Hi again Peach friends. My newest 1985 300D seems to be running hot, Will go over 100C if i drive it like 5 miles. The radiator, however, remains cool. So far, i removed and boil tested the thermostat, and it is at or close to 80C. (P.O. sez he replaced it). So i drained the radiator, and it drained pretty readily thru the drain plug, so i don't think it is all that blocked. P.O. said they flushed it, but maybe not that thoroughly. Also drained the block. Refilled with clean distilled (rain) water and a bit of Shout detergent stuff. It took about 8 or 9 litres, and the reservoir was full, with much squeezing of the upper radiator hose.



With everything drained and refilled with clear water, i idled on my steep driveway (nose up) for about 30 minutes, and the guage settled at about 85C. It did not seem to "burp" even after idling on the steep driveway. But i took it on a short drive, about 2 miles including a steep hill leading back to the house, and the guage hit 95C. So i continued to idle it (nose up) on the steep driveway, and it remained at about 95C.



I took the following readings with my trustless brand new Harbour Fright I.R. temp gauge. Seems accurate tho, i tested on a real thermometer. These readings were taken with it idling nearly an hour including the short drive:



Ambient air temp about 15C
Head just below injectors 75 - 90 C (hotter near rear )
Upper radiator hose Thermostat end 80C, radiator end 60C
Radiator itself, about 20 C
Oil pan 75C
Reservoir 45C


Could it be the temp sensor (not sure where on the head that is)?


Could the propeller on the pump be bad? ***** of a job to pull that pump, hoping to eliminate other possibilities first.


Or could the radiator be that clogged, yet drain readily? Read elsewhere on the forum that the citric acid flush recommended could cause leaks.


Thanks for any suggestions!

The thermostat is opening but is it opening completely? Is it installed correctly?

http://dieselgiant.com/thermostatreplacementandmodif.htm

Sixto
98 E320s sedan and wagon
02 C320 wagon

Recently I noticed that my '81 300SD was running just a bit hot. Since I am the original owner, I know exactly how hot it should be.

Replaced the viscous clutch fan and solved the problem. Was an easy replacement.

If your fan continues to turn for a bit after you cut off the motor, it could be the viscous clutch fan.

Just my experience.

And I also replaced my water pump. Piece of cake. Just make sure you get a pump with cast propellers instead of the cut steel ones. By the way - the 37 year old water pump proved to be fine and I did not need to replace it ; my noise was actually from the AC compressor. So your water pump might be OK.

Compressor? How does a condenser make noise?

Sixto
98 E320s sedan and wagon
02 C320 wagon

First thing i checked was the thermostat; it was installed correctly, and it seemed to open pretty wide in the boiling water test. The radiator is remaining cool, even after running nearly an hour.



Wondering if the temperatures i posted are normal or too hot. Could it be that the sensor is erratic, and it never got hot enough to flow thru the radiator, and if so, why would the upper radiator hose be hot?


Where is that sensor located? I saw a few electrical connection on the Driverside of the engine just below the injectors. The temperatures there were around 80 C.



Is there a way to tell a bad water pump from a clogged radiator without pulling the pump?


Thanks!

Was the cooling system dirty? Run no more than 50% coolant to water.

If the radiator remains cool look closely at the external fins are they caked/blocked? Try shining a light through them.

If the external fins are clean AND coolant is flowing through the radiator then it is clogged internally. If coolant isn't flowing (one hose gets hot the other does not) then the thermostat or water pump is bad. It is rare that water pumps fail in a way other than leaking; but, pump fins can corrode

Good luck!!!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Is there pressure in the reservoir?

Sixto
98 E320s sedan and wagon
02 C320 wagon

Does anyone know if the temperatures i posted seem OK?



The fluid i drained was partly cloudy, kind of an orange tinged with brown. A few black particles. The inside of the thermostat housing had a thin , <1mm. layer of brown sludge.


Dumbly, i forgot to check the lower radiator hose. And now it is dark and raining. There was pressure in the res when running, but none when cold.

At 15C I would expect the coolant temp to stay at the thermostat opening temp. 95C isn't in the "danger zone" but definitely warmer than I'd expect and that comes from many miles of driving these. At idle it is usually difficult to get these up to temp, forget overheating/running warm at 15C ambient.

Sorry but I don't know for certain about the other temps you posted, they seem reasonable except for the radiator, i would expect that to be warmer. One way to test for a blocked radiator is to use an infrared thermometer like you are doing and look for cool spots. The cool spots are where the tubes are blocked.

Try turning the heater on high, if that drops the temp noticeably it would indicate insufficient heat loss vs. a bad thermostat causing too much heat...probably a blocked radiator.

Did the car sit for a long time? Pull off the upper hose to see if the radiator core tubes look crusty or blocked.

Look close at the external fins...seen them packed with sand/silt etc. causing overheating.

All that being said, short of finding a definite fault I'd try another new thermostat before doing major repairs.

Good Luck!!!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thanks, Sugar Bear, I never tried the cabin heat, but i did check the radiator in several spots and saw it was mostly one big cool spot, not much variation. From what you are saying, in our cool Autumn weather, maybe the radiator wouldn't kick in at idle, so maybe i will take it for a longer drive. I'm sure the 'stat is O.K. tho, P. O. sez he replaced it, and i boil tested it up and down a few times and it seemed to open and close nicely.



I will also pull that upper hose, and look inside, and also see if any heat is coming out the bottom hose.


I have this idea to direct a garden hose into the drain plug hole with the upper hose off, and if that doesn't work, i also have a 750 P.S.I. electric pressure washer. That might be overkill tho. Whaddaya think?



Not sure how long it sat. At least several weeks. I just bought it a month ago (for $250). It has about 230K on it. There is also some engine blow by, as the oil cap does a bit of a dance when loosened.

I do not know what is type of the cooling system on a 1985,but I have a W140 3.5,and the radiator is rarely hot when outside temp gets cold(below 5/10C),because it has a bypass passage that goes in front of T-stat,so when is colder outside and you are using your heating for cabin the T-stat rarely opens,because coolant does not reach opening temp that often,and the radiator remains cool.Don't know if that is the case with your car,just mentioning so you can check.

__________________
Mercedes W140, S350TD, 95.
Mercedes W140, S350, 92.
Porsche 944, 86 N/A.
Porsche 944, 85 N/A automatic.
Porsche 944, 84 N/A.
Porsche 944, 83 N/A.
Opel GT, 73.
Toyota Supra MA61,84.

A garden hose into the drain plug of the radiator or block is fine but only when the engine is cold, do not add cold water to a hot engine. No to the pressure washer.

If the radiator is clogged, flushing it will probably not clean it out. Not what you want to hear I know...

Does the radiator have any hot spots vs. cold spots? Check the external fins too.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

I pulled the upper radiator hose, and the clear water i put in is now the same shade of brownish orange the original fluid was. The upper opening is at a right angle and could see nothing of the innards of the radiator. Realized the temperatures i was measuring were of a cooler in front of the radiator, not the radiator itself. Too cold and windy today to do the reverse flush with the garden hose, but will warm it up and take it for another spin to try and get a better handle on the radiator temperatures, and hopefully tomorrow, with better weather, try the garden hose flush.

As you didn't run the heater even after seeing some brownish crud in the water jacket, there's not a chance it's properly cleaned yet .

Go back and do that, the citric acid thing really works wonders and doesn't cause leaks, it uncovers leaks that are there already and waiting to do you dirt .

Always run the heater on "max" when flushing, test the auxiliary water pump or simply unplug it and drive with the windows open of you get too hot inside .

80 ~ 95 degrees C is good but 100 is a bit too high, keep at it until you're sure everything is peachy .

Often when I remove the radiator I find the fins have accumulated crud in a circle where the air flow is greatest and you cannot see .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Another thing to check, is when the engine temp climbs, check to see if the oil cooler is hot. The oil cooler thermostat in the filter housing sometimes fails, and no oil gets circulated through the oil cooler. This will make your engine run hot.

Regards,

W.