More Cooling System Problems/Questions
 

My 83 300D has been running what I think is warm, a bit under the 100C mark on the guage. Today I changed the thermo and put in new MB coolant and a new radiator cap. Still runs warmish, just under 100C. If I turn up the heat all the way the temp guage will drop quickly to maybe 3 needles width above 80C. No leaks anywhere and no wierd smells from the heater or under the hood.
Unscientificly feeling across the top of the radiator and it's hot everywhere. The drained coolant was very clean, no signs of scaling and in fact looked like it had probably been changed not too long ago.

Questions:
1. The fan clutch, Car is hot, I try to spin the fan and it'll go maybe a half a turn or so after I let go. Definitely some resistence there. Is this OK?
2. Water pump. No dripping or anything. Can it just plain wear out or would it leak if bad?
3. Pressure. There definitely pressure in the system, not a lot though. I was able to remove the rad cap hot with just a little hiss. Is this right or should there be a lot of pressure.
4. Am I being too anal, is below 100C ok for the old beast.
5. Could poorly set valves cause the car to run hot. I haven't yet set them and although the car runs good I do not know the status of the valve adjustment.
Thanks for any advice.

1. There should be some resistance in the fan. One way to test the fan is to observe it while turning off the engine. It should stop almost immediately.

2. Not sure about the water pump dripping.

3. There should be significant pressure in the cooling system if it's hot. I'd recommend doing a pressure test to see if the system holds pressure (this is done cold). This will also tell you if you have a blown head or head gasket.

4. You might be a little anal. ;) My car runs anywhere between 90 and 100C when fully warmed up and according to the correct temp rating of our thermostats (80C) this seems correct.

5. You definitely want to check the valve clearance. Seems to me like this is a commonly overlooked maintenance item, but it's probably unrelated to your cooling issues.

Mine always runs around 80*C, but I've been told my thermostat is bad. However I was also told that it should be in the 85-95*C range so 100*C is getting a little on the high side. If you cross 100*C it is time to do some investigating.

Might just as well adjust the valves it isn't hard at all, just takes little time.


Sigh I should change my coolant SOON as I have no clue when it was changed last, the radiator looks new but I have no idea when the coolant was last changed. Gotta get my new thermostat, I have everything else waiting....

rmmagow
 

Mine runs between 95-100*c all the time. I've gone round and round chasing small coolant leaks, swapping thermostats, changing an aux. pump and just yesterday a waterpump, etc. so I know the cooling system pretty well now. after swapping from a 87*c to a 80*c thermostat my gauge moved down not even a needle-width. Now with the new waterpump it runs a needle-width higher. My cooling system is flushed and clean. I can put my hand on the upper hose when just off the highway so I know its not too hot. I have come to the conclusion that the gauge is a little wonky. I use the gauge as a "trend indicator" rather than an absolute instrument. If your car runs at 100*c all the time, everything in the system is up to snuff and it doesn't boil over there is nothing wrong with the system, drive it and don't worry about it. RT

Voice of experience.....
 

Do I have to say it? NEVER remove your radiator cap to see if that 100-degree reading is accurate. I was lucky, but could have lost my face to the experiment. Wait til the damn thing cools.

About 100 is normal.. Some will try to make you feel its to hot...

The thermostat starts opening at about 92 to 95.. thats near 100... opens all the way at about 107.. about 110..

The fan clutch comes in at about 105 to 110.. You can check it by parking nose to a wall on a hot day with the windows down and running the engine at about 2500 or so RPM.. that way there is little air going thru.. in a garage helps as the heat stays near the engine.. At about 105 to 110 you should hear the roar of the fan as the clutch comes in.. You should hear the electic fan come on about 100 to 115 degrees.. you may want some one to hold the engine at speed and you stand up front where you can hear better... Open the hood and you loose the heat.. If you have a newer car with twin fans.. they should go on high about 115..

All in all.. 100 C is normal in warmer temps.. about 100 to 115 is where every thing should be doing its job..

If you are running under 90ish C in warm weather.. Replace the thermostat.. You are causing engine wear by running the engine to cool and using extra fuel..

Ken

The Mercedes 616/7 engine service manual states that the fan clutch engages when the coolant temperature is in the range of 90-95 degrees. The bimetal strip that activates the movement of the silicone fluid begins to operate at 73 degrees which I think is the air temperature surrounding the fan clutch.

You are right... 90 to 95 is where it starts to work.. But most do not really take hold so you can hear them until 100 to 110.. Thats when they are engaged full.. You have to remember that the engine temp is not what the water temp at the point in the raidatior that the fan clutch is located behind... so the water temp will need to be higher to get the temp in the center area of the radiator that the fan clutch is behind up high enough to work.. Thats why the bi-metal is at a lower temp.. 73..

One thing you always need to remember about the engine temp.. Its the temp of the engine.. Not the temp of the water in the radiator.. In most all cases its far cooler..




Ken

<One thing you always need to remember about the engine temp.. Its the temp of the engine.. Not the temp of the water in the radiator.. In most all cases its far cooler..>

Good point, because at 100 degrees, water boils!

I don't think this is true, that is if you have the 80C thermostat which is correct for these cars. From what I know the temp rating of a thermostat is the temp at which it starts to open. The Haynes manual also states that it should be fully open at about 94C.