300SDL Overheating
 

Long story short--my heater wasn't working--it would work if the car was warm already and sitting still, but once I got to highway speed, it would start to blow cold air. I took it to a local guy--good guy, but not MB experienced--and he replaced the thermostat. Now I have heat (though it's still a bit touchy), but the first day I drove it to work, the engine temp rose quickly above 90C, and would have kept climbing if I hadn't gotten off the highway.

However, even at "driveway" speeds, it will overheat. This has NEVER been a problem before--it seems too much of a coincidence not to be related to the t-stat, but I don't know.

There are good MB mechanics in the area, but they're all 30-40 minutes away, and I'm afraid to take the chance.

Could this be just a burping problem with the a-freeze?

yes, i was going to suggest checking your coolant level.

after draining you have to get it hot enough to open the stat to get flow so that the air can be gotten out.

tom w

There are a couple of temp sensors at the upper hose fitting on the head. You can use one of them to bleed the cooling system.

Intermittent heat with the car at speed indicates a bad monovalve. Do a search on monovalve cartridge.

Sixto
93 300SD 3.0

Could be an air bubble in the system. I don't know how familer you are with the 603 but whatever you do DO NOT OVERHEAT THAT ENGINE!!! It will be a $3k mistake.

If you can't figure it out have it flat beded to a shop.

All the symptoms of a reversed t'stat. My $.02.

Okay, reversed t-stat, air in the system, and possibly a monovalve at the start of my problem. :1blank:
Reversed? I've read that there's an arrow--does this point to the sky or the ground?
Any other suggestions?

Make sure you get all the air out of the system.

Reversed in the sense that the flat disc on the 'stat is facing the radiator instead of toward the rear of the vehicle. If it's installed properly, the small flat disc faces rearward.

If there is an arrow, it should point upward, but, my brand new Wahler has no arrow.

Doesn't the 603 water pump housing have a notch to clock the thermostat?

Sixto
93 300SD 3.0

Yes, I think it can only go the one way.

Yes, it's notched to be clocked in only one way. The side with the spring goes into the engine. All that is needed to replace it is a 13 mm wrench. I found it more efficient to take the top rad hose off and pour antifreeze in there till it was full, put the hose back on. then fill your tank and rad
make sure your heater is on when you start the car. I had the same heater problem. 99.9% sure that it's the monovalve. Probably a torn diafram. (sp??) A monovalve is only 4 screws to take off. No big deal.

Could be a bad t-stat, even if it is new. What brand is the new one?