:
"... full of sound and fury, signifying nothing."

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  #6  
Old 02-04-2017, 11:24 AM
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Do temp readings where the exhaust manifold attaches to each port corroborate lower #1 temp? Temps aren't indicative after driving a couple of miles even if the temp gauge won't go higher. Try after 20 miles when every corner should be at operating temp.

Sixto
83 300SD
98 E320 wagon
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  #7  
Old 02-04-2017, 12:12 PM
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You have new glow plugs. If they are all from the same production batch and that is a good probability. Plus if they are not the old large series loop plugs and they are not from your description.


You want a voltmeter with a mill volt reading capacity. Almost all will have this even the 5.00 specials. Get the engine warmed up. Remove the plug in glow harness. Read and make a note of all the milli volt readings and post them.


Temperature sensing with a hand held unit is perhaps best to quickly locate a really pretty bad cylinder. It is not to be trusted for many reasons.


Remember to read the glow plug harness point for each cylinders glow plug to the engine block. Or valve cover. No other ground point for the meter like the battery negative terminal can be used or the cars body shell.

With your brand new glow plugs this will show any cylinder imbalance present. It can be very, very sensitive test as well. As a general rule any differeance of .5 milli volts is considered really substantial with a well balanced set of glow plugs. On average you will read you glow plugs in the 5 to 12 milli volt range.


The handheld temperature scanning units may prove useful in the future. By removing their sensors and installing the sensor in a clip on mechanical unit. So the sensor sees only a portion of the glow plug and that is pretty much the exact same area on each glow plug. With wires extending back to the hand controller.


This would get around the issue of the glow plug being used as an electric thermocouple when testing with the milli volt method. It takes more effort in moving glow plugs around to verify what you have found. Plus the milli volt system cannot be thought accurate on older glow plugs.


Simply because as the glow plugs age they change it seems. In relationship to how many milli volts they will show in comparison to other glow plugs under the same cylinders temperature conditions.


Your post is a good one as I have been considering a way to make the reading of the cylinder temperatures simpler. You stirred my mind. Or what is left of it.


Making the sensor remote from the hand controller is about the only possible solution I can think of. Only making sure all the glow plugs under test should have approximately the same surface cleanliness. Or similar dirty surface conditions.


Perhaps we will as a group get a simpler and useful test going yet. The milli volt system was always good if you took the time to it properly. when people took shortcuts far less so.


Plus I never trusted it on an old set of plugs. Other members I can think of might have to work out the details. It may or may not have promise.


In both types of tests it is a comparison method. No actual accuracy of either the meter or the IR sensor is an issue.


The clip device that holds the Ir sensor in place should not be conductive thermally. Serious elevation of the temperature it is subject to might cause some issues with the sensor itself.


Many plastics can cope with the glow plug temperature. There still are many plastics that will degrade at 180F degrees as well though.


A nice effect if this were to work out is the IR sensor can be applied to the older series plugs as well. I have two older engines with them in cars that never see really cold driving. The milli volt system was not practical to use on them


A heavy gauge wire and a cheap meter will get me going again if one plug fails when I am out somewhere with one of those cars. I even have a spare used plug in each cars trunk as well.

Last edited by barry12345; 02-04-2017 at 01:11 PM.
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  #8  
Old 02-04-2017, 12:51 PM
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Asking from a position of ignorance, would variation in glow plug resistance correlate with variation in voltage?

Sixto
83 300SD
98 E320 wagon
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  #9  
Old 02-04-2017, 01:22 PM
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Quote:
Originally Posted by sixto View Post
Asking from a position of ignorance, would variation in glow plug resistance correlate with variation in voltage?

Sixto
83 300SD
98 E320 wagon




No ignorance there. Logical question.


Resistance is only a factor if current is flowing. On the pencil plugs you are only measuring the potential amount of voltage present produced from the different metals in temperature elevation. A simular example perhaps.


If you take a headlight bulb and attach one lead to a car battery terminal. If you read the voltage between the other battery terminal and the other headlight terminal.


You have put a high resistance into the circuit but the circuit is not complete. So you will still read the same battery voltage (potential) between the unused battery terminal and that unused terminal on the headlight bulb. The potential is there to do the work (current) but the circuit to allow it is not complete.
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  #10  
Old 02-04-2017, 01:49 PM
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Quote:
Originally Posted by Alec300SD View Post
Air leaking into fuel, delivery valves, pump elements, gummed up IP, collapsed motor and transmission mounts, idle set too low.

The injector hard lines are first filled from the rearmost cylinder, so the number one cylinder hard line is the last to get filled.
A small air leak will tend to give symptoms on the first cylinder.
There should be no visible air in any of the clear hard lines.

If the shake at idle is worse after a long hard freeway run, it's probably the deliver valve seals and/or springs.

If the idle shake is the same when engine is hot or cold, it's probably a gummed up IP or collapsed motor and transmission mounts.

For a gummed up IP, I'd try running a couple of cans of Diesel Purge (or ATF) directly through the IP with an under the hood mini-tank to bypass the main fuel tank.
Get the engine good and hot right before the Diesel Purge.


The lift pump is recharged or in these systems topped off might be a better term only once on a total rotational cycle of the injection pump.


On a fuel system in good condition this is fine. You might have an answer I have been curious about for some time. What element loads first after the top off?


I figured I might have to have a look at the crankshaft lobes in the injection pump to verify what I though. Maybe you can spare me this. I had a supposition that it was the first element from some effects I have observed. If I am wrong I will have to do a rethink about something.


I thought you would check back on this this thread and might reply. I am not trying to steal the thread. It may take the poster a little time to get back to us with some milli volt readings if he does them. Personally I think it is in his interest to get them.


I am not interested in the firing order of the engine. Just what element loads first after the lift pump tops up.
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  #11  
Old 02-04-2017, 02:20 PM
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Quote:
Originally Posted by Dan Stokes View Post
To address the question about temps at the glow plugs. One of the issues with gathering data is that if there's no baseline data to compare it's pretty hard to make much out of the numbers. We got into that all the time on our dyno engines - we could instrument pretty much anything but if you you don't know expected values you can't draw any conclusions from that data.

What you really need is temp data from a similar engine that runs perfectly so that you can compare results from your engine. I'd offer to gather that data but my engine is so modified that I don't think my data would be comparable. Maybe someone on here has similar instrumentation to what you're using and can share those measurements.

If you want to drive to coastal NC I'd be happy to run your compression with you.

Dan


Depending on what information is wanted. Most require a baseline as you suggest. In the milli volt or thermal readings on these engines. We are not trying for a standard or to meet one.


We are simply doing comparisons between existing cylinders. The closer they are to identical. The more likely the power balance is the same. Basically we are just usually seeking the cylinder or cylinders that are running cooler than the average.


Although on a rare occasion a cylinder running at a highly elevated temperature might be located. Perhaps the result of an injector with a real leakage problem.


Guessing is both expensive and frustrating. Milli volt testing done properly will lead you to the cylinder that has the issue. It will even allow you to correct the issue at times depending on what it is. It is also useful in clearing an engine of a suspected power balance issue.


It is even a servicing system that was issued a patent to a large injection equipment manufacturer. Some Japanese automotive companies have service reps that are expected to use the system at times.
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  #12  
Old 02-04-2017, 02:49 PM
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I don't think those temperature readings mean much of anything. You need to do a compression test next.
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  #13  
Old 02-04-2017, 09:02 PM
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Originally Posted by Mxfrank View Post
I don't think those temperature readings mean much of anything. You need to do a compression test next.

Yes and no. The milli volt readings on a fresh set of glow plugs from the same batch give results that indicate directions to pursue. The readings from a hand held IR gun are unreliable to say the least in my judgement as well.


Specifically that you do have a power balance situation. Or you do not. There can be some if not many issues in the fuel system where you will read good milli volts across the engine. But the idle is not good.


I can think of air getting in as one issue . Or a faulty injector etc. By and large though I do agree pretty early on the compression should be checked.


The beauty of the milli volt system it is fast and easy to do. Say for example you do a compression check first and the compression numbers are decent and fairly equal. You do not even know what cylinder or cylinders are creating the issue that is concerning you.


If the cylinder problem is not severe even loosening one injector line after another will not find it many times. So you land up back almost where you started sometimes.


It may also sound strange perhaps. It almost gives me an indication of the overall condition of the injection pump. They are old and because of some wear or other factors the milli volt readings tend to be off a little from what you might normally expect. In relation to each other overall.


We I think are getting to the point that a lot of delivery valves are getting deposits or wear either allowing poor sealing or I guess total malfunction of the system to open the injector properly.


Even if there is a problem cylinder situation. I like the other cylinders to produce about the same milli volts in relation to each other. Again and why I stopped really promoting this approach was people were starting to take serious short cuts.


A serious example is needed. A fellow years ago private messaged me. He had been following the milli volt thread. He sent his injection pump out for rebuilding.


Installed it and was not that happy with the sound of the engine. So he fine tuned all the injection pumps element adjustments to equalize all the milli volt readings.


It was a terrible thing to do and I understood that he got the ideal because we were so successful in getting any one element functioning well again for a time. Especially when we identified a cylinder as knocking.
Personally I was really surprised at the success rate.

It was no mental help to me that he could have really messed up his newly calibrated injection pump. What I believe happened because his engine ran better after his adjusting. Or no worse.


He custom matched his injection pump to existing problems like an old set of injectors. I really would have hoped he would have contacted me before he decided to do what he did.


Then there were the guys that bypassed methods of verification on old glow plugs. Tedious but required. So I thought that some damage will be occurring and let it go.


I trust it in the right hands. It can save a lot of money by reducing the spending of money where there is no indicated real need.


No grief will result by measuring a fairly new set of glow plugs milli volt output. There is an plug in glow plug harness even to facilitate it.


The IR system as mentioned modified might prove really good or not. It does remove all concerns about the glow plug being used as a voltage generating thermocouple and the different charactaristics in relation to each other as they age.


I have no time to work on this approach. It would be a great advance if a member did and it turned out useful. I do not know if it would have the sensitivity that the milli volt system has but it might. If it did it could enable a massive change. Those thermal readers are probably down to around 10.00 shipped in from China on Ebay including postage.


A warning though. The milli volt readings are the result of the temperature rise in the metal part of the glow plug in the pre chamber. There is an element in that metal end with one end grounded.


The ir sensor will only read the external temperature of the glow plug. This may be influenced too much by the local block temperature to have anywhere near the same accuracy. The milli volt system used properly has extreme accuracy. Absolutley proven.

Last edited by barry12345; 02-04-2017 at 09:23 PM.
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  #14  
Old 02-04-2017, 10:16 PM
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Well, I learned something tonight. I took a brand new out of the box GP. Put my meter on voltage, and measured across the terminal and shell at room temperature. The reading was 0. I then put the tip of the GP on my kitchen cooktop, and turned it on. Damned if the voltage reading didn't increase in proportion to temperature. It makes sense, now that I think about it, since both the steel shell of the GP and the nichrome element are exposed to the same high temperatures. Steel and nichrome have different Seebeck coefficients, so a potential is created as the part is heated. As for "new" vs "old", it shouldn't matter, since the current arises directly from the properties of the materials. For the same reason, it shouldn't be necessary to use one reference plug moved from cylinder to cylinder, as long as all the plugs are from the same manufacturer and batch. The one hitch is that carbon deposits would affect the readings.

Last edited by Mxfrank; 02-04-2017 at 11:24 PM.
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  #15  
Old 02-05-2017, 03:18 PM
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So, to be clear, measure milli volts at the glow plug connection with ground to the engine?

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.
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