Have been experimenting with my 300TE regarding it running what I consider abnormally hot. I know some are saying this is typical, but I don't buy it. I have NEVER owned another vehicle that ran in excess of 110C at any time unless it had a serious cooling system problem. The cooling system is either totally inadequate by design, or we are having some type of issue from an aftermarket part or other problem. When I was young and stupid, I had an old Datsun 240Z that the water pump locked up and wrung the fan off of. I put it back together without a fan and drove it that way in town for about a year. It was not much more different than this 300TE in terms of trying to keep it from overheating. That is NOT a good thing.

Here is what I discovered today. I believe the issue is with insufficient coolant circulation, as opposed to radiator efficiency or fan circulation. The radiator in the 300TE is nearly identical in size to the radiator in my Volvo 960 wagon, a 2.9L four valve, twin cam inline 6. The Volvo never runs more than 5 degrees above the thermostat temp, no matter the ambient temp, with or without AC running. That tells me the radiator should be adequate.

When I stopped today in a parking lot with it running at about 100C, I hopped out to do some other checks without turning the engine off. Just as I jumped out, the electric fans hit high speed, so I know the two speed fans are working. I used a rag and the fan clutch was delivering plenty of pull to the fan. I could not stop the fan. That says that the air circulation is as designed.

When I left the parking lot, it was raining pretty good. Temp was right at 100C by the time I got on the interstate a half mile or so later and ran in to a good heavy rain. I even got behind a semi to get a good spray on the radiator. The temp hardly changed, coming down to only 90-95C, at best. That cold water spray and drop to 75F in ambient temp should have dropped the coolant temp like a rock. Lack of it says to me the radiator and fan is not the issue. That obviously means that the cool water in the radiator is not getting properly circulated through the engine.

As I was getting off the interstate, I did one of my no fan tricks in the old Datsun and downshifted and coasted a half mile or so to the exit ramp. Temp dropped drastically. Closed throttle means no fuel being provided to the cylinders via the injection, so the engine is essentially air cooling internally. Same result going down a long hill a short time later. Again, saying the coolant has stagnated in the engine.

I really think there is a restriction of some kind in the system that is causing the water pump to fail to sufficiently circulate the coolant. Maybe the thermostat doesn't open enough and is restricting the flow. Maybe the water pump design is flawed and doesn't meet the needs in terms of flow and pressure to circulate the coolant.

I'm going to start with a different thermostat and see if it has any effect. Maybe the OEM thermostat has a larger opening than a typical aftermarket thermostat that meets the size and temp requirements? I am currently running a Stant thermostat I put in it about Feb, so it is new for all purposes. Does anybody know what the OEM Mercedes brand is? If not, I'll order a genuine Mercedes, but would rather not pay $50 for a $12 thermostat if I can avoid it.