I have been troubleshooting a slow coolant leak problem in my '96 E300D and think I might have it solved, with one unresolved issue, and wanted to run the situation and remedy by the experts on this forum for confirmation.
Problem:
For the past few months there has been a slow coolant leak. Filling the reservoir tank cures the problem for about 2 weeks. There are no visible signs of leakage (other than the reservoir being empty), the engine oil looks squeeky clean and the coolant also looks clean. Car does not exhaust any white smoke. Car does run a bit warmer than it used to - engine temps range from 85 - 95+ C.
Source?:
The reservoir cap looked like it might need replacing - visible signs of coolant on the underside of the cap, above the rubber seal - is this a sign that water was evaporating and engine not maintaining the required higher pressure? I could not find any signs of coolant exiting the overflow pipe.
Contributing factor:
I also just discovered this past weekend that the tiny v-belt powering the second auxiliary fan front-side of the radiator was off - probably thrown off by tiny rocks that I found beneath the aux fan unit.
Solution?:
I put the aux fan v-belt back on the pulleys and also installed a new coolant reservoir cap. After a few days of driving, it appears the vehicle is now holding the coolant, but the car still runs a bit on the warm side...85 - 95 C.
Is it possible that the preceding months of running low on fluid in effect lowered the water part of the mixture (due to evaporation through the reservoir cap?) such that I now have a greater than 50% concentration of coolant? I understand that high concentrations of coolant can cause your engine to run warmer. 85 - 95 C might be in the "normal" range for this engine but it does seem to consistently run 5 - 10 C warmer than it used to. I suppose I could go get a coolant tester and check the concentration - but I don't know how accurate they are.
Any counsel or confirmation from others that the above seems a rational explanation?
It is thermostat that controls your engine temperatures, unless for some reason the engine badly overheats and cooling system just can't catch up.
You did add water to the tank in last months?
Changing the coolant might be a good idea at this time.
Also getting infra red thermometer to confirm the temperature and track potential problems.
I added a 50/50 mixture of MB coolant and water each of the times I refilled the reservoir. I will continue to keep an eye on it for a couple of weeks to ensure that the new cap fixed the leak problem (assumed caused by evaporation from faulty cap) and will flush the system at the next service.
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