update to temp problem - PeachParts Mercedes-Benz Forum

its_snowing · #1 12-22-2006, 07:11 PM

my car: 1982 300sd.

so, as mentioned in other threads, ive been having a little bit of an issue with my running temp. problems mostly occur when driving around town, at which time idling temps can reach up to 100 degrees. regular driving, and especially on highways yields temps from around 80-85 degrees. at the same time, i have had occasionally mediocre heat, which may or may not be related/imaginary.

with the engine cold, i can squeeze the upper radiator hose fairly easily, and there are no bubbles in the reservoir running with the cap off. i have no coolant in my oil, no oil in my coolant. engine has notable blow-by, judging from the amount of smoke visible in the valve cover with the cap off, and consumes maybe a quart of oil every 1500 miles. there is occasional white/gray smoke when leaning on the accelerator. my heat has also been marginal, at times, and today, after a fair bit of city driving, i noticed that the front of my radiator was cool the the touch, though the rear (engine side) was nice and warm, though not hot enough to prevent me from laying a hand on it.

anyhow, i dont think its the fan clutch, because the problem occasionally occurs just from warming the car up, and i can see the fan spinning well at idle. radiator cap is brand new. i was thinking it could be air pockets, but the coolant has been completely drained and refilled since, to no avail. also maybe a bad water pump? its not leaking. also, in the morning, after sitting all night, the cap opens with a crisp pop, though no coolant bubbles over.

should i be worrying about anything worse than a water pump/air pocket/clogged radiator at this point?

rrgrassi · #2 12-22-2006, 07:25 PM

Cold radiator, and warm engine usually indicates a stuck closed thermostat. Was the t-stat changed or tested?

t walgamuth · #3 12-22-2006, 08:23 PM

well, yes, also could be no stat in there.

tom w

its_snowing · #4 12-23-2006, 02:07 PM

unfortunately, the fact that i have on-street parking (and thus no work space), thats its been raining all day today, and that my girlfriend uses the car all day has prevented me from pulling out the thermostat and checking it.

but, i was able to take it out for a quick run this afternoon. after the car had been on the road, i pulled over. top radiator hose was hot, and the small section of radiator to the right (dirvers side) of that was warm. the rest of the radiator, and also the lower radiator hose, was completely cold. running temps on the car showed around 85 degrees.

PO had said the thermostat was newer, but im assuming that its stuck. no?

tangofox007 · #5 12-23-2006, 05:58 PM

It sounds more like an obstructed radiator. If the thermostat was not opening, the temp probably would not vary much as a function of vehicle speed. And the heater should work great.

its_snowing · #6 12-23-2006, 06:55 PM

yikes. what would account for the hose under the thermo being totally cold? i assumed the coolant ran from the bottom up. i dont want to buy a new radiator.

tangofox007 · #7 12-23-2006, 07:46 PM

Quote:

Originally Posted by its_snowing

yikes. what would account for the hose under the thermo being totally cold? i assumed the coolant ran from the bottom up.

A cold bypass hose (if that is the hose that you reference) would suggest that the bypass valve in the thermostat is closing as it should. (Which does not necessarily mean that the main valve is opening.) The coolant flow through the bypass hose (and the radiator) is from top to bottom.

If the lower radiator hose remains cold, either the main valve in the thermostat is not opening or the radiator is too obstructed to allow the coolant through. Or both.

its_snowing · #8 12-23-2006, 07:53 PM

yeah, the temp really doesnt vary with speed. in fact, it usually runs a little warmer when im driving slow, and cooler on the highways. but theres not much variance, usually.

t walgamuth · #9 12-24-2006, 01:11 PM

checking the stat is the starting place imho. it is pretty easy to do.

the toughest thing is draining the rad.

also be careful with the three 10mm bolts holding the stat housing top on. they thread into aluminum and like to sieze onto it. be liberal with pb blaster or such and start by wiggling them back and forth until you feel the threads are coming free. dont be surprised if you need new bolts. they also will corrode away. and when you reassemble be sure to treat them with anti sieze if you have some.

good luck

tom w