M103 Running HOT - Thermostat Question - PeachParts Mercedes-Benz Forum

taaboo · #1 05-06-2003, 08:00 AM

Friends - 89 300TE, started running pretty hot the past week or so, between 110-115, really bad yesterday. Pop the hood when I get home yesterday, here's what I find:

The upper and lower radiator hoses are both hot and not collapsed.
The entire radiator feels cool to the touch - the sides are a little warmer, but the back is just not hot at all.
Cooling fans work as they should.

SO - can a failed thermostat keep the radiator closed off like this OR am I paying the price for replacing the original Behr with a re-cored radiator a couple of years back when the neck broke off the original?

THANKS for your input!

Brian
89 300TE
01 Eurovan

PaulG · #2 05-06-2003, 08:40 AM

taaboo,

Yes a thermostst which has failed shut will give these synptoms.

Nice cheap fix......

#3 05-06-2003, 10:43 AM

The thermostat COULD cause this situation, but it's not likely. These thermostats are designed to fail open.

Good luck,

#4 05-06-2003, 11:34 AM

Larry,

Just curious as to how these thermostats are designed to fail open? I've heard of them sticking open or sticking closed, but never fail open as a design intention. Could you educate me please?

Jim Anderson · #5 05-06-2003, 11:43 AM

I've had them fail both ways, and an extra one...it came apart. I'm glad I didn't get pieces going through the water pump

#6 05-06-2003, 11:52 AM

I heard this somewhere, probably here. It was very believable for me because I have had several of them fail open, but I have never had one to fail closed. With American cars, my experience has been the opposite.

Sorry if I messed someon up.

Have a great day,

JDUB · #7 05-08-2003, 12:35 AM

My thermostat failed and seized a just open a crack . I boiled it in a pan of water to see what temp it would open and if it stayed open. The thermostat did not move but didn't close all the way. I was puzzled at first, I thought my radiator was partially blocked. The car ran at normal operating tempatures on the highway but crept upto alarming rates in traffic. Try a new thermostat they're not that expensive and it only takes a couple of minutes to install.

Alan Robertson · #8 05-08-2003, 01:54 AM

Larry has it about right. Older bellows type thermostats almost invariably failed closed. Modern wax thermostats on the other hand almost invariably fail fully or partly open.Failing open is obviously a much more desirable situation.

kennysin · #9 05-08-2003, 07:53 AM

I used to have a 1996 Volvo 850SE where the thermostat failed in the closed position. exactly the same problem: hot temperature, cold radiator.

Amazingly, convection cooling through the engine block was sufficient to prevent any catastrophic problems until it was fixed (it ran for a week in an English spring before the temperature rose consistantly to be noticed).

taaboo · #10 05-08-2003, 10:13 AM

Replaced thermostat, fixed the problem, car runs 80-90degC. Boiled the old thermostat for fun (worth doing just for the look from the wife), it did not open at all. Weird, cause it "looked fine".

THANKS for all the responses. First time I've ever had a thermostat fail, almost worth putting one by the tool kit in the back, such a simple repair.

Brian