Hot 400E, not in a good way
 

Hi,

just got a 400E and drove it to Austin from Dallas (200 miles) and to work and back, waiting in traffic long enough to get it hot...let my wife take a test drive, and it comes back in 15 min with the temp guage in the red. She did not drive it hard. Opened the hood and found the cap blown off the coolant tank. We kept it running, aux fans and heater on, and a hose on the radiator, got it to cool down a bit. Turned it off, then back on, and it started out around 85C and went right back up towards the red. The coolant tank took about 3 quarts. So two possibilities, stuck thermostat, or an air bubble in the engine...are these good diagnosis, and how do I bleed the engine?
Thanks for any encouragement.

Is the main engine fan with the viscous clutch working properly? At high temps, this sucker should be fully locked up (not spinning freely after you turn off the HOT car).

I had a problem with high temps in my 1995 E420, and one culprit was a burned out low-speed aux. fan resistor. You'll find it behind the driver's side headlight assembly, down low. It's a rectangular metal piece with a coiled resistor inside. Mine was burned out and required replacement.

I'm not certain, but I think these engines aren't prone to bubbles in the cooling system.

Check the main fan and aux. fan operation and let us know.

Troy
1995 E420 95k

under control, more or less
 

I was able to run the car a bit, driving around the neighborhood, it started going high, to 100C then dropped back down to 85C. Each time I turn it off and let it cool down, it sucks the coolant out of the reservoir until it is dry, so will continue to baby it until full. The low coolant sensor does not. disappointing. It appears it just lost a whole bunch of fluid. Probably hurt the oil and trans fluid, a compression test is a good idea at this point, I believe. Thanks.

When my waterpump started to go out my car had many of the same symptoms; overheating, loss of water, etc. That might be worth taking a look at.

Quite common. Same issue came up with my 92 400E. Fan resister was one problem (fans were not turning on when the the AC was on) Radiator Cap was losing psi so I put on a new one.... that was is! Replaced Thermastat for good measure. Flushed system and everything is OK now.

Fan clutch hasn't been an issue for me but I have heard of that causing heating probs since they seem to wear out due to extreme temps under the hood.

Good luck