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Old 08-17-2012, 12:23 AM
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Join Date: Feb 2011
Location: Elverson PA
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Help! Cooling system problems

Last summer drained the coolant out of the radiator and ever since the cooling system seems to be using fluid especially noticable when i go on long trips at high rpms. The engine temp according to the instrument cluster is at 90C generally and fluctuates between 85C and 100C depending on how hard I work the motor. This week, did a fresh coolant, water pump and thermostat change. I tried to get as much coolant out as possible. The results are the same. The systems seems to be slowly using coolant. I notice nothing in the oil to indicate a bad head gasket. I see a little white smoke at startup sometimes however it goes away as soon as the car has warmed up and I notice no lack in power or performance. about 17sec from 0-62mph and new the car calls for 15sec I believe. Is it possible there is an air pocket in the system somewhere?? All ideas are greatly appreciated. Auto in question is 1991 350SDL

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Old 08-17-2012, 06:21 AM
t walgamuth's Avatar
dieselarchitect
 
Join Date: Apr 2005
Location: Lafayette Indiana
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Steam on startup can be an indication of a leaky head gasket or cracked head. Small fault in the sealing of the coolant from the combustion chamber allows coolant to seep into combustion chamber. While engine is running it is a small amount and undetectable. When you shut off the engine the residual pressure in the cooling system pushes a little coolant into the combustion chamber and creates a puff of steam on startup. If not corrected could advance itself to hydrolock and a bent rod.

There is not a lot of space in the combustion chamber of a diesel for any liquid to accumulate.

The 350 SDL engines are notoriously known as rod benders. There is a never ending discussion as to the cause of it but one theory advanced is coolant or oil seeping into the combustion chamber on shut down.

Personally, I'd be looking for a good used 3 liter (earlier) 603 motor for an exchange if the car is worth major work to save.

(I had a 91 350SDL....lovely car to drive with a sumptious leather interior.)
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Old 08-17-2012, 10:54 AM
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Location: Elverson PA
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Shouldnt I notice an obvious lack in power? The previous owner before me told me he replaced the head gasket before I bought it. The smoke I had attributed to the egr removal and straight pipe exhaust system I added. My old 300D used to do the same thing at warm up sometimes. If the head gasket is slowly going bad wouldnt the exhaust be white all the time? Not to mention a definite odour of antifreeze?
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Old 08-17-2012, 05:40 PM
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Quote:
Originally Posted by jhertzler1103 View Post
I notice nothing in the oil to indicate a bad head gasket.
Now, you didn't just visually take a look at the oil and attempt to get to that conclusion...............?

Spend the $20. and send a sample for an oil analysis. You're looking for glycol and high sodium levels. Be sure to do it after you've run several thousand miles on the oil to get an honest reading off it.
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Old 08-17-2012, 06:00 PM
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smoke gets in your eyes
 
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Location: Eastern TN
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For the relatively low cost, get a new reservoir pressure cap. Make sure it's rated for 1.4 bar and/or marked 140 if that's what the car calls for.

If that doesn't do it, rent a cooling system pressure tester and have at it.

Sixto
87 300D
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Old 08-17-2012, 10:04 PM
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Not familiar with the later engines and designs but the OM617 can easily get an air bubble in it. Searching on 'burping' for solutions.

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