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'76 1300L,HE351CW,H15P Winches,Konis,Hydraulics,All Gears,10mm Plungers,Aftercooler,Lots of Littles
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Discussion Starter · #1 ·
So after reading other several posts I want to ask:

Why is 1200-1300F the accepted safe max for EGT temps?

Aluminum melts around 1125F depending on the alloy (1125F is the softening temp for 6061). Granted there is going to be some heat loss from the piston to the cylinder during the exhaust stroke and EGT does not reflect the combustion temp, but would it not be safer to hold egts down to 1125 or so on turned up engines?

Just a Saturday night musing, but thought I would put it out there...

C.
 

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85' U1300L Holset Turbo VA A/C, 66' Propane 404.1 rock mog, 1975 416 Doka, G500, Volvo C303
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Well, max safe EGT's have been in debate for a long time. Some people say 1500 is ok, some wont exceed 1100. 1200-1300 have been generally accepted to be the safe point, not sure why exactly but many claim thats when the valves start to overheat and anything higher will melt the valves. I would wager that 1100 is about right for an OM352 without oil squirters, and maybe 1200ish would be right for an engine with squirters. This is solely based on the fact that the pistons get a lot more cooling.

I ran an OM617A for a long time at 1200ish max and it was solid. So there is some trueth to the 1200-1300 EGT range. I might lower my max EGT once I get my engine back together, but I am not sure just yet especially since I plan on adding squirters.
 

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85' U1300L Holset Turbo VA A/C, 66' Propane 404.1 rock mog, 1975 416 Doka, G500, Volvo C303
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Well, since some OM352's came in a version with a turbo and no squirters, there are potentially a few flaws with that info..
 

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'76 1300L,HE351CW,H15P Winches,Konis,Hydraulics,All Gears,10mm Plungers,Aftercooler,Lots of Littles
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Discussion Starter · #5 · (Edited)
I agree with KC, the Unimog Forever page on this topic is frequently cited but contains very little real information. At best it is mildly informative. With no fueling changes a Turbo will lower your EGTs and in some measure be easier on the engine (higher cylinder pressures aside).

I think the real issue with piston temp is long runs where combustion temps overcome whatever cooling is there. So with squirters you have more cooling so you can overcome this longer. My only real point in posting this to start was just to point out that 1100-1150F is a LOT safe from melting that the 1200-1300F we have all heard from various sources.

I am not sure how much power difference there is in the 100-150F EGT increase, but I am sure that it is not enough to make a UNIMOG "fast". I will stay a little lower, and a little slower.

C.
 

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Unimog U1250
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I have read the aforementioned site, as with most things on the internet - armchair experts are quick to give advice about something they might not know much about. I don't see a pedigree or a lot of tech talk from MB or a turbo manufacturer on the site at all. I think the no squirters issue is one of them. MB put them in the higher output versions of the OM352A for a reason - now whether that was a solution for using a non-waste gated turbo, to allow the fueling and boost to be increased to about 1200 deg without melting the pistons, but they would surely have only have done it because it was necessary.

In regards the safe EGT's - has anyone ever measured the EGT's of a "stock" OM352A with 125hp compared to the "stock" OM352A with 170hp. Apart from the swirters and the necessary increased oil flow from the pump - what are the difference between the two - are the pistons different? (more rings etc) Is the head different? - does anyone know?

My understanding of the primitive fuel system on my OM352A is that it delivers an amount of fuel, depending on the pedal position, to hold a certain rpm. So in theory, to hold the desired rpm at a high load, the pump would deliver so much fuel it would go over the 1200 deg mark. Now that is limited by the overall capacity of the fuel pump and how max fuel delivered is adjusted. Since the turbo is not wastegated - the max boost pressure - which is really the amount of air crammed into the engine, is also linked the amount of fuel pumped into the engine, so if you increase the fuelling, you also increase the boost (and the air flow) and hence the combination of the two give you more hp, but you will have to be a lot closer to the 1200 deg mark - hence the need for squirters.

Now if my logic is right on my 125hp OM352A - if I change the turbo to a modern and efficient waste gated turbo with more flow capacity and now control the boost via a waste gate. If I have sized the turbo correctly to run more boost at lower rpm than the OEM turbo, I should be able to run higher boost throughout the rev range and thus increased air flow that gives the same hp increase as an 170hp OM352A but with fuel ratio closer to the magic 22.1 that results in lower egt's and hence not need any squirters to stop the pistons from melting.
 

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4Sale: 230G, U1200 Ag, 1017A, lots of MB cars, Volvo c303, 416 raildoka, LR D110 TDi
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Ian,

As far as the differences between the 125hp and 170hp versons of the OM352A, The main differences are the injection pump (the plungers are bigger, although I don't remember the measurement size), and the injectors/nossles. Depending on the version of the 170hp engine, some of them had 16:1 compression, and others had 17:1 compression, so evidently some had the same pistons as the 125hp version, and others had different ones. I think I remember reading somewhere that the camshaft is different in engines over 150hp.

Cheers,
Ben
 

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Now if my logic is right on my 125hp OM352A - if I change the turbo to a modern and efficient waste gated turbo with more flow capacity and now control the boost via a waste gate. If I have sized the turbo correctly to run more boost at lower rpm than the OEM turbo, I should be able to run higher boost throughout the rev range and thus increased air flow that gives the same hp increase as an 170hp OM352A but with fuel ratio closer to the magic 22.1 that results in lower egt's and hence not need any squirters to stop the pistons from melting.
You can run higher boost through the rev range, but know the turbos size to run more boost at lower rpms will ultimately effect your top end. The charge will be warmer so you will have to have good charge cooling to help keep your IAT's down.

Most the time we tune our gas motors to run peak boost mid rev range of the turbo, then trickle it down midway to redline. Saves your motor and keeps the charge temps in check so less det etc.

Has anyone tried to adapt a variable vane turbo onto one of these yet? The mercedes sprinters have them for a parts reference.
 

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85' U1300L Holset Turbo VA A/C, 66' Propane 404.1 rock mog, 1975 416 Doka, G500, Volvo C303
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om352 has 4 and 5 ring pistons depending on variant.

the om352A has 3 and 4 ring pistons depending on variant.

Waste gated turbos create higher EGT'S at max RPM due to there constrictive nature.

You can create far lower EGT's just by adding a turbo without increasing fuel, and this will increase power. Then you slowly turn up the fuel until your max desired EGT is found. But to do this, you must be at max load as well. This of course is a very simple way to explain it.

I believe that because there is zero piston cooling, that the wrist pin and piston skirt heat up and expand enough to increase friction and melt the skirts. I was running 1200 degree egt's with zero damage to my Piston heads. Only the skirt was damaged. If my failure was from EGT's, I would have had a hole in a piston or some visible damage.

Almost everyone I have talked to that has put an EGT on their stock 416's, report shockingly high EGT's are attainable and most change their driving habits because of it.
 

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The first things to do to be able to get accurate information is to homologate/consider the variants:
1. Engine type (366 or 352) as longer travel will have a higher initial temps than a shorter piston travel one.
2. Whether or not there is piston cooling thru oil squirters
3. Measurement point location
4. Actual brand and type of gauge (accuracy, linearity, response time)

It is my experience that you can run for hours at 1250F on a 366 as measured right before the turbo with an Autometer phantom EGT.
The pistons will drag on the cylinders at higher temps as aluminum expands at a higher rate than iron. I know that from personal experience. Piston #6 will be the worst, then #5. I did not damage pistons 1 thru 4.
Once you let the engine cool down it will run normallly but it will burn oil.

The EGT problem will be way more evident at altitude but ultimately you can ruin your engine even at sea level if, say, you get distracted by a phone call exactly when you will go up on a steep incline...

Saludos
 

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Roberto is calling it like it is.
Several years ago I melted a non piston cooled 352A at 1276F measured after the KKK turbo. The temp prior the turbo was probably close to 1600F It didn't take but 60-100 seconds after hitting 1200F to then hit 1276F then whamo!
This was at around 9000foot elev.
#5 and#6 Ghandi
C.O.R.E.
 

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Discussion Starter · #12 ·
Jay brings up a good point. Keep your EGT probe pre turbo. Putting it post turbo does not provide the same level of information. I would want my post turbo EGTs to be below 800 for sure, and probably more like 700. But again, the numbers mean a lot less when the probe is there.

C.
 

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Yep, using pre turbo temps on a post turbo EGT probe location is one of the biggest mistakes newbies make when working on diesels.

Both places have there merits, but the only one that is relevant is the pre turbo.
 

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Jay brings up a good point. Keep your EGT probe pre turbo. Putting it post turbo does not provide the same level of information. I would want my post turbo EGTs to be below 800 for sure, and probably more like 700. But again, the numbers mean a lot less when the probe is there.

C.
Agreed that the EGT probe must be upstream of the turbine wheel. The pressure drop across the turbine section is not a constant, so the delta temp will also not be constant. Downstream temp is useless data.
 

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On the pre and post,has anyone ran sensors in both locations to see the temp drop on the factory kkk?
The large turbine housing on these units should shed more heat than the smaller wastegated units,but the increase in the back pressure w/ the smaller housing raise the pre temps as well. The general rule has always been a 300F drop.
One of our 1250's w/ the wastegated units is already set up for the two positions pre and post, just haven't made it a priority to rig up the to probes yet.

On factory diesel equipment it used to be pretty standard to run the probe post turbo.
The manufactures had all the data for temp drop across the exhaust sys.
Rob had a 300HP test Cummins w/14 probes hanging out of it. X2/port X1pre X1post turbo to help determine this info.

C.O.R.E.
 

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Just out of curiosity, how many factory road going vehicles have you seen with "factory" gauges aside from big rigs.

Also, J couplers that could handle higher egt's used to be expensive. So a post probe was more cost effective. So they would use pre and post at the factory to determine a standard for the post sensor.

A post sensor is the last item you need in a modded setup and is useless with out pre data. And the old 300 degree thing would be an urban legend. To many variables to make a statement like that.
 

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Dude relax, I'm pretty much agreeing w/everything you are saying.
I don't know of any light duty diesel anything w/ a factory EGT. I'm talking about Farm and heavy equipment.
I don't recall much of a price difference on probes that could handle 2000F as apposed to a lesser though.
The hole 300F drop urban legend is something that I would like to verify instead of just dismissing it. We still get conservative customers that would like the probe mounted post turbo for fear of the probe possibly failing and blowing through the turbine.

One of our U2450'sin the late 90's had a crew working w/ it that cost us around a $15,000/day just to show up. When I described the 2 options on what we where doing for the EGT on this unit,the boss was very clear that it would be mounted post turbo.
We also have a couple global trekking customers that fight w/ me to mount it post turbo as well, for fear of failure far overseas and killing the turbine.

We usually mount our probe to catch the exhaust out of #s4,5,&6 since #5&6 are usually the first to fail.

C.O.R.E.
 

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Sorry if you read that wrong, just asking a legitimate question or two. Questions like that set a better base line for what your talking about specifically. Most commercial diesels run at far lower temps because they last longer at these temps.

Prices even today vary for high temp exposed element probes. There have been some definitive increases in performance of Couplers in the last 10+ years. Much of this is due to the increased demand for performance diesel. And EGT failure was common back in the day.

I have a hand held thermocouple in my tool box that cost over 1K back in 99'. A similar unit today would run a whopping $200.

Sounds like you have some educating to do with your customers. The current possibility of an EGT J coupler probe failing in a manner that would release debris to damage the turbine are virtually zero. Plus a toasted turbine doesn't mean dead truck. Soooooo.....
 

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PS Jason.. I dont have a KKK, but I will weld in a bung post turbo when I get my engine back together. Its always fun to geek out with to much data.
 

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I seem to recall the Cummins crowd sees about 500-600 degrees difference in EGT post v pre. This is AVERAGE temperature - I suspect peak temp delta is much greater.

You don't see EGT indicators in many factory "personal transportation" vehicles because it costs money to put them there. It's far cheaper to set maximum factory performance parameters well within the safe limitations of the equipment. Easily done with modern electronically controlled engines.

Then, when those same customers bomb their trucks with in-line fooler boxes and ignorantly ignore EGT, carnage follows. With just a mild tuner box on my common-rail, I can go past 1300 pre-turbo degrees in a handful of seconds - on flat ground.
 
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