Hey!

Love the web site, love the advice y'all give.

I've got a question about some advice I got from the website regarding my 1985 300sd.

I looked at the thermostat replacement procedure for the w123.* I followed everything to a "t" with the exception of drilling the holes in the thermostat.

Backstory on my car;* The car has been in the family since it was purchased new. I know how to do most things but I'm in panic mode now.

With the harsh winter heading at us I thought it would be a good thing to replace my coolant and thermostat,* the procedure went off without a hitch. Until i started driving it. The car warmed up as it should but quickly started getting too warm. I also lost most of my heat.

(I noticed there is no bleed screw on these) I pulled the new thermostat out, replaced it with the old one, thinking I got a faulty unit. Still got too warm.

After that; I parked the car on a very steep incline brought it up to operating temperature,* squeezed the hose waited for the air to purge itself... no help.

I took it to a shop, they said that I might air trapped behind the heater core. The replaced all of the coolant and pressurized the system... no help.

I asked them if they thought it was a blown gasket. But I've had no power loss, no fuel, water, or anything weird in my oil, no excessive smoke. Nothing at all weird.
They checked the old thermostat and put another in... no help.

They thought then it might have been the water pump. I told them the car would cool down when I turned the heater on so I didn't think it was the water pump, we replaced it anyway... no help.

I'm at a total loss here fellas. My car is still getting uncomfortably warm and it really worries me. Can you throw a suggestion or two my way?

Any help appreciated
Thank you!

That thing about drilling bypass holes in the thermostat body isn't something you need to do on a routine thermostat replacement. It's something suggested by some people if the car has chronic overheating behaviour and everything else has been tried. Not everyone supports it as a good idea.

The OM617 is prone to air pockets when the coolant is refilled. People say that filling through the upper rad hose inlet to the block, preferably with the nose of the car elevated, is the best way to avoid an airlock.

I had exactly the same problem when I refilled the coolant after doing the water pump and thermostat last fall, and I had filled it through the rad hose. In my case I ran the car with the pressure cap removed, shut it down, then restarted. Also I am lucky that the PO, maybe because he had similar issues, installed a T fitting with cap on the upper heater hose and I also removed it, which I finally seemed to burp the system.

Air pockets can be very persistent.

__________________


Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

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was it overheating before first t-stat replacement?


from the description above it seems that you have a clear "air pocket"
situation but you might provide additional info considering the coolant
type and mixture.

which temp you consider as too warm,..I know several of those engines
running perfectly well on steady 85C or even 90C,...the point is that you
dont get high temp sudden spikes.

filling upper rad hose as described above is helpful and you might want
to warm up engine and place the car on ground so the nose is raised
for a few inches,....open coolant rad/jar cap,full heat ON and keep it running for several minutes like that.

you did mention you dont have a heat,...which points to monovalve or
stuck pipe (depending of a setup you have) problem or restriction due the
air pocket.

drilling the holes (IMHO) will not resolve issue but will give you longer warm up times,...more engine wear..lower mpg's....etc...


cheers
ChO


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__________________
w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered

This doesn't address the no heat situation however you do want to make sure the thermostat is correctly installed. No need to ask me how I know this causes an overheat condition....

__________________
1985 300D 172,110mi and goin' strong

You have air trapped in the heater core.

Next time:
#1. Disconnect the upper coolant hose from the radiator.
#2. Cap the radiator upper hose fitting (duct tape is OK).
#3. Remove the mono valve repair kit.
#4. Remove the coolant cap.
#5. Pour coolant into the upper hose (use it as a funnel).
#6.
#7.
#8.
#9.

Urgent biz, back in a while.


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__________________
ASE Master Mechanic
https://whunter.carrd.co/

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1985 300SD
1983 300D
2003 Volvo V70

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