300E Radiator, Water Pump, Thermostat or ??
 

Hi all,

I'm new to this board and I've been researching an overheating issue I have with my 92 300E. I haven't been able to find these exact symptoms in the archives so maybe someone can point me in the right direction to solve this problem.

Here are some particulars:
1. I observed a coolant leak on the radiator at the lower connection point below the water pump.
2. I tightened the clamp holding this tube and the leak has stopped.
3. I bled the system at the top of the heads and at the thermostat gooseneck. I also ran the engine with the coolant expansion tank cap removed to allow any air bubble to exit via the coolant expansion tank. I'm more than 90% sure I've successfully bled the system of air.
4. The on dash temperature guage will move up to 120C after a short period of driving.
5. The top hose going from the water pump into the radiator gets hot, (though not so hot that it burns your hand).
6. The bottom hose from the radiator to the water pump is warm near the water pump, but cold at the radiator side.
7. When the temperature guage is at 120C and the engine is turned off, the radiator is hot on the top 1/2 inch. The rest of the radiator is cool to the touch. (This may be caused by heat transmission from the hot coolant hose.)
8. The two electric fans turn on when the temp guage moves above 100C.
9. There is no evidence of oil sludge in the coolant.
10. The radiator and water pump were replaced 3 years ago by the dealer after the top plastic goose neck of the radiator broke. My wife continued to drive the car and ignored the overheating temp guage. This also caused a blown head gasket which was also repaired at the time.

So, if you have read through this long list, what do you think these symptoms point to? Is this a problem with the water pump, (which is where I think the problem lies), or the thermostat, or the radiator. Or perhaps even another component I haven't considered.

Thanks for your insights.

Drew Jenkins

Just a thought but you might want to remove the thermostat and run car and see what happens. Maybe you can then rule out the thermostat as problem.

Radiator
 

2001 E320 43k
Replace The Radiator Or Take It Radiator Shop For Cleaning, Its Plug Up Top To Bottom 2 Hrs Diy.

thanks Ron, that is a good idea that I'll try tomorrow.

Drew

i would definately
 

test the tstat while i am at it. too.

tom w

I have found that a leaky cap will cause my 300E's to overheat

Souns like a flow problem. If it's not the thermostat or coolant pump, I would say the radiator may be blocked.

Final diagnoses....
 

It was the thermostat. It has been replaced and all is well.

Drew

thanks
 

for the feedback.

glad it was an easy fix.

tom w

when you bleed the system you are supposed to run the defrost as this cirulates the water thru the heater system other wise you will still have air

Thanks hihosilver...
 

Coolant system was bled with heat on high defrost.

coolant leak
 

You might want to barrow an IR gun and see if the thermostate is opening at the correct tempature and see if what the rediator heat range is. If one side is hotter than the rest you may need ther radiator replaced. check gasket on radiator overflow tank to make sure it is in good condition and that the water and coolant are at level cold before starting.

Bob Geco

Have you tried a reverse flush of the cooling system? There are a lot of products to clean out cooling systems as this is a common problem.

Stick to what it says on the packet though, I thought that leaving the cleaning stuff in a bit longer would be a good idea, however I 'flushed' out the seal on my water pump.

If you think that there is a problem with the water pump, then take the thermostat cover of and half fill the system. You can then run the engine (from cold for a short time) and see if the pump is pumping.

It is is possible that the the impeller is damaged.