81 300sd, just replaced the water pump as it was failing all else seems normal. temps were seemed to be climbing and I could hear the pump beginning to fail, but after change of pump it still seems kind of high, this is driving for 10 minutes and getting up to 75mph for 5 minutes. outside temperature is 90 and ac was on, thoughts ideas?

 

Should the thermostat itself be drilled 3/16 hole to help the latter? Also, this ensures coolant is always flowing?

 

No I wouldn't touch the thermostat.
But what I would do is to get the front end of the car up on ramps to help the air in the system evacuate.
Just keep an eye on the temperature gauge while doing so and don't let it get any higher then shown in your picture.
Cheers
Big Dan

 

I went back and read my manual after a suggestion that I should drill the new T-stat ( I did not), and what u are saying is true. Why the hell do "experienced" BENZ-FORUM members suggest otherwise. Another thing is that this also warps the T-stat housing etc.

Your above pic has the T-stat with 2 O rings one in the Front and another in the rear?
I did not install the "simple O ring" on the rear of the T-stat as the manual did not illustrate that option for the 85 model housings.
However, every parts site has it with double O rings for the 85 models! Should I install it?

By the way its an OEM Behr T-Stat, and the T-stat did bring both o rings.

OOPS!

EDIT:
--------------------
I got my terms all confused. The Loped Rubber thing is a T-Stat GASKET not an O-ring. People call everything that is round and rubber an O RING.
Allow me then to rephrase my question.
Should later model housings(1985) have the O ring installed aside from the Loped Rubber Gasket on the backside of the T-stat?
The more I read the more puzzled I am. Some people say that the extra O ring in the T-Stat Behr package is for "block to housing seal"??

That sounds retarded. Cylinder head O ring? WEIRD!

No manual shows an O Ring installed on that side of the housing or at the cylinder head anyhow. Only gaskets. WTF?

From parts Geek. Quote: "Notes: 80 degree T-Stat Requires (1) 617 203 01 80 seal ring." Part 617 203 01 80 is basically that extra O Ring.

When I hit that part number up on several sites here is what come out=Thermostat O-Ring Seal -Thermostat Seal With Side-Hole
"This seal is used to seal the thermostat in the intake manifold". WTF.. Either Im way off or parts site call things what they are not?

Now Im lost....URG
8)

 

Try the replacing the cap on the radiator expansion tank

 

Check the wire coming from the temp sending unit on the left side under the fuel injection lines. I have noticed when it get a little frayed it will start showing higher temps.
Just pull that back plastic off and clean/strip the wire and solder it once again into the part that slides over the sending unit.
Seemed to take care of my 'overheating' problem.