Temp too low? - PeachParts Mercedes-Benz Forum

CUBANDiesel · #1 11-13-2005, 08:29 PM

Greetings, just drove from LA to Bay Area in my 300SD. It ran very well, with no issues over the grapevine. While I thought it might get too hot, it actually ran very cold on the trip. When I drove down the grapevine, a 6% grade, my engine temp dropped to from 80c to 50c. Then it almost hit 40c. I was worried it might stall out. After the grapevine, the outside the temp was a steady 47-55 in the central valley, at one point it was 42 outside. The engine temp never went above 50c for 5 hours. Has this happened to anyone here? I appreciate not overheating, but can running this cold at 65-75 mph damage a 617?

By the way, using a high-pressure diesel pump was great just outside of Bakersfield. I put in 6.7 gallons in about two minutes. I wonder why those pumps are not more common?
Viva Cuba libre, - Cuban Diesel.

DieselJim · #2 11-13-2005, 08:35 PM

Running cold will never damage a diesel unless you have a malfunctioning sensor and you are really running hot! You may have a very low or stuck open thermostat. As a matter of fact the colder it runs the better it will run(within reason). This is only a problem if you need lots of heat(cold climate or veg oil heating needs).

Only bad think about high speed diesel pumps is the foam(I usually put in another half gallon or so after I let the foam settle). I love filling my diesel at my regular truck stop. I use the auto pump but it is still high speed.

Hatterasguy · #3 11-13-2005, 08:44 PM

I disagree running a diesel cold will kill it. Carbon will form and mileage will go down as a result of the fuel not buring completly. Diesel's are more efficient the hotter they get.

Replace the T stat and check the accuracy of your guage. 80c-100c is about the range one of these things should operate in.

whunter · #4 11-13-2005, 08:50 PM

Thermostat is stuck open.
Replace it and all should be well.

Ara T. · #5 11-13-2005, 08:53 PM

Warm diesel is a good thing, all the internal parts are designed for a specific temperature, and when they're cold the fitting of those parts wont be optimal. It sounds like your temp sensor is goin bad or plugged up or somethin, but it could be your thermostat as well. How long does it take for the car to warm up? Should only be like 1.5 miles/10-15 minutes or so.

t walgamuth · #6 11-13-2005, 08:55 PM

that is too cold. it should be run at the design temp. 80 degrees. i would never run one that temp. if it got that cold i would put cardboard in front of the rad to warm it up til i could fix it right.

in 1952 or 53 the briggs cunningham team had a chrysler 331 hemi powered race car running at lemans. the mechanic thought it might run too hot so he took out the stat. the car ran too cold and wiped the bearings long before the end of the race. nobody believed it was possible to run too cold at those speeds. (they were averaging prob 90+ back then).

also could be low on water. (back to your car).

tom w

#7 11-13-2005, 09:04 PM

My 300D was doing that when I first got it, turns out the stat was installed backwards. With the correct stat installed it stays at or above 80C, even in VERY cold temps.

Carleton Hughes · #8 11-13-2005, 09:07 PM

Same thing happened on my '84 diesel,thermostat was stuck open,also had this happen on a '93 Camry.

Cheap and easy fix.

DieselJim · #9 11-14-2005, 08:49 AM

I believe the right thing to do is to fix the thermostat. I also can buy the carbon build up. However there is no short term damage that would happen to the car and it is questionable what long term damage would happen especially if you are able to open it up and clean out the carbon going up that hill you went down. Any car would be more fuel efficient running cool(don't make me get out the thermodynamics book to prove it). BTW all you car lovers know your car gets better economy in cool weather all things being equal(take winter grade fuel out of the picture). The usual reason for running hot is to lessen pollutants. Running cool will enable the oil to more effectively cool the turbo and in general support more efficient combustion. I don't know all the tolerances but I doubt once you get up to a nominal operating temp(which this car was at) that any mechanical serious mechanical difficulties will appear.

t walgamuth · #10 11-14-2005, 10:43 PM

that the engine is prob not hurt.

i disagree that running colder than stock (i mean a lot, like at 40 degrees c) wont hurt the motor. they set them up to run from 80 to 120 degrees for a reason. cold oil on bearings i dont think is a good idea.

why are you supposed to take it easy til it warms up if it doesnt matter?

tom w