Permanent Open Thermostat Question - PeachParts Mercedes-Benz Forum

sarah wilds · #1 09-08-2009, 10:47 PM

My car kept overheating. My mechanic replaced the thermostat, then the radiator, then the water pump. Still overheated. He realized that the thermostat does not open properly when installed in the vehicle (does fine in boiling water). So he rigged it open permanently with a screw. Is it okay to have it like that forever? Any other suggestions? It seems like the encasing is the problem as it only gets hot on one side of the thermostat encasing. Hope this makes sense! I live in north of San Francisco so it never get VERY cold, but still, inquiring minds want to know.
Thanks!
Sarah Wilds

#2 09-09-2009, 01:40 AM

Why did he not just go ahead and replace the thermostat? They are cheap.

Running with the thermostat is a VERY bad idea in ANY climate. It's probably worse in a cooler climate.

There are two reasons for this:

First, the coolant will never reach a temperature that will make the heater very effective if you need it.

More importantly, your oil temperature will not reach the level that it needs to be in order to boil off the moisture in the oil. This will cause the engine to sludge unless you are changing the oil every few hundred miles.

Additionally, if the only way for the engine to not overheat is to block the thermostat open, there is something wrong with the engine or cooling system.

Good luck,

280EZRider · #3 09-09-2009, 01:19 PM

Your mechanic was right in testing the replacement thermostat, but that's what he should have done with the original before buying you another one. Water temperature is what opens & closes the thermostat - which obviously requires water flow - so I would suggest thoroughly flushing the cooling system. It's possible that a blockage is not allowing sufficient water to flow through the thermostat housing.

kwontumspeed · #4 09-09-2009, 02:32 PM

Sarah, do yourself a favor and please find another mechanic...

tinypanzer · #5 09-09-2009, 05:20 PM

Quote:

Originally Posted by LarryBible

Why did he not just go ahead and replace the thermostat? They are cheap.

Running with the thermostat is a VERY bad idea in ANY climate. It's probably worse in a cooler climate.

There are two reasons for this:

First, the coolant will never reach a temperature that will make the heater very effective if you need it.

More importantly, your oil temperature will not reach the level that it needs to be in order to boil off the moisture in the oil. This will cause the engine to sludge unless you are changing the oil every few hundred miles.

Additionally, if the only way for the engine to not overheat is to block the thermostat open, there is something wrong with the engine or cooling system.

Good luck,

Exactly right, except Larry meant to say "Running without the thermostat is a bad idea".....

Your mechanic is a knucklehead for not addressing the true issue and you were very right to be suspicious. That's the kind of repair you do only when stranded and trying to make it home. Then you fix before driving again.

#6 09-09-2009, 05:37 PM

Good catch. I did mean to say running WITHOUT the thermostat is a bad idea.