I have a W124 1993 300D 2.5 turbo. I just replaced the water outlet ... thing because it had developed a hole and was leaking coolant everywhere. The repair was a success ... sort of. I refilled the coolant reservoir and took for a test drive. There is no more leak, but the temperature shoots up to 110 within just a couple of blocks. My coolant was green, now its water, but thanks to this forum, I plan to de-oil, flush with water, acid flush, remove block plug, water flush x5, and add the MB coolant. But before I do that I'm wondering if there is a way to test the water pump. It seems to me, unless the cooling system is full of sludge, which it doesn't seem to be since water flows through it clearly, it seems to me I should be able to go more than a couple blocks before over heating provided the water pump is working. When I drove it I ran the defrost to try to get water through the heater core. But even though the temp was off the charts, the defrost was still cold. Is it possible that the leak (and running dangerously low on coolant) caused damage to the water pump? How can I test it?
Sorry, I couldn't think of what it was when I first posted. It was the water outlet fitting for the heater feed that I replaced.
I've solved the overheating problem with the help from some members on another forum. The advise given to me:
Phil wrote: Here is a hint I have used on some cars. Disconnect the upper radiator hose from the radiator side and pour water or coolant in the end of the hose. On some cars the water doesn't get into the block until the water is hot and the thermostat opens so this method puts water on the other side of the thermostat so it gets into the block and head of the engine. I had to do it this way on my car.
Diesel Friend wrote: I second what Phil said. I would say that you have trapped air in the cooling system and therefore getting the high temperature. With the engine being cold I recommend you slacken off the hose clamps on the top rad hose. Remove the hose at the end pointing to the engine, twist it around a bit and fill the rad, then do the same with other end of the hose get coolant into the engine. Install the hose and tighten the clamps. Remove the cap from the coolant reservoir and start the engine and let it idle. Watch the temp gauge and also the resevoir.
At one point you will most likely see air burbing out. After this put the cap back one and take the car for a test drive. If everything is normal temp. should be about 80 Degr. F. All this with the thermostat in place. This procedure worked for me on 2.5 liter diesel non-turbo.
and Brian wrote: Exactly. The cylinder head cannot fill with coolant because the thermostat is closed. The coolant fills the radiator and the lower hose and comes to a dead stop at the thermostat. The only way to get coolant into the head is via the upper hose. You've got to remove the upper hose and fill the head with coolant which will eliminate the problem.
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