Recently purchased a 92 300TD with a 170k miles, and with the recent cold weather I thought it may have been normal for a diesel not to reach and maintain operating temp. Turns out someone had removed the thermostat. So now its head gasket time, or worse. Fingers crossed its not a head or cylinder crack. While I go through and replace the head gasket is there anything else I should replace for preventative measures? This is my first diesel and don’t have a clue.

Why do you think the head gasket might be bad?

We are not able to tie the missing thermostat to a bad headgasket based on the details in your message. Did you put in a thermostat and now the car overheats? People here have been known to buy a certain brand (or two) of thermostats that had a bad production run.

So give us a few more details of what's going on and we may be able to help more.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

Diesels actually lose heat at idle, since the air-fuel ratio is about 150-1.

Some diesels have electronics to detect this and bump engine speed up to maintain temperature.

http://www.internationaldelivers.com/assets/pdf/dyk168i.pdf

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

Ive heard the w124 has a reputation for head gasket problems. Bad head gasket = overHeating, so Im assuming the removal of the thermostat was a quick fix. This of course is speculation, but Ive got a feeling the head gasket is he case.

if it was leaking, you'd know.


It's either; consume coolant, have oil in your coolant/coolant in your oil AND you'd have some residual pressure buildup.


I have to do a headgasket on mine, as a coolant hose blew and I overheated it quite a bit. This car has 421k mile on it, and this is the second time the head will have been off (it was off at 380k due to a leaky headgasket)

The OM602 is a damn fine motor. Treat it right and it'll last longer than the car will.




Check timing (for chain stretch) I would replace the oil chain and gears (NEVER replace just the chain, same go's for the timing chain) check play on the turbo and get it rebuilt if needed. no would be a good time to check for wear on the lifters and valve stem seals. A complete head overhaul would be a good idea - you don't want to crack it open again. BE SURE WHOEVER YOU SEND IT TO HAS DONE AND IS KNOWN FOR DOING GERMAN ENGINE WORK. This isnt no chevy 350; even something as simple as using the wrong coolant during a valve regrind will end up costing you $$$....


VERY good cars, my 92 300d 2.5 was my first mercedes diesel, and it sure wont be the last.

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-1983 VW Rabbit LS Diesel (5speed, VNT/Giles build)

My experience has been when a car gets age and miles on it, cooling system becomes an issue. And if neglected can cause overheating leading to head gasket failure. In my case it turned out to be a hole developed between the
#2 prechamber and water jacket. Hence coolant being burnt, when at operating temp was like a steam engine out the exhaust. Read recent post, currently in the process of repairing. Mine was obvious what the problem was, somewhere in the head coolant was making it's way into the cylinder, no coolant in the oil. Have you put a thermostat in it? Quite a bit to check on the cooling side before you assume gasket is the issue.

im going to put in a thermostat today. Hope everything works out!

Hmmm, pulling the t-stat made my 87 300TD run a lot hotter when I put a load on the engine.....

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

Currently, the only time I can reach and maintain operating temp is on the highway, 90+ mph for and extended period. Otherwise, city driving the temp gauge only goes as far as 80C. Its ~25 in Chicago right now.

80C or slightly above is the normal operating temp. Sounds like you have nothing to worry about.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL