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?

Attached Thumbnails

 

Did you burp the air out when you refilled the engine?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

yes sir, that's the first thing I thought so I double checked it.

Yes, that's too high. My 81 SD always runs a little below the last white hash mark. Your is above the hash mark. Hint - it it gets so high that you are worried, turn the heater on high and it will cool down some; you can usually get home that way. Either heater or defroster - cannot quite remember but you get the idea.

yeah tried that trick but didn't make much change, yeah it used to run a just like yours now it has climbed, oil still looks good not like it's mixed with coolant, coolant looks perfect, not sure if HG is starting to fail or what's up

Maybe your thermostat is not opening quite right. I never figured out where the thermostat is when it needed replacing about ten years ago. Maybe someone can chime in and let us both know where it is and how much trouble it is to change it out.

well I should add, that if I am just driving around town even with the ac on, but keep it around say 35-45 she runs nice and cool, it's only when I get over 65 that it seems to climb.

Poor radiator flow or worn out fan clutch is my guess. You could try running without a thermostat for a day and see what happens.
Turning on the heat is a good idea to bring the temp down if your frickin CCU is working right. I've been caught in bumper to bumper traffic twice with my temp close to yours and the heat wouldn't work. I almost got out of the car at one point to disconnect the mono valve.

__________________
'81 300SD

That's not a real good plan on an engine with a bypass thermostat. Unless you are willing to go to the trouble of blocking the bypass.

If you're willing to remove the thermostat, put in a new one and be done with it.

Sixto
87 300D

Sixto - I agree but how about a few directions about how to find it and get it out. I looked briefly once years ago and could not really find it. Picture would be a great help.

This should help - http://www.peachparts.com/Wikka/OM617WaterPumpBypassHose

Sixto
87 300D

Don't forget that the thermostat can be installed backwards and it has to have the "arrow" up. But ya, the om617 can be temperamental temp wise. But once you get it figured out, it should sit at 80 all day and night. If that was a 603 I would be pooping my pants by now.

__________________
08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D

I'd be looking for an S350 in need of a short block

Sixto
87 300D

Considering that a properly operating thermostat only begins to open at 80 degrees and does not fully actuate until the coolant temp reaches 94 degrees, there is no basis for that claim.

Given the design of the thermostat housing, that would be quite a feat.