Thermostat Opening Temperature

[mbboy]

I was just wondering why the operating temperature of my 380sl goes above 100 degrees before my thermostat opens --- given that it's a new Wahler that's supposed to open at 85 degrees, and the previous thermostat -- which I think was a Behr -- did the same thing.

I also just noticed that Behr makes two thermostats for the 380sl; one that opens at 75 degrees and one that opens at 85 degrees C. So, I was wondering if the the one with lower opening temperature could somehow cause the car to run cooler.

Thanks in advance for the info.

[ScottinSoCal]

Originally Posted by mbboy

I was just wondering why the operating temperature of my 380sl goes above 100 degrees before my thermostat opens --- given that it's a new Wahler that's supposed to open at 85 degrees, and the previous thermostat -- which I think was a Behr -- did the same thing.

The thermostat is at the front of the engine, and the temperature sending unit for the dash gauge is at the rear of the engine, on the passenger side. I measured mine with a touchless infrared thermometer because it was running warmer in cool temperatures than it was on hot days and that struck me as odd. What I found was that on cool days the radiator and thermostat housing stayed around 165F while the engine area around the temperature sending unit was 185F. The only thing I can figure is the thermostat is partially open, restricting coolant flow and making the rear of the engine warmer. I would imagine most cars do it, but they don't install accurate temperature gauges. I know the gauge isn't accurate on either of my other cars - there's no way they maintain the exact same temperature at all speeds, uphill or down, no matter what the weather is.

[JPMOSE]

Some threads of interest:

http://mbca.cartama.net/showthread.php?t=9915&highlight=380sl+thermostat

380SL Temp Guage Reading?

http://www.benzworld.org/forums/r-c107-sl-slc-class/779564-84-380sl-overheating-maybe.html

http://sl107.com/eve/forums/a/tpc/f/2346035941/m/4171042462?r=3471055562#3471055562

[Lexxani]

I removed my faulty thermostat and left the system open. . .she'll always be at 175 in city traffic, and around 160-165 on the highway. . .

[Mike D]

That's not a good idea. You get away with it because you are in Florida. If you do that in colder climes you are asking for trouble. Mercedes uses all kinds of temperature sensors for various "warm-up" functions. If the coolant temperature doesn't get to about 180 degrees F (more or less) then you can have dis-functional timing advance and fuel enrichment problems.

[mbboy]

Originally Posted by ScottinSoCal

The thermostat is at the front of the engine, and the temperature sending unit for the dash gauge is at the rear of the engine, on the passenger side. I measured mine with a touchless infrared thermometer because it was running warmer in cool temperatures than it was on hot days and that struck me as odd. What I found was that on cool days the radiator and thermostat housing stayed around 165F while the engine area around the temperature sending unit was 185F. The only thing I can figure is the thermostat is partially open, restricting coolant flow and making the rear of the engine warmer. I would imagine most cars do it, but they don't install accurate temperature gauges. I know the gauge isn't accurate on either of my other cars - there's no way they maintain the exact same temperature at all speeds, uphill or down, no matter what the weather is.

Thanks for the info, Scott. However, I'm pretty sure that my temperature readings are correct for three reasons. First, my aux fan comes on app. when it should, and its sensor is also on the thermostat housing-- as you already know. So, the two reading seem to mesh.

Second, when i'm out cruising, my temp gauge typically reads anywhere between 80 and 90 depending on my speed and the ambient temp. (Boy, wouldn't it have been nice if MB had put a 90 degree mark on these gauges and/or calibrated them more exactly considering how anal we MB owners are about taking our temperatures :-) .

Third, according to the thread J.P. Mose just referenced (380SL Temp Guage Reading? , the 380sl thermostat normally opens above 100, and then settles down. According to the thread, higher temps can sometimes be corrected by drilling 3 small holes in the stat's frame and cutting its centering arm off, though i'm not really sure what that is. Are they talking about the arm that has to fit into the depression in the base of the thermostat housing before the stat can be seated? Sounds worth trying, but i still think that one or more of the usual suspects might be causing my temp problems.

I any case, one question that still remains is what, if any, difference would a 75 degree thermostat make in a car's operating temp?

Thanks for this and all the other very interesting thread going on here, guys.

[meltedpanda]

Dont know guys but my temp gauge stays rock steady at 175. It use to vary until I tore into the cooling system
recored radiator
repalced ALL hoses
flushed engine, including block and drain plugs
refilled with the "right color" radiator fluid
new Tstat.

Soooo , dont know if that what did it but it seems a good clean , next to new, sytem keeps the temp steady... I like to think my wrenching (and $) did it, but I might just be lucky