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  #1  
Old 06-07-2010, 09:42 PM
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Location: northern VT
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This should not be that difficult! RE: thermostat

I replaced a thermostat that was running cold. (about 60*).. on my 300TDT. So it now runs hot..

yet the upper radiator hose also gets hot suggesting that the thermostat is at least a little bit open, and the top tube of the radiator also gets warm, but there must not be enough flow to actually cool off the engine.

So I began to think the radiator was plugged, and swapped that out.. still the same problem..

so does this have to be an air bound thermostat? I remember having this trouble a couple of years ago, and managed to solve the problem by pouring additional coolant into the block through the upper radiator hose. that has not helped this time.

any and all experienc and suggestions welcome.

Jason

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  #2  
Old 06-08-2010, 11:33 AM
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this problem keeps appearing on a regular basis around here.

I have struggled with it too, this is what I am currently finding.

-If your temperature is not spiking drastically or dangerously, you have removed enough air for the system to circulate.

-it is very important, for those of us with older vehicles, to verify the accuracy of the gauge before jumping to to such wild conclusions... it could just be a grounding issue. ( see charmalu 's thread)



-Here is where I start talking ridiculously - my new Behr thermostat continually ran just a hair under 100*c even on cold rainy days. I have a new Nissens radiator, aftermarket water pump , refilled visco clutch, 140 radiator cap (newish) and an 'adjusted' bi-metallic strip.

I decided to wait it out, this week has been hotter and the driving more demanding... the gauge is now showing 90*c max except on long steep hills. But I am still not reaching the previous highs.

This trend of lower operating temps has been continual, albeit slow, for the last couple of months... I only drive 150 miles a week.

What I am suggesting is that the new thermostats have a break-in period. Slowly, they will settle to the desired range. If you are not overheating, perhaps you should just chill out.
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Old 06-08-2010, 12:00 PM
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Location: Annapolis, MD
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Really frustrating, but I've had the same thing happen with 2 new Behr's in the last year.

Cooling system was otherwise unchanged except for the t-stat...new Behr sent it up to 100 degrees C...after about 1000 miles, it's at 90 degrees C.

There are several threads on this recently.

Confirmed with an IR thermometer.

I'm not too happy with Behr, Stant sells one cheaper at Advance Auto, and I think theirs has a warranty for life...and it actually runs at the stated temp when you put it in the car!
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Old 06-08-2010, 12:33 PM
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Thanks for your response..

I am guessing then that it is a thermostat issue..

but the radiator does not even get hot enough to get the fan clutch to engage.. maybe there is an air bubble behind the water pump? Ohhh. hey isn't there a little vent tube between the head and the water pump..

Two years ago when I did a citric acid flush, I elected not to touch it, as I figured was best left alone. I still don't want to touch it!!

at present the car is parked facing up hill, where I shut it off last night after the test run.. will go out and see if the upper radiator hose is empty of fluid.. and cross my fingers.

Thanks again for your supportive responses.
Jason
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Old 06-09-2010, 07:55 AM
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Depends how hot is "hot" I guess!

There are a lot of threads here on filling the system, the 300D's (with overflow) are more complicated than my 240Ds. Upper radiator hose method (fill with coolant and reattach) seems to be the preferred way.
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  #6  
Old 06-09-2010, 12:47 PM
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As to "burping" the system..... I've done quite a few 616 burpings after radiator flushes and for some reason the "burping" on the new 300TD went much easier. Heres how I do it..... jack up the front end, turn the heater on full, disconnect the heater hose at the driver side fire wall, leaving the hose on the engine, wire the hose end up. disconnect the upper radiator hose, leaving it on the radiator and holding it up, stick a funnel in the end and fill her up until coolant comes out the wired up heater hose, Put the hoses back on, start the car and wait until the heater starts putting out heat which indicates all is well.

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