The OP writes that when he did open the radiator cap again he got a blast of hot water and steam. That move has sent so many people to the hospital for burns. ALWAYS LET THEM COOL OFF AND BE REALLY CAREFUL WHEN WORKING AROUND OVERHEATED ENGINES! When you think it is cool enough, even then be very careful and try to hide the cap under rags -ect. while you slowly remove the cap. Less dangerous but still risky is adding cold water to an overheated system. That cold water will go directly to the head and crack it, so be cautious when adding water.

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Junqueyardjim
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important. C.S. Lewis



1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!

that is a possibility, but it's unlikely with steam present. water exits the top neck on a 240... hmmm if the radiator was frozen solid, or at least the lower portion of the tubes were frozen, it would be the same issue as a stuck thermostat. good call.

I also agree that steam = don't drive.
I also agree that steam = don't open the radiator cap. I've done it, and I've gotten severe burns as well. I usually do it with a towel and only open the cap to the first detent to let steam escape before I remove the cap and get a steam and hot water bath...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

the safest thing to do with an overheated engine is to slowly put water on the exhaust manifold until IT stops boiling the water you are pouring on it, then slowly migrate the water to the block of the engine until IT stops steaming up the water you are putting on the block. and only THEN would I recommend attempting to open the radiator or put any coolant INSIDE the radiator!
a heavily overheated motor will easily shatter if water is presented to it's internal surface.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Yeah, the "first detent then wait" is what I did - should have been more clear, had many a car overheat and never burned myself yet. The water was put in at a very slow trickle, but whether anything was damaged I won't know until the t-stat gets installed. As for a "frozen block"...that's not going to happen in my part of California!

So I installed my new t-stat tonight, and while filling the radiator, noted the cap read "13 psi". The section I was using, 20-110 ("Removal and replacement of coolant thermostat"), mentions pressure-test to 1 bar. I looked a little farther, and page 3 of 20-005 says "gage(sic) pressure of approx. 1 bar in cooling system".

Since 1.0 bar is actually 14.5 psi, I wondered if I did need a higher rating, but many parts sites listed "13 psi (SAE Range 12-16 psi)", and none of the suppliers to US cars had it any differently (although EU cars have either 0.9 *or* 1.0 bar ratings), so it looks like no replacement needed.

Now that everything is back together, I am going to take him out for a run tomorrow and see what happens, then drain and add 50/50 coolant (about 1-1/2gal each) if I don't see any problems (esp: leaks!) He started up like a champ tonight, but at-speed will tell...

A short drive proved I am still overheating, so here is where I stand:

- radiator intact
- new thermostat in place
- top radiator hose hot, bottom one cold

so I am back to thinking the pump itself is dead. Even if the heater core *is* busted, the lack of any pumped coolant may explain the lack of a leak (yet).

Other than replacing the water pump, any other leads?

I took out the water pump today and it appears fully functional: no bearing noises, spins easily, all the vanes intact... So I have no idea where else to look - just to recap: radiator intact, new thermostat, water pump intact, but no heat into lower radiator hose. I forced water into the opening behind the water pump, and the block seems to fill up, because I then get water out the higher opening.

I'm at a dead-end now...

if your car is indeed overheating, and your lower radiator hose is cold, your radiator is not flowing coolant through it. get an infrared thermometer and go get the car hot. then pull over and measure the temps accross the head at each injector, and at each glow plug, see if any of the temps match the thermometer reading... youmay have a bad coolant sensor.
if the head is sitting above 175F, or above 210 or so, and the bottom hose is cold, water is not flowing, measure the temps in the radiator, pop the shroud off, and use the thermometer to measure across it 1" at a time, side to side, top to bottom.
you may have a bad thermostat still, you may have a plugged radiator.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

So I tested the radiator for blockages and it flows freely. I also pushed water through the heater system and it has no leaks and flow runs through the block all the way to the lower inlet of the water pump with good pressure, so I am wondering if the water pump can look intact but still not work. I have the car back together and will take it for a drive to see what happens.

If it keeps overheating, I will have to change out the water pump.

Removed the radiator and found a leak at the top of the radiator (had to turn it on its head to finally see it), so more likely to cause pressure leakage while running rather than fluid leakage. I have a salvage one on order, and will also be replacing the pump and its housing since I twisted off a couple bolt heads getting the pump out of the housing, and I don't want to try to fix "damaged goods" with my lack of skills and tools.

I'll bolt everything on as it comes in and maybe this will solve the problem...

So it's been awhile - I changed out the radiator, the water pump and its housing (the old one broke off 2 bolts when I tried to get the pump out), and the thermostat. Still goes to red line within a mile of driving, so today I tried taking the thermostat out "just in case", and the same thing happens (including the cold lower radiator hose). I noticed a drop of water on the pump, which may have come out of the weep hole, but I couldn't be sure. I am at a loss, and may just sell the poor guy to someone more mechanically minded...

What's funny is it runs like a top - starts up easily, purrs along smoothly, accelerates as well as this size of diesel engine can, and no problems at all from the 4-speed manual -- if it wasn't for the temp gauge and the steam coming out the overflow tube, you wouldn't know anything was wrong!

Are you making sure you have the coolant topped up when filling it? You have to fill it and run it long enough for the stat to open then fill again to get all the air out. Also are you sure you got the stat in the right direction? if it is upside down it will not work right at all.

Removing the stat will make it not function correctly and it will run cold when the weather is cold and hot when it is hot outside.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

change the radiator cap.
Tom

The weather has been mild, so running without a stat shouldn't be an issue - without it is the same as a fully hot engine. I will double check fluid levels in case I missed that, but I remember getting it to overflowing.

2 different caps, same result. No steam escaping from either, but when the gauge was in the red, I did see steam out the overflow tube - kinda weird seeing it come out of that, far from the cap and pointed down!

Why do you think hot upper hose and cold lower hose is a problem? That's the way it's supposed to be.
Try swapping out the temp sensor.
MB thermostats are bypass thermostats. Removing them will not cause the engine to run cooler.

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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