1975 240D, Could it be head gasket (please god no) - PeachParts Mercedes-Benz Forum

PaulVNunan · #1 05-05-2006, 02:39 PM

An epic tale of bravery and overheating....
We start our story in the gentle mountains of Western North Carolina, where my 1975 240D, Oskar, likes to overheat at stop signs and traffic lights.
Once on his way again, Oskar rides smooth and cool at 175.

So, in a long story cut short.
One flushed radiator, new thermostat, new sending unit, new water pump later,
still overheating at idle, but runs cool at highway speeds (35-55mph).

3 mechanics said probably a head gasket leak.

The thing is, I not leaking any fluids, and there doesn't seem to be any fluids where they are not supposed to be.

Could it possibly be anything else? Is there anything I'm overlooking?

P.S. This problem has only started about 2 weeks ago, and I'm not noticing any change in drivability.....

Thanks for Advice!

Paul Nunan

rg2098 · #2 05-05-2006, 02:45 PM

Are you loosing any coolant?

Diesel Giant · #3 05-05-2006, 02:49 PM

In my 25 plus years or wrenching on cars and taking with radiator shops, the only way to get a radiator clear of calcite deposits is to use the acid treatment. "Flushing" is fine to get old antifreeze out, but does nothing if you have hard deposits. It is like granite in the radiator and will never come out with a traditional flush. So you still need to address the radiator, either take it to a shop to get them to flush it or drop a new one in.

Then reevaluate.

PaulVNunan · #4 05-05-2006, 03:24 PM

Yes, i should have been more specific, the radiator was soaked in acid, at a shop, and no, I don't seem to be losing any fluids at all.
It's one of the reasons I'm stumped...I doesn't seem to me to be a gasket problem, I haven't noticed any change in the way the car drives, smells, sounds or feels, save for the overheating problem (which is a big one to me)

OMEGAMAN · #5 05-05-2006, 03:37 PM

How hot does it get at idle and how long does it take to overheat. Does this happen with the a/c on or off. It might just be the cooling fan clutch is no good anymore allowing the fan to idle rather than spin. At highway speeds you no longer need a fan for effective cooling.
One more thing. Verify the engine temp with another guage. The one in the dash may be doing weird things you never know.

Diesel Giant · #6 05-05-2006, 03:57 PM

Go to NAPA and get a block test kit. This will allow you to check and see if the head gasket is blown. Comes with a suction bellows and some blue fluid. I use to use them when I did head gasket repairs.

Very acurate.

wheelguru · #7 05-05-2006, 03:57 PM

Drive it a few miles and then shut it off, get out and see if the radiator is hot at the bottom. I went round and round with running hot on my '78 300d. When I felt the radiator, it was always cold at the bottom, hot on top - there was no flow through it. I ended up drilling a couple of holes in the thermostat. it did the trick. You might want to refer to the other overheating post from today, and look at the diesel giant site for his take and excellent pictorial about drilling out your thermostat. -Andy

Diesel Giant · #8 05-05-2006, 03:59 PM

Here is the pictorial on the t-stat mod. Use this after all else has been tried.

http://dieselgiant.com/thermostatreplacementandmodif.htm

PaulVNunan · #9 05-05-2006, 04:05 PM

At idle, it redlines, within 2 minutes.

The fan on this model is a straight shaft, no clutch, and pulley and fan are tight.
Thanks for advice, Diesel Giant, I was told there was no way to test the gasket for leaks other than to look at it physically. By the way, great site, I used it just last week to fix my odometer, I hope I can continue to use it......

While I was testing all options, I did run the car without a thermostat alltogether, and it overheated anyway....

The reason the radiator mechanic gave me the head gasket verdict, he said that the coolant system (radiator) was pressurizing too quickly. He said that the compression from the engine was traveling back into the system.

The reason I am hesitant to swallow that diagnosis, wouldn't the car run very poorly if the gasket was that damaged?

PvN

Diesel Giant · #10 05-05-2006, 04:09 PM

3 ways a head gaseket can manifest itself. Oil in the water, water in the oil or exhaust pressure in the cooling system. Unfortunately your mechanic was not pulling your leg. I have seen more cars pressurize the coolant than any other type of failure. And yes your car can run fine and exhibit this problem.

vstech · #11 05-05-2006, 04:23 PM

with a head gasket blown... sorry.

with cool engine, take off the radiator fill cap and watch the fluid. if it bubbles you have air being pumped in from the head. budget a HG repair, or a transplant motor.
John

PaulVNunan · #12 05-05-2006, 04:25 PM

So, even if the head gasket leak/damaged head might be so slight that no liquids are misplaced or leaked, This block test (which checks for combustion gasses in the radiator fluid) can detect even the smallest of problems?

Diesel Giant · #13 05-05-2006, 04:39 PM

Normally yes. As the previous post states. With the car stone cold, take the rad cap off and let it idle and rev it up. If you see coolant start to gush out, that is exhaust pressure in the cooling system.

Not a huge deal to do a head gasket.

PaulVNunan · #14 05-05-2006, 05:14 PM

Maybe you'll post a how-to on your website....

I guess I'll have to spend some more cash on this kit to know for sure, I mean, if the radiator test doesn't prove positive...then I've tried everything....

t walgamuth · #15 05-05-2006, 05:34 PM

i think if it were a head gasket it would heat up while driving too.

do you have your fan shroud in place?

tom w