Thanks for the tremendous show of support. I just about had a coniption earlier this afternoon which has effectively put me square towards the DIY mode from hereonin...

I had the driver's seat control brain replaced on the 300 TE by a fellow who originally told me $160... and now has asked for an extra $100 for the repair on the guise that it took him over three hours to remove the driver's seat and replace the seat control brain. After dealing with two shops that couldn't solve a simple problem in over two weeks to save themselves from first base (a 96' diesel I had needed a fuel filter to improve start up), I'm ready to do what I can to avoid further extortions.

"The fans you see turning are running in tandem at slow speed. They don't go on high speed until about 110 degrees. However, both should be turning at the same speed, either on high speed or low speed."

They aren't going in tandem. The one on the front of the radiator is spinning fast while the one in the rear is spinning about a third as fast. I'm going to use the towel test when I get back home to see if I need to replace the fan clutch.

"I think that the oil pressure gauge may be off. My 300TE runs at full oil pressure when the engine is under load (accelarating or going up a hill). I think that yours is running too low. This is especially so in light of the fact that it seems to run normally at first, but then drops."

I wouldn't be surprised. I have a friend of mine who would be willing to test it for free. I've done a lot of good favors for him over the years and wouldn't mind getting the needed expertise for this problem.

Related to this... I'm almost positive they used 10W30 and a cheap Wix filter. I'm going to replace the oil with 20W40 and a Mobil1.

"Other than that, you might want to check that the cooling system does not have an air pocket in the cylinder head. this will cause the symptoms you describe. the bleed hole is a fiddly bolt in the cylinder head, between the sensors towards the front of the engine."

I need to figure out how to diagnose this.

"Oil pressure is wrong. I would swap out the sensor first from one of your other W124's if you still have them."

Ditto on this. I've worked on everything from Vespas to Peugeots in the past. Time hasn't been on my side as of late but that should change this weekend.