coolant system pressure - Page 3 - PeachParts Mercedes-Benz Forum

its_snowing · #31 12-20-2006, 07:27 PM

well, during my recent misadventure with the monovalve, i drained almost 100% of the coolant out, and then refilled it. but the problem is the same after as it was before. also, when the heat is not on, as one would suspect, it runs significantly warmer (90-90 rather than 80-85).

rrgrassi · #32 12-20-2006, 08:51 PM

Quote:

Originally Posted by tangofox007

When you say "stuck closed," which valve are you referring to?

Talking about the thermostat. Only a failsafe is engineered to stick open in case of failure. Normal ones are not. They usually stick closed. Only the lucky people get them to stick open.

tangofox007 · #33 12-20-2006, 11:31 PM

Quote:

Originally Posted by rrgrassi

Talking about the thermostat. Only a failsafe is engineered to stick open in case of failure. Normal ones are not. They usually stick closed. Only the lucky people get them to stick open.

A bypass thermostat has two valves, the main valve and the bypass valve. So you can have varying combinations of "stuck," with varying results. But, because of the design, both valves sticking closed and causing the "no flow" condition that you referred to earlier is nearly impossible.

Brian Carlton · #34 12-20-2006, 11:37 PM

Quote:

Originally Posted by tangofox007

A bypass thermostat has two valves, the main valve and the bypass valve. So you can have varying combinations of "stuck," with varying results. But, because of the design, both valves sticking closed and causing the "no flow" condition that you referred to earlier is nearly impossible.

The two "valves" are on a common shaft. When the main valve opens, the bypass valve closes as the common shaft moves rearward.

I'm sure that it's possible for the thermostat to fail to "open" resulting in 100% bypass flow.

It's not possible to have 0% main flow and 0% bypass flow.

hey_allen · #35 12-21-2006, 12:41 AM

Regarding where to burp the system, you can often get most of the air affecting the thermostat out by loosening the clamp on the thermostat housing and slipping a thin screwdriver under the hose to let any air trapped in that high spot.

Another option that I seem to remember being brought up fairly recently, is to just park facing up hill, possibly with the right front corner highest if possible. This should allow the bubble to move forward to the radiator, and then up into the reservoir.

Just having an air bubble around the thermostat can cause the overheating as well, due to the air not transferring the heat to it anywhere near as well as the coolant will. I found this out after having gone around and around with an Isuzu engine that put the thermostat on the very top of the engine, above the coolant fill port on the radiator.