Hello fine folks,

I am very happy to see such a community in existence on the net!

I have a problem, as some other seem to as well. Only thing is, it happened suddenly.

I bought an '83 300sd from charity auction (pix below). She is so nice, but the first few days I drove her, it seemed like she was losing water from an unknown cause, but was not leaking. I put some bar's leaks pellet sealer in and things seemed to be normal for a month or so. (80 deg. Celcius, constant.)

Just 2 days ago, I had to turn the AC on, driving back from a 50 mile trip. It was hot, and although I knew my compressor was bad and noisy, it still worked, so I used it. Figured it would give out and I'd buy a new one. I drove for 30 miles, no problem. But as I got to the toll booth, I shut the AC off, and the temp. instantly shot up to 110, 120. Perhaps there was too much stress on the motor with that impaired compressor.

Long story short, I replaced the lost water, and bled the system. I even tore off the ac belt, thinking maybe the compressor had seized. Now, The car will drive fine for more than 50 miles on the highway at 60mph as long as it has fresh water in it and you don't stop. But once you stop, the temp. shoots up and won't come back down unless you turn the heater on. Even then, it is not within normal operating temperature. There are no leaks from anywhere, just pressure building up and water spraying out of the pressue valve on the expansion tank cap, slowly. The water stops coming out when the car is turned off. I have bled the system, following the procedure to plug the small return hose from the reservoir, and then squeeze the top rad. hose, to fill the bottom one. Seemed to be the fix, but then I found that it still overheats after 30 or so miles on the highway.

Could this be a thermostat? Clogged Radiator? It's strange because it has been overheating ever since that day I turned the AC on for 10 minutes. In fact, I had turned the AC on before, just not in such hot weather. (90+ degrees)

I am about to change the thermostat, cap, and possibly the pump. I am hoping you guys may be able to shed some light on the matter. It would truly be a blessing, as this is my only car and I need it to get to work every day. I am mechanically competent, and can do anything basic to semi-expert to a car. Any suggestions?

THANKS A MILLION!

-Rod R.

Welcome to the forum.

There are so many possibilites here that I don't even know where to begin.

The fact that the engine was burning coolant with no obvious leak is a telltale sign of a blown head gasket on the 617. Putting Bar's leak into the system really complicates matters because it restricts the passages within the radiator and that radiator has very tiny passages to begin with. So, the use of the Bar's leak may have compromised the radiator to the point where it won't function properly at low speeds.

In addition to the possible clogged radiator and possible failed head gasket, you've got a fan with a clutch that should engage fully when the temperature climbs up above about 105°C. to force more air though the radiator. Additionally, there is an electric fan that will also come on at high speed just for those occurrences where you've come down from a high speed run and the engine has no airflow. The question begs whether one or both of these fans are not functioning properly.

There's a lot of work to get this vehicle back to proper operating condition.........and that might entail removal of the head and replacement of the gasket. Ignoring the problem will definitely cause the bearings problems in the long run due to coolant contamination of the oil.

The gasket failure is a relatively common problem on older 617's. This one suffered the further indignity of a cracked head. The characteristic loss of coolant with no visible leak with confirmation of an oil analysis leaves no doubt about the problem.

Upon checking the oil, there does not seem to be the smallest amount of antifreeze or water present. In addition, it does not smoke at all. I just can't fathom the head gasket being bad without these symptoms, On top of that, since the car just started overheating after the AC fiasco, I would think it should be something else?

Maybe I'm just scared of a head gasket replacement!

The bottom radiator hose is generally cooler than it should be, which makes me think there is not adequate flow through the radiator. I'm going to change out the thermo. tonight. I'll keep you folks posted.

Appreciative,
Rod R.

You'd accomplish more by getting a new cap for the tank.........if the cap is truly bad. If the cap is working properly, the system is building too much pressure.........another sign of a compromised head gasket.........or a cracked head.

The tank has a hose beneath the cap that directs the overflow coolant toward the front of the vehicle and down to the pavement...........so there should be no "spraying out of the pressure valve" under any circumstances.

Good looking SD BTW.........very clean body and exterior........

I think you should stop driving it immediatley and sell it to me. Better yet, pay me to come take it away.

It looks sweet!

I don't really have any advice for you, but I would say that it is a keeper! Keep at it, you can figure it out.

Good luck,

Jim

__________________
1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.

To your experience, would a clogged radiator cause pressure buildup? Also, could a BHG exist without any changes in oil condition or exhaust smoke?

I don't smell any diesel fumes in the ex. tank, but maybe the HG is blown around the exhaust area, causing the lurching?

Wow. what a weird issue. My other car did the exact same thing, and it was a 1988 Sterling. Happened when I changed the coolant, following a starter motor replacement. (had to drain the hoses to get to it) Never figured the issue out, and sold it at an auction.

ARRGH! it's always the thing that drives me the craziest and has the most possible causes - overheating!

\Thank you!
Rod R.

A clogged radiator will not cause excessive pressure. It's restricted in flow.........not completely clogged.

There is possibly a change in the oil.........you just cannot see it.........but an oil analysis will confirm it.

Diesel fumes in the exhaust are not characteristic of a blown head gasket or a cracked head. Consumption of coolant and excessive temperatures and pressures are characteristics.

If you don't bring it under control with a change of radiator and/or restoration of one or both fans, then have an oil analysis done........it'll tell the tale.

you havent answered the two points brian posted about the fans. Are your aux fan and engine fans running???

__________________
Mike

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1975 200 - Sold (no pix);
1978 200 - Sold - http://www.pbase.com/hboy/redbaron
1979 300TD - Sold
http://www.pbase.com/hboy/greenwagon
http://www.geocities.com/hboy726/300TD.html
1985 230E - now my daily driver...

By the way. I think the 126 looks really neat with 116 hubcaps. First time I've ever seen a car with retrofitted caps like that but I like it.

- 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

I've had similar symptoms on my MB 300SD 1982, check you're radiator, easy to pull and if your careful, easy to have inspected... I noticed that you said lower return hose is cooler than top supply hose, this could be because of restricted flow through the radiator, was in my case. Ended up replacing radiator, however, due to necessity of daily driving, did not check the cause of radiator problem, you can get loss of coolant that looks like overflow from bottom weep hole in the water pump, also, good idea to check thermostat and thermostat housing seal. I know this sounds like a shotgun approach; however, if I had approached my problem as a system problem and not a "failed component" problem, I probably wouldn't have blown my cylinder head, over $2,000 for head, parts and tools...

Damn & blast - so I need to get my oil tested to confirm this?

My symptoms are

- slight loss of coolant on some longer driving trips
- sometimes there is pressure in the coolant expansion tank after the engine has completely cooled
- no visible coolant leaks or drips onto the garage floor

From Brian's comments sounds like a poss head gasket.......

I've put about 4,000 kms onto the car in the last 3 months so the signature is wrong at this stage. 1983 300sd.......

pop the rad cap off, release all pressure, on COLD motor. put cap back on, and start the motor. does the pressure build up in less than 1 minute? bad head gasket.
no pressure? ok, take off the cap and look for bubbles. are there any? no? ok, pinch the small hose off, now are there any bubbles?
John

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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!

Hey folks, Ok, so last night I took the thermostat out. I disconnected the hoses to and from the radiator, opened the petcock and saw that there was what seemed excellent water flow. A garden hose at full power was stuck in the top hose, and there never was a point where it over flowed at the top... only the bottom and petcock.

In response to the car building pressure up in less than one minute: No. I drove the car for 20 minutes last night before the pressure started building up tot the point where it SLOWLY! started coming out of the expansion tank pressure hose.

I do see the water level rising slowly when the cap is off, and spilling out of the pressure relief hose, but not really any small bubbles.

Wow. I am really starting to dread anything past this point. Any suggestions? I'm going out right now to buy a new rad. cap.

THANKS A MILLION!

Rod R.

BTW, thanks for all the nice comments about the car. I will put up some interior shots as well. Shame that this car should have to act like this....

Well at this point I would send a sample of oil out the the lab, and see what they say. It really sounds like the head gasket.


How old is the cooling system? Personaly if it were my car and I planned on keeping it I'd replace the radiator, all the cooling hoses, T stat, expansion tank cap, probably the water pump. Then flush and clean out the whole system, now you have a base line. Then you are good for a long time, and can run the AC all you want without having problems.


Nice car btw it looks like its worth putting money into.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Can't the coolant cross over into the automatic transmission through the ATF cooler?

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'83 300DTurbo http://badges.fuelly.com/images/smallsig-us/318559.png

Broadband: more lies faster.