Hey all,

So my '83 240D has been running perfectly for the last few months with no overheating issues or leaks, however yesterday while sitting in a drive through I watched the temp gauge climb to about 105 C. Kept an eye on it and once I drove away it cooled off back to normal operating temp. Then this morning there were two small puddles of coolant under the car. Some coolant ran down the exhaust dripped and there was another small puddle under the thermostat housing and water pump. There was fresh coolant on the hoses connected to the thermostat housing, so I tightened down the clamps as they seemed looser then they should be. Coolant level seems ok however. Is it possible the water pump is going out? Not leaking from the water pump as far as I can tell. I just don't see how losing only a little coolant through a loose thermostat housing hose could cause it to get hot so quickly. Thermostat was replaced about 6 months ago, no idea when the water pump was last done.

You will know soon. When I first got my Car I found that there was deep pitting under the areas where the hose gets clamped on the aluminum parts. No clamp tithing was going to fix that.

If you can't see leaks when the engine is cold and not running you nave to feel for them

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84 300D, 82 Volvo 244Gl Diesel

Much easier dissipating heat when you're moving. Air's coming at you, fan is spinning faster, etc.

Were you running the AC?

Have you figured out where the coolant came from?

Is your water pump making any noise?

Unless you've lost a bearing and the impeller isn't spinning, it's unlikely to be your pump, which means it's doing its job moving coolant. The next link in the chain is the radiator, whose job it is to cool said coolant. Then there's the thermostat which, etc etc etc...

You've got a 240 so no fan clutch. It sounds to me like a marginal radiator, though I'd want to be absolutely sure I'd isolated and eliminated the coolant leak before you go chasing more exotic points of failure.
There's always the possibility of a faulty thermostat (I had one fail after a year), though you'd likely be seeing signs of that at speed.

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1981 240D 4sp manual. Ivory White.

I was not running the AC since it's not functioning at the moment. It looks like the coolant is seeping out from the hose connections to the thermostat housing. Water pump does not sound like it's making any noise.

I don't say that the problem is your pump, in fact there's a good possibility that it's OK. It can however leak without making bearing noise. There is a weep hole in the area aft of the pulley that is designed to allow coolant to exit if the internal impeller seal goes kaput.

From your observations, the hose clamp may have been the culprit, but have you checked the gasket sealing the thermostat housing? Most new thermostats come with a gasket, but there are some extremely thin gaskets and others better that are thicker. I have had times when I had to replace the gasket supplied with a new thermostat with a thicker one due to leaking caused by a thin gasket.

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Don't Chrome them; polish them

I did tighten up the hose clamps, and it is possible that this is the only place it's leaking, but how would it cause the car to get hot at idle if it has lost hardly any coolant? Thermostat housing mount seems dry, only wet near the hoses. Radiator also looks to be in good shape as well.

It wouldn’t.

Losing coolant pressure should only lower the boiling point of the coolant.

Re: radiator looking good, not sure how well a visual inspection of the exterior and the 2 inches of filler neck will serve you.

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1981 240D 4sp manual. Ivory White.

I'm not as familiar with the 240D but on a 300D you have to be sure and get any air out and burp the system properly after any leaks are remedied, or after a coolant fluid change or it can overheat at idle.
Also I have seen the temp gauge in the cluster go bad and show high temps when the temp is actually normal.

Installing a new radiator fixed a similar problem in my 1985 300D, though I had no coolant leaks. I had tried many things before that over several years - Tstats, water pumps, many flushes, another used radiator.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

If your radiator is original then you need a new one. They don't last 35 years.They corrode and lose a lot of efficiency with time.

If your car has a coolant leak then you need to fix it. Any coolant leak will substantially lower the cooling performance of your car. I am not sure why but I had it demonstrated to me that if you put a leak in a perfectly running car, then you will make it overheat much more easily. Don't believe it? Then repeat the experiment and draw you own conclusion.

Under pressure the coolant boils at a much higher temperature. So any leak point that removes pressure lowers the boiling point.

As the fluid comes up to temperature it creates expansion of the coolant. creating the pressure you need. At 105c indicated. If a leak let the pressure escape. The radiator cap valve would open and spill some fluid out the line from the neck of the rad. in a tight system. Your leakage point served the same funtion.

Normal test is to get a system pressure tester. You pump it up and see if the system holds pressure.If there is system leakage you will see where it is as well. Also of course if it will not hold pressure. With that out of the way. You then try to find out why it got that hot to start with. Old radiator is always one possible suspect.Yet not the only possibility.

My apologies for this comment in my post. It seems rude in retrospect. It sounds as though I am challenging the reader. No challenge is intended!

Very first thing to check is the color of the coolant, often it's muddy and do won't transfer heat well .

The next thing to do is a proper cooling system cleaning, use Citric Acid and water, no need to buy the $pendy Mercedes Citric Acid, it's cheap at baking supply stores or on E-bay etc.

Once the system is clean your heating issues should end but very often lack of proper maintenance over the decades meas corrosion between various alloy parts and rubber or the engine proper .

Any visible cracks in a hose, no matter how tiny, means the hose is kaput and time for a new one .

The thermostat uses an O-Ring to seal not a gasket .

Quite often when there are coolant leaks the two facing machined surfaces are corroded, you can repair them by polishing the pitted surface against a piice of window glass using 1,000 or finer wet/dry abrasive sheet .

Last time I checked Mercedes still sold all the OM616 hoses and alloy housings your 240D might need, better than repairing the old pitted ones but you might now have the $ to buy new .

Remember : any time the temperature gauge begins to rise, you can and should turn the heater on ~ you needn't turn on the fan if the hot air from the dash vents bothers you but the heater core is a good little radiator but itself .

NEVER run the AC if the engine's to hot

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-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

An infrared thermometer is good for locating blockages in a radiator, they show as cool spots where the hot coolant cannot pass through and/or is restricted and transfers less heat.

As stated, if it's a 38 year old radiator it would be best to replace if it shows the slightest blockage or leakage. A new radiator makes a BIG improvement in cooling.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Interesting…

Is it possible to have a 38 year old original radiator, well cared for, leak free, sludge free etc, that has still lost efficiency?

From what I’m gathering, these things experience internal corrosion no matter what.

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1981 240D 4sp manual. Ivory White.