I don't think he understands that the upper hose connects to the head inboard of the thermostat.

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Since you clearly don't wish to follow our suggestions........maybe you've got one of your own that you'd like to try?

If so, let us know how you make out with that.

I didnt say i wouldn't do it, i'm waiting for the car to cool completely. Craig, i understand how it works now in there, i've never seen a setup like this.

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It's called a bypass thermostat system. It doesn't work like most systems in US cars which block of the flow of coolant through the block until it warms up. MB's circulate the coolant through the block until the engine heats up and then the thermostat forces water through the radiator and not the block anymore.

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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

If overheating persists despite filling the head via the upper radiatior hose, suspect the thermostat. I went thru two garbage Behr T-stats prior to buying a Stant T-stat at Advance Auto Parts, which then allowed my car to run at the proper temperature.

The thermostat doesn't decide to take a dive at the precise moment the radiator hoses are changed..........it's not that brilliant.

Does the 240 have a fan clutch? It seems that going down the highway and cooling to 90, even though warmer than it should be, could be an issue with not eneough air across the radiator when going slow?

Brian has had a alot of these fixed by doing this, maybe this one is a differant issue? is there a hole next to the t-stat on the 240 like the 300sd? maybe drain it some and refill through the radiator hose?

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83 300SD Dark Silver Dark brown inside

When I filled mine through the upper hose, I kept filling until the coolant started coming out the rad where the hose would go. Then I put the hose on with just a bit of it open so I could keep filling. Then finished putting on the hose. Still had some burping to do, but it seems good now.

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Ginny in Denver-ish
78 300SD, 265K (mine)

No, the 240 does not have a fan clutch..

Long time no hear from you, leathermang. Hope all is well.

The reason water gushes out when the engine is warm and still not completely full is the air inside is now hot and wants to expand. With no where to expand it, along with the steam from the boiling of the coolant, pressurizes the closed volume of the coolant. You open a path, anywhere, and either hot air and vapor will come out, or, if the hole is below the water line, water will come out. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

opening up the heater valve by running the heat full blast may get uncomfortable, but I've found this method works very well since it allows the head to have more than one open passage to circulate coolant in. It needs a high RPM like a couple of miles down the freeway to do this and yes, a Stant thermostat is what I would use too. Makse sure you have no leaks, turn on the heat when you leave the driveway and keep it on full and go. I've never had a problem burping this way!

Thanks Jim....I had to take a break...

I think this is a good time to bring up something about overheating in general on 20 plus year old cars...

In the old days when someone rebuilt a block they would take everything off of it...and take it to a place that would boil it out... it would be really clean everywhere... but the part that mattered most in the long run was inside the water jacket of the block ( head counts too ... but focusing on block here)... there is a place typically at the lower back part of the water jacket where the flow rate slows down and stuff is deposited over the years.... and often on these heavy blocks you hear of people renewing sleeves, pistons, rebuilding head...and heading into the future thinking they have a new engine...

Then some summer arrives and they see slowing climbing temperature readings.... and they do all the 1st and 2nd level cures which people suggest....and sometimes that works... but sometimes the fudge area has been taken up by the lack of cooling at the lower part of that old block and those fixes don't work...

If the other stuff does not work.... I suggest taking out the freeze plugs and making something which can be pointed into the lower corners of the water jacket while suctioning water out at the same time... I say it this way because you can't just let the water get into the way and still have enough turbulence and pressure reaching that area of crud.... and it may need to be at the same time as an acid flush happens....and it may need to be done repeatedly to be successful ...
Greg

Ok all this was done twice. Head will NOT take any more coolant through upper radiator hose.

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Ok...go test it and report back....

Okay, I was wrong, I'm not fixed.
I was on the hwy today and the gauge went to 110. I turned on the defrost to get some of the heat off and it went back down to 100. Driving more, the gauge went to 90, up to 105, down to 85, up to 100. No rhyme or reason to the fluctuation.
The gauge just goes up and down, with the heat on, with it off, at high speeds at lower speeds.
When I got home I unplugged the mono to default to highest heat and let the car idle. It went back down to 85 with the defrost on (mono unplugged) and when i turned it off the heat the gauge is creeping up slowly. 8 minutes or so and still at about 95.

The good news is the WVO tank is now showing 152*. Which is the reason I changed the tstat in the first place, the car AND the oil couldn't both heat up before. Gauge would show 65-70 and the oil would show 100-105. When the heat was turned n the gauge would drop and the oil temp would drop. (all oil references here is WVO not engine oil).

Should I jack up the front of the car to get the head higher or put in another tstat?
I'm on an incline now but maybe not high enough?

The tstat came out of the parts car. It's new too, and the DH told me this morning that his car always ran right around 100* since no one told him that was kinda high he never through twice about it. Shop did his tstat, not him. So you think the tstat is bad?

Thanks

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Ginny in Denver-ish
78 300SD, 265K (mine)