Over heating on highway in summer 1980 w123 300d

[123mike]

Had something pop up on a 90 mile drive at 70mph in 92 degree summer heat. My old 300d started getting hot , temp gauge above 100. Pulled over, let car run, turn the manual heater on. Water level ok, The Temps fell to 90ish. 45 miles to go, running 60 mph, it stayed under 100 degrees, hot as hades inside the car with heater on.

I get near home and check things again, engine is sounding more rattle than usual, l pour maybe a quart of oil in and Temps fall to normal. My last 10 miles , the Temps are in 85 degree range. Oil pressure was always strong and I topped oil to mid dip stick line before trip. The morning 90 mile trip was fine, outside Temps were 78 degrees

Will low oil cause over heat? I'm pretty certain I had oil.
What would the rattle sound be? Seems like i heard it around timing chain or around altenator.
My radiator clogged up?
Or everything is fine, and I have heat stroke?
Or I blew my engine.?

[engatwork]

How old is radiator? I'm not sure I wouldn't pull it out and have it cleaned out or just replace it.

Low (and too much) oil probably can create elevated temps.

[5cylinder]

Originally Posted by engatwork

How old is radiator? I'm not sure I wouldn't pull it out and have it cleaned out or just replace it.

Related true story pertaining to my 1983 300D:
In 2011, I somehow got the idea (likely from someone on this site) to replace the radiator not because I suspected that it was failing but because it was original - 28 years old - and as a friend at M-B corporate once said to me about another old original component on the car "You've gotten your money's worth."
I also feared a catastrophic engine failure if the radiator failed while driving.

I acquired a new Behr radiator and planned to install it over the upcoming weekend.
I pulled into my garage after driving home on the freeway and as I walked by the front of the car to enter my home, I noticed that the grill was wet and there was a hissing sound coming from the front of the car. The original radiator had sprung a leak during the drive home. Thankfully, the temperature gauge showed normal and there was still fluid in the reservoir tank.

[Sugar Bear]

Sticking thermostat and/or bad radiator. If the oil was low enough to increase the coolant temp that's really not good, I doubt that was the cause vs pulling over.

[123mike]

Thanks for the input! I woke up with a feeling of dread. Did I murder my 300d ? I recently, had the air filter removed for a control rod bushing, made room to enlarge hole for coil compressor,

Took it off again and made sure everything was buttoned down.

The Alt is held tight with a wedge of wood that was missing. A new wedge fixed rattle.


Next step, is it safe to run some radiator cleaner Chemical in the system? It is a rusty colored liquid in the radiator. I use antifreeze and flushed it 7 months ago.

[vstech]

The next step is CHECK THE OIL LEVEL...

[engatwork]

You probably need a radiator.

[vstech]

If you have rusty fluid, you need to flush out the system.
Sediment likely got loosened when you flushed it last time.

I would start with a garden hose in the heater hose with the water tank cap off while idling for about 20 minutes.
It should flow clear after a bit.
I like the prestone kits. They work out fairly well.

After the water flows clear a good 5 minutes, dump some cascade in the radiator and close the cap.
Run THAT for about an hour on the road.
It will remove all traces of oil in the system.

THEN you can do a citric acid flush.

Then you need to do the garden hose flush for another 30 minutes...

If nothing is leaking after all that, it should be safe to drain it all down and fill with distilled water and zerex g05 coolant.

[Marshall Welch]

I wrote up a reply earlier today, but it looks like I didn’t hit the submit button.

At the temperature that your engine appeared to have experienced, I think the valve for the oil cooler hoses would have opened. I forget what the opening temperature is for the oil cooling system, but my recollection is that it occurs at a higher temperature than the usual operating temperature.

As others have mentioned, there are a few possibilities, including the radiator, thermostat, and possibly the water pump. It seems reasonable to try a cooling system flush, with a de-oiling step as already mentioned, followed by a flush with 10% citric acid. There’s also another cooling system flush product mentioned here recently that was reported to be very effective, but I don’t recall the name.

The recommended replacement interval for thermostats is every 6 years. I recommend Behr (original equipment brand), Genuine MB, or Wahler (another excellent brand, possibly OE, but I’m not certain). I won’t vouch for other brands.

My impression is that more than a few of us here think that replacing the original radiator is a good idea, given the age of these cars. Behr (OE) and Nissens (Denmark, NOT the Japanese Nissan) are both excellent radiators. I replaced the original Behr radiator in my car with a Nissens radiator 2.5 years ago, and have been very pleased with it.

The water pump is another possible culprit. I would try to find out if the original water pump has been replaced. If not, I would check around it for coolant leaks, and check for any play in the water pump fan/impeller shaft by wiggling the fan back and forth. If replacing, I would use an aftermarket brand from Germany, or Genuine MB brand, but the prices I’ve seen lately for Genuine MB are steep, I suspect due to the current market conditions, ie, tariffs.

Good luck!

[Sugar Bear]

X2 on Wahler, Behr or OE thermostats only.

I prefer CRC ThermoCure flush. Follow the instructions precisely. Open the block drain on the R side whilst flushing.

Running hot on the highway is a sign of a radiator problem if the thermostat is working properly. Running hot at idle is a sign of an air flow problem e.g., fan clutch, air dams, clogged fins or the shroud.

A properly working thermostat controls the minimum operating temperature. A sticking improperly working thermostat can cause temp problems at speed. The rest of the cooling system controls the upper temps by shedding heat mainly through the radiator.

[87tdwagen]

A easy step that you can do is to give the radiator a good external cleaning. No mention if you have AC, but if you do, clean it and the void between it and the radiator. A good regressing, straighten out fins and see who you fair.

A good pre-test would be to aim a bright light, flashlight from the engine side out and see if the light comes thru all of the coolers. If not, you have some blockage and cleaning is in order. Simple to do and will rule in or out any airflow blockage issues.

[123mike]

Great help. Flush from heater hose was a new trick. It is very rusty and oily. The rubber hoses are coated with rust flakes. Gave it a super flush and ran Cascade for ten minutes . I don't have citris cleaner at the moment.

[Sugar Bear]

It will take repeatedly flushes to get it clean. Don't replace the radiator until it flushes clean. If it was mine I'd use CRC ThermoCure.

[123mike]

Check out the junk that came out radiator! I learned about the block plug a little too late. I'll do that next time. I was worried when the heater was taking so long to get hot, but it finally did. It only took about 1.5 gallons of AF, maybe the other 1.5 gallon in the block and heater core.

[123mike]

More info, I cobbled the 1980 300d hoses to the 1983 turbo engine that I installed. It's quite a mess but seems to work OK, I've been rolling in it like this at least 10 years. The heater fan only works in defrost. The second picture is how I turn on off water to heater core.