The thermostat housing on my 85 300D looks like this- but on my 240D it has some sort of vacuum fitting with 2 vacuum lines. What does this accomplish?

I hope you're using a [proper coolant / water mix ~ my '82 240D also uses coolant, I keep saying I'm going to add an overflow tank but never get aroutuit .

There are several places that the cooling system can clog when you use plain water, I learned this when mine failed in Rhyolite Nevada (look it up for a laugh) .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

How could something in the cooling system clog with plain water and not with 50/50 coolant?
But, yes I have an anti-freeze/water mix in there.

What it seems like is that maybe the thermostat is closed and not allowing circulation. I think thermostats usually fail the other way- they stay open and cause the engine to warm up too slow.

What else could cause a lack of circulation? My son just took it for a ride again, driving slow on back streets for 15mins. The temp gauge never came up, but reported steaming. After it cooled down, I checked coolant level and it was at the top.

I replaced the water pump on this car 1.5 years ago upon getting it on the road for the first time in 16 years. I see nothing coming from the weep hole, so I doubt the water pump has failed again. What else could clog the cooling system? Monovalve?

Again, it sounds to me like there is no coolant in the block. Remove the top radiator hose connection (cool engine of course) and pour coolant in the hose. You should be able to get at least a half a gallon in.

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All Diesel Fleet
1985 R107 300SLD TURBODIESEL
2005 E320 CDI (daily)

LOTS of parts for sale!


EGR block kit
http://www.peachparts.com/shopforum/diesel-discussion/355250-sale-egr-delete-block-off-plate-kit.html

1985 CA emissions 617 owners- You Need This!
Sanden style A/C Compressor Mounting Kit for your 616/ 617 For Sale + Install Inst.

Sanden Instalation Guide (post 11):
http://www.peachparts.com/shopforum/diesel-discussion/367883-sanden-retrofit-installation-guide.html

I'll try again, but when I remove that top hose from the radiator a lot of coolant comes out of the radiator and the hose. In other words, it seems to be completely full. Maybe I'll put a catch pan under it and try again and see how much comes out.

At this point my suggestion would be disconnect both the top and bottom radiator hoses. Let everything drain out of everywhere. Put a garden hose into the top hose and turn it on, if not full at least a decent rate. See if anything comes out of the bottom hose.

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

Here is the latest.
Today, I removed the thermostat. I put in boiling water and it opened up just fine, and closed when cooled down.

I determined that the temp gauge issue is the electrical connection to the sensor. If I ground the wire, the meter pegs. I attached with a clip lead to the sensor, and it does in fact read correctly.

So- I'm going to put in a new tstat just because, drain the system, put in a new drain plug, which has broken off, fix the sensor connection, fill the system and drive a bit to see if it overheats. I was advised to also pressure test the cooling system. Not sure what that entails.

It means you need to hit up some pawn shops until you find a pressure testing tool, it's like a radiator cap attached to a hand pump with a gauge .

It should come in a box with adapters to test various types of pressure caps too as they wear out far more frequently than most realize .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I might run the engine with the radiator cap off. Watching for any evidence of head gasket failure. Do this from cold of course as no joy in being scalded.

You checked the thermostat out and it is okay. Something is creating excess heat generation or it has warmed up a lot in your area and the cooling system does not like it.

You also changed the water pump and it might have a problem. Killing adequate circulation. A test for pressure differential may be indicated.