My 1997 E320 is within spec temperature when idle or just cursing. It overheats into the red zone when driving uphill. I read a lot of the previously posted threads and did the tests. Most of the radiator surface is cold even when the coolant is boiling. The lower hose is hot as well and it rules out a faulty thermostat. It looks like I need to change the radiator. I am thinking of changing the fan clutch, expansion unit can and all the hoses while I am doing the job. Is this a good idea? This car has over 100K.

I just flushed the radiator a few weeks ago and replace with 50/50 MB coolant mix.

The question I have is that how much transmission oil do I loose in the oil cooling area of the radiator and how do I add the lost oil back into the transmission. I just had the dealer do transmission oil and filter service recently, so I think I just need to add the lost oil. Correct?

It has been several years since I have changed a radiator and this will be my first MB radiator swap. Any advice is greatly appreciated.

I love this forum. It is very helpful and very educational for me. Thanks everyone.

 

Why does a hot lower hose exclude the thermostat? Have you removed it and tested it in a saucepan of water? Does it open OK at about 90degC
Why do you think the radiator is blocked? If you drain with the radiator still in situ (no need to drain gearbox cooler) does water from a garden hose etc pass thru the radiator OK?
The radiator could be blocked but how about a bad water pump?
Are you sure the system was correctly filled with antifreeze after the flush. It is quite possible to have an air lock.

Stuart

 

I drove the car after the flush for a few weeks without any problems.

To compensate for the transmission oil would be in the case of replacing the radiator.

 

If it worked OK for several weeks why would the radiator SUDDENLY get blocked.
The water pump and or thermostat could fail SUDDENLY however.
Stuart

 

There is a Valeo radiator is on the car. I am not sure how the inside of the radiator is constructed. Only the right compartment of the radiator where the water hosed are attached were running hot and the rest of the radiator was cold even when the coolant was boiling.

It seems the water is not circulating through the entire radiator and it only travels from the upper hose through the right compartment and through the lower hose.

Auxiliary fans were working fine. It was difficult to do an accurate test of the fan clutch because the radiator area around the fan clutch remained cold and there was hardly any heat transfer between the radiator and the fan clutch.

I doubt if there is a faulty thermostat, because temp reading is normal during idle and cruising for a long time. It only goes to the red zone driving uphill. I am going to test the thermostat tomorrow just to be sure.

 

What is a good way to test the water pump in this case?

 

Thank you very much snanceki for your advice. It was a faulty thermostat. Replacing it fixed the overheating problem.