intermittant overheating

[Rauchen]

Hi Im new to the forum. I found this forum while searching about heater blower controls on my Mercedes.
Anyway I have a 1971 280SEL with the M130 6cyl. I have flushed the cooling system and replaced the thermostat, but it still overheats momentarily about 50% of the time. This happens during warm-up and seems like the thermostat is sticking. It will rise to 225+ then release and the temp will come back down to normal. Other times it seems to open just like it should. I've even taken the thermostat out a couple of times, checked for dirt, then put it in water with a thermometer, and heated it up to make sure it opened properly. It did. My only other recourse is to assume that the thermostat is faulty and buy yet another one. Any ideas?

[Arthur Dalton]

Most likely suspect is trapped air..
Park car on an incline, front up, ..heater on full , cap OFF , and run the car while watching the coolant level..it will burb itself..it also helps to sqeeze the rad hose slowly a few times after therm opens ...wear gloves.
If you are assured it is then not air-locked, I would change the thermo..the pot test does not always work for a sticking thermo b/c it is not in it's in-situ mount condition.

[mbgingerbread]

Hello Rauchen;
I am sure someone will be along to help you with your cooling problem; however, I have a 71 280se with the M130 engine. Recently, I discovered that the two metal pipes which run from the block to heater core on the right side are corroded and have been leaking ever so slightly-I don't know if your 280sel is setup the same but if it is there might be a problem with those pipes.
Otherwise, Iwould check for any sources of trapped air and bleed as necessary.
Turner

[sjefke]

And if the preceding suggestions don't solve it (I also suspect trapped air), check whether the sensor is malfunctioning. It's a long shot, but then again, you never know.

Bert

[meltedpanda]

and sometimes the thermostat is posistional, in other words, look for a small arrow stamped on the T stat , that needs to point up

[230/8]

There usually is a small hole in the lip of the thermostat. This needs to be up at the top of the mount so air can bleed out. If you do not bleed the air you can get over heating..people call it burping the system but all it amounts to is purging the air.

230/8

[Rauchen]

So essentially it is a vapor lock situation. I will definitely try that, it makes sense. Thanks a bunch for the help guys.

[bwostosh]

There are two thermostats which fit, air bleed ball check valve on top, or air bleed check valve on bottom. get correct one. V8 or 6 makes a difference. (I forgot which, age related C.R.S. syndrome)

The small pipe between water pump and head is critical too.

[Rauchen]

Originally Posted by bwostosh

There are two thermostats which fit, air bleed ball check valve on top, or air bleed check valve on bottom. get correct one. V8 or 6 makes a difference. (I forgot which, age related C.R.S. syndrome)

The small pipe between water pump and head is critical too.

I am going to see if I can find out which is which. Because when I bought the thermostat at the local O'Reilly's, they said it wasn't number specific and it would work "no big deal" maybe I got the wrong one.
The small pipe between water pump and head is critical too.[/quote]
what do you mean critical? for a leak or clogged?