My 1980 240 DL overheats badly. Even in cool weather the needle begins touching the read area when I drive over 55 mph. I have done a lot of testing and some part swapping, but no success. Below are the tests I have done.
Tests done:
- WATER PUMP tested O.K.: to test, I took thermostat cover off, took the thermostat out, and cranked the engine, which produce a good squirting.
- FLOW INSIDE THE ENGINE block O.K.: the above test should have prooven that there is no obstruction in the water channels of the engine block.
- RADIATOR flushed and cleaned and tested O.K. (pressuring water into any of the connectors will produce a good squirting of water out of all other connectors; also, after driving, the radiator is evenly hot, though cooler at the bottom, which should be normal)
- HOSES o.k.; top hose off of thermostat is quite hot, lower hose feeding water pump is somewhat cooler
- FAN o.k.; creates good strong back flow
- THERMOSTAT is new (also did an independent "thermostat test" in which I removed the thermostat altogether, so that the flow (where the thermostat normally sits) is wide open -- this had NO effect; still overheating)
- RADIATOR CAP is tight; system is holding pressure O.K.
- Exhaust is dry and clean, no smoke or steam.
Can anyone suggest any other conceivable cause of the overheating, and how to test for it? Thanks for your help and advice.
WOlfgang Santa Barbara