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  #1  
Old 11-07-2010, 11:29 PM
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Temp swing 300SD

Refribing a 1984 300SD. Replaced the radiator, thermostat and all rubber hoses, etc.. after a full coolant flush with the engine drain plug . Took four passes until clear water came out.

My question -at at idle up to 45-50MPH the temp guage sits steady at 85C. However on the highway at 65-70MPH the temp gauge is at 90C. (No AC or heat on in both cases)

Been two weeks and no change. I had though the faster speed would cool the engine faster

ANy thoughts?
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  #2  
Old 11-07-2010, 11:41 PM
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Where did you get the thermostat? I'd maybe pull it out and test it on the stove. See what temp it's opening at.

Also, maybe try a 'point and shoot' temp gauge to see if its really that hot.

HTH, Kat
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  #3  
Old 11-07-2010, 11:44 PM
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Quote:
Originally Posted by katubma1 View Post
Where did you get the thermostat? I'd maybe pull it out and test it on the stove. See what temp it's opening at.
The reported temperatures do not suggest a problem with the thermostat.
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  #4  
Old 11-07-2010, 11:51 PM
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Thermostat from fastlane here.

I have an IR gun & can get a reading when the MB is at idle in my drive way-but I cannot figure out how to get a reading from the IR gun when the 300SD is traveling 60-70MPH ;-)
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  #5  
Old 11-08-2010, 08:42 AM
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See if you can get this guy to get the temp from below...

http://www.imdb.com/media/rm1491638528/tt0082971
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mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)
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  #6  
Old 11-08-2010, 08:49 AM
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Quote:
Originally Posted by marybeth View Post
My question -at at idle up to 45-50MPH the temp guage sits steady at 85C. However on the highway at 65-70MPH the temp gauge is at 90C. (No AC or heat on in both cases)
The engine works quite hard at 70 mph and is running at 3000 rpm. It generates a fair amount of heat. The only way for the engine to increase coolant flow is for the thermostat to open a bit more.

The only way for the thermostat to open a bit more is for the engine temperature to rise a bit.

Many of these engines run all day at 90-95C. without any ill effects. Chasing this ghost is usually non-productive for most.

My '84 decided to run at about 96C. a few years ago without any obvious culprit. I did change the 'stat with no benefit. The radiator was also changed a couple of years later due to leaks. No change. I suspect the gauge but I'm not chasing it down.
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  #7  
Old 11-08-2010, 10:42 AM
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I hope you are correct. Not an issue now with the cool weather.

However I am in south Florida and have fears of waht will happen to the engine temps when it is 95F outside and the MB is stuck in traffic with AC on high
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  #8  
Old 11-08-2010, 10:50 AM
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Originally Posted by marybeth View Post
I hope you are correct. Not an issue now with the cool weather.

However I am in south Florida and have fears of waht will happen to the engine temps when it is 95F outside and the MB is stuck in traffic with AC on high
The fact that the engine runs at 90 on the gauge in cold weather is not firm evidence that it will overheat in hot weather.

The question is simply how much cooling capacity is being utilized when the gauge reads 90C? The thermostat may only be 1/2 way open under this condition, providing more than ample margin for those hot days.

However, be aware that few older vehicles can manage equilibrium at 95F. ambients without any airflow and with the a/c on.

The engine provides some overhead in this situation by allowing the temperature to climb toward the 120C. limit. It will likely do so until some airflow is established.

Last edited by Brian Carlton; 11-09-2010 at 01:33 AM.
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  #9  
Old 11-08-2010, 08:06 PM
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Originally Posted by Brian Carlton View Post

The engine provides some overhead in this situation by allowing the temperature to climb toward the 120C. limit. It will likely do so until some airflow is established.
120C. Wow. that's impressive.

Last edited by Brian Carlton; 11-09-2010 at 01:33 AM.
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