OM617 Lacking top end/ gets hot in 5th ~ '85 CJ7 - Page 2 - PeachParts Mercedes-Benz Forum

southofantarctica · #16 02-03-2015, 09:48 PM

Mach4, I agree 100%! However for the short time that I've had it in more or less driving condition, the coolant gauge has been close enough to make sure I wasn't burning up the engine while getting things like brakes, throttle linkage and general testing done while the jeep was idling and/or short trips to the store. But know that things are getting more ironed out, I am in need of more specific information like you said.

The EGT is out of the budget until taxes are paid, and I already have the analog coolant gauge bought. The probe bottomed out when I tried to install it, so my plan is to use spacer tube to extend my probe out from the block an inch or so.

Also, boost gauge is covered as we had no idea what the engine would do we we got it started.

Thanks for the input!

funola · #17 02-03-2015, 09:58 PM

""250*" is where it stays at around town and at idle. Anything below that and the thermostat doesn't even warm up or have the system start to build pressure. When it gets "hot" it will move up past the 280 mark. Its an electric universal temp gauge. "

If the system is not building pressure when the gauge says it's 250F. I'd say your gauge is way off. Get an IR temp gun from Harbor Freight and verify your temps. They are cheap. If you can't afford one, buy it anyway and return it (tell them you don't like it or some other BS).

OM617YOTA · #18 02-03-2015, 11:10 PM

Definitely get some accurate gauges in there, you may not even have a problem.

For a mechanical gauge, I welded an NPT pipe coupler to the plug in the stock gauge location in the side of the head, spaced to give enough room for the probe. There are pics in my build thread, or I can post some tomorrow after work.

Edit: I paid $30 for my EGT gauge on Craigslist. Worth a look.

southofantarctica · #19 02-03-2015, 11:45 PM

Ok, that's what I was thinking about doing. Glad to hear that my idea should work out. I'll pop over and check your thread out.

It would be great if its not getting hot... However I don't think that'll be my luck. Seems to creep it up too much for there not to be a problem.

Yeah I tried that avenue... In all of Texas, I found a total of 3 all priced above $150.

Cadin · #20 02-03-2015, 11:55 PM

I also got an EGT cheap off of the 'List. (Boost gauge from the same fellow, cheap!)Best purchase ever; and so much peace of mind.

Even when my EGT's get warm, it doesn't influence the coolant temperature much, unless as OM617Yota notes, I'm pulling a long grade.

(FWIW: I'm running 4.11 in the rear, and I am at ~75mph @3000 rpm in 5th gear, in an FJ80 (~5200lbs) with 31' Duratrac tires. My EGT's barely break 1000F on a hill, with 16lbs of boost.)

OM617YOTA · #21 02-04-2015, 12:57 AM

Lots of infrared thermometers available relatively inexpensively.

Digital InfraRed Thermometer with Laser Sight - Random Color (-32'C~380'C/26'F~716'F) - Free Shipping - DealExtreme

southofantarctica · #22 02-04-2015, 07:04 PM

I'll keep my eyes peel in the mean time. If nothing comes up, I was looking at the one possibly with the 200-1200* reading. (1200 being the safe sustained maxim for my pistons, correct?)

EGT Analog Pyrometer Gauge + Probe Kit - Diesel Race Series DF

Cadin, the jeep should have roughly 1000lbs less than your 80.... So that gives me hope. Did you tweak your pump? I dont remember if you said in your thread.

Yota, I skimmed through your thread and couldn't find the pictures you wee talking about. Of you wouldn't mind linking them, that would be a big help.

And I even got into the car to go my me one of those temp guns back when the gauge started climbing over the 80°c on the gauge face, but touched the return hose and it was still cool so I held off on getting it. I think I'm of just going straight to the putting in a correctly reading gauge and call it good. See what that does for me.

Then advance the IP....

OM617YOTA · #23 02-04-2015, 09:54 PM

Here you go.

southofantarctica · #24 02-07-2015, 11:15 AM

Appreciate it!

mach4 · #25 02-07-2015, 11:43 AM

Quote:

Originally Posted by southofantarctica

I was looking at the [EGT gauge] with the 200-1200* reading. (1200 being the safe sustained maxim for my pistons, correct?)

I think it's actually a little higher than that. With a bone stock 617 with the pyrometers mounted 4" from the outlet of the exhaust in the tube between the manifold and turbo (I've got a Cali engine with a test pipe) I get slightly above 1250 sustained climbing a grade in the summer. So for the thousands of people running without a pyrometer that's what they're pulling - fat dumb and happy...with no apparent ill effects to the pistons or turbo. It also depends on where you take your reading i.e. before or after the turbo.

This article seems to confirm that - http://mercedesforum.com/forum/diesel-performance-49/injection-pump-fuel-adjustment-mw-m-pumps-engine-tuning-maintenance-46097/. Note it's talking about modifying fueling and boost which would produce higher EGT.

Quote:

If you skip installing a pyrometer you risk major damage to the engine and turbo from high combustion heat.
Extended WOT of more than 10-20 seconds can create combustion temperatures high enough to damage the engine. This damage is not instant, its cumulative. The longer you run hot the more damage excessive temperatures will do and it won't be obvious there is a problem until its too late. 1250*F (675*C) is a safe limit for continuous output, 1400*F (815*C) is acceptable for short intervals (under 5 seconds).

southofantarctica · #26 02-09-2015, 12:05 AM

Ok, that's where I was getting that 1200 * number from. I knew I had read it somewhere. If that's the case then I'll shoot for one that goes up to 1500* so that I'll be able to monitor the full range.

If increasing fuel makes the EGTs raise, adding boost (within reason) should lower the EGTs. Am I thinking that through properly?

mach4 · #27 02-09-2015, 12:48 AM

Quote:

Originally Posted by southofantarctica

Ok, that's where I was getting that 1200 * number from. I knew I had read it somewhere. If that's the case then I'll shoot for one that goes up to 1500* so that I'll be able to monitor the full range.

If increasing fuel makes the EGTs raise, adding boost (within reason) should lower the EGTs. Am I thinking that through properly?

In a diesel you can only increase fuel until you reach stoichometric ratio - after that all you'll get is black smoke (think tractor pulls). Adding a turbo increases the amount of air available - the more boost, the more air, and of course the more fuel you can add and the more heat produced.

So no, increasing boost increases EGTs.

A common way to decrease EGTs is water injection.

Cadin · #28 02-09-2015, 03:59 AM

Quote:

Originally Posted by southofantarctica

Cadin, the jeep should have roughly 1000lbs less than your 80.... So that gives me hope. Did you tweak your pump? I dont remember if you said in your thread.

I did tweak it a little when I had it off to check out the intermediate shaft bushing play; I think it was 1/4-1/2 of a turn on the rack limiter, I'll have to check my notes. I was trying to be ultra conservative whilst I read up on the IP's adjustment. (Om616's write up is an excellent resource.)

The ALDA is essentially deleted, and the exhaust is still the stock FJ80. Greater boost will lower EGT's as combustion becomes more complete; until you run out of fuel, then they will raise, black smoke, etc. (If I'm pulling a really steep hill, I may be @3600rpm in 2nd gear @ 35mph. I often shift @~4200 rpm if I'm climbing a grade, or getting on the freeway.)

southofantarctica · #29 02-11-2015, 11:33 AM

Ok, that it what my understanding of how to manage the EGTs. The simple version is to find a happy medium between fuel and air.

I do have OM616's write up saved for future reference when we decide to move on and start adjusting the IP.

I normally shift around 3200-3500rpms, seems to pull good until you get into overdrive. We'll see what kind of temps we have at the end of the month.

Ordered a EGT gauge today, hoping to be able to install it on the 28th. It'll be nice to actually be able to see what is happening.

winmutt · #30 02-11-2015, 12:41 PM

I bet money your timing is off.