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  #1  
Old 01-20-2006, 07:39 PM
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Temp rising at highway speeds in '80 300SD

I just had a new t-stat and water pump put on my SD and now the temp goes up to about 100 (or is that line 90?- the one between 80 and 120) whenever I get up to highway speeds. Around town it's a little above 80 which is where I expect it to be. I checked the coolant levels and topped them off but there may still be an air bubble. But i don't see how that could affect it only at certain speeds. If it was a fan issue the temp rise would be reversed so I'm at a loss. Didn't find anything in a search either so hopefully someone here can help. Thanks.

John

'80 500SE AMG (yes, it's a real one)
'80 300SD

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  #2  
Old 01-20-2006, 07:51 PM
Geezer
 
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Location: Holland, MI
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Quote:
Originally Posted by white500se
...I checked the coolant levels and topped them off but there may still be an air bubble. But i don't see how that could affect it only at certain speeds...
There is a lot more heat load at highway speed than around town, so if there is a bubble, there might enough cooling to keep at 80C around town, but not on the highway.

Keep burping it...
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  #3  
Old 01-20-2006, 11:06 PM
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Quote:
Originally Posted by Jim H
There is a lot more heat load at highway speed than around town, so if there is a bubble, there might enough cooling to keep at 80C around town, but not on the highway.

Keep burping it...

Thanks, I'll do that.

John

'80 500SE AMG (yes, it's a real one)
'80 300SD
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  #4  
Old 01-21-2006, 09:55 AM
RAYMOND485
 
Join Date: May 2005
Location: CALIF
Posts: 508
Overheat

1984 300d Turbo 136k
Pull The Top Radiator Hose Off And Fill With Water Its Air In Top Of Engine,
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  #5  
Old 01-21-2006, 11:16 AM
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Location: Wesley Chapel, Florida
Posts: 231
Airflow

Don't forget to check the airflow through your radiator. I had a similar problem once. Too much road grit. Paul central FL

'84 300CD 290,000
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  #6  
Old 01-21-2006, 03:51 PM
Brandon314159
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And I've found that if your temp goes UP when the engine is idling (20 or more C) and then suddently drops as soon as you give it a tiny bit of pedal...that means its low on water.

I think what happens is that it gets just low enough to not allow the water to spill over the top rad hose properly.

Defintely keep on driving it...try parking it with the front slightly more inclined than the rear...that should help with the burping.
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  #7  
Old 01-21-2006, 06:01 PM
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Hmmm

If it is not an air pocket or trash blocking air flow, then it is a plugged radiator.
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  #8  
Old 01-21-2006, 06:02 PM
Hatterasguy's Avatar
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Yeah if you don't find an air bubble remove the radiator and clean the fins out real well. If that doesn't do it replace it.
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  #9  
Old 01-21-2006, 06:03 PM
Brandon314159
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Quote:
Originally Posted by whunter
If it is not an air pocket or trash blocking air flow, then it is a plugged radiator.
Plastic tanked merc. radiators do not often plug up...this is from the local radiator shop owners mouth.

Since he just did all this work on the cooling system most likely its still air causing problems.

I thought my rad was bad before too...talked to the guys at the shop...turns out my fan never full engages when it is supposed to. Another dead viscous clutched fan.

BTW I'd be lookin at the fan and other such things before I started dropping cash on the radiator...they are NOT cheap.
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  #10  
Old 01-21-2006, 08:06 PM
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Hmmm...

Quote:
Originally Posted by Brandon314159
Plastic tanked merc. radiators do not often plug up...this is from the local radiator shop owners mouth.
Below 150K, I might agree, above 150K and higher that statement is not correct.

Driver/style, miles per year, total miles on vehicle, chemical composition of the water used, climate, geography, frequency, and quality of maintenance, they all add up in long term durability.
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  #11  
Old 01-21-2006, 08:45 PM
240Joe's Avatar
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My vote is on a plugged up radiator. My 83 300D did the same exact thing, and it was caused by the orginal radiator being limed up so that the water flow through it was greatly reduced.

At highway speed, you don't even need the fan, and even if the air flow is a bit plugged up you still get plenty of air. But the water can't get through the radiator. You can have a radiator shop do a water flow test, or just buy another aftermarket radiator.

Joe
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  #12  
Old 01-21-2006, 09:12 PM
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Location: Holland, MI
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Quote:
Originally Posted by white500se
I just had a new t-stat and water pump put on my SD and now the temp goes up
I'm thinking this is a big clue...
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  #13  
Old 01-21-2006, 09:15 PM
Brandon314159
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Quote:
Originally Posted by Jim H
I'm thinking this is a big clue...
I agree....don't suspect the radiator just cause it "might" or "should" be bad I dunno bout you guys but cash doesn't grow on trees at my house

BTW 1981 300SD with 295k origional radiator.
1982 240D with origional (or so it looks) radiator and 312k

Both cool nice
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  #14  
Old 01-21-2006, 09:24 PM
240Joe's Avatar
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If he used mercedes quality parts for the water pump and the thermostat, and he filled the upper radiator hose with water/coolant to keep the air out, then I'd bet he's going to find it's the radiator has restricted water flow.

Wasting time fixing the wrong things is wasting money.

And just because you have cars with original radiators means absolutely nothing. All it takes is somewhere over the last 2x years, someone did a flush and filled it up with tap water with high mineral content.

Joe
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  #15  
Old 01-21-2006, 10:41 PM
t walgamuth's Avatar
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Location: Lafayette Indiana
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yeah

i would be double checking the t stat. and being sure there is no air in the system.

tom w

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