Thermostat Question?????

[gvanhouten]

I just got another thermostat for my 87 300td. I took back the new one I bought from the dealership. I put the stat in water and slowly raised the temp and it opened just before boiling occured. The second one from same dealership did the same thing and same result. Thermostat should open in 80 degree water correct???? Need suggestions???????

[Habanero]

80 degrees Celsius=~176 degrees Farenheit

Both T-stats are fine.

[gvanhouten]

Well why was I a science major??? So I can forget everything I learned. Thanks for the refresher.

Did you measure the water temperature when they opened (cooking thermometer)? There's quite a difference between 176 F and 212 F.

[Hit Man X]

T-stats start to open at a lower temp than when they're fully open...

Originally Posted by Hit Man X

T-stats start to open at a lower temp than when they're fully open...

True, If I remember correctly the OEM 80 C stat is full open at about 95 C (203 F).

[t walgamuth]

a lower temp as altitude goes up.

so unless you are at sea level 212 is high.

tom w

[Pete Burton]

and while these thermostats move positionally primarily due to temperature, they are also affected by fluid stagnation pressure. (my, that's a clumsy sentence, isn't it? ) When they are installed and the engine is running they open up a little more and when the engine is running fast the water pump is pushing fluid harder against the thermostat and it opens a little bit more still. A superior yet more linguistically convoluted description of this phenomena can be found in the English translation of the factory shop manual. pfew!

[Habanero]

Originally Posted by Brian Carlton

212°F. is 100°C.

Any of these vehicles will run fine at 115°C. which is 239°F.

No boiling will occur because of two factors:

1) The coolant raises the boiling point to this level or above.

2) The pressure in the cooling system of approx. 15 psi (some greater) will raise the boiling point of water to approximately this level.

The combination of a pressurized cooling system and a proper coolant mixture will lift the boiling point well over 260°F. at sea level.

Yes, this number will drop with altitude.

Uhh, I think he was referring to the boiling water in the pan for testing the thermostat, not the engine itself.

[Ali Al-Chalabi]

There is usually a pretty good spread for where the thermostat starts to open until it is fully open. The temp stamped on the thermostat is when it starts to open. Don't know about the 80C thermostat, but the 87C thermostats are not fully open until they get another 15C warmer. Also, I have noticed that a brand new thermostat sometimes does not crack open the very first time right on temp. Every time I replace an 87C thermostat, I have noticed that it never cracks open the first time until almost 100C. After it opens and closes a couples of times, it starts functioning normally.