86 300SDL Overheating Randomly
 

I gave the car to my dad to bring to florida for a few months to use as a car down there while i foxed up their florida car they never use. After he made the 1300 mile trip down there with it he told me it was overheating. HE put some antifreeze in it after he said it was low, (he's 70 and not always right) ;). My friend lives in the area and checked it out a month ago and it was hitting the 120 mark a few minutes after they started it. I finally made my way down here this week and cranked it up. I let it run for ten minutes and it ran fine, i drove it for about 20 minutes on the highway and side streets and it was 86 degrees out, I had the heat and AC on and the temp gauge was moving up and down but not above the 80C mark.

Any idea what this might be? I would love to bring it back to NYC to let me mechanic work on it but I'm scared of it heating up on the drive. I don't want to junk it as I've put too much money in it to get it running right the past two years.
We have owned it for about 5 years and it has 202k on it!

The water pump and coolant got changed about a 15 months ago as well but it wasn't by my mercedes mechanic since i didn't find him at that point yet.

If it overheats at a standstill, but not at speed it's a fan problem. Overheating while standing and moving is a water pump or thermostat problem.

(he's 70 and not always right)

Great something to look forward to I guess!

Thermostat first. Has to be eliminated. Also when heating check for a collapsed lower hose. Or if it is currently really soft. Basically rotted but not leaking.

I am not aware if a sticking fan thermostat is not another possibility.

Interesting double negative statement. Do you mean "I am aware if a sticking fan thermostat is another possibility" ??

On a serious note. This is what I would do if you want to drive it back to NY, provided the head gasket is sound. Wire up the aux fan to be on at high speed all the way. This can be easily done. Look for the 3 prong thermostat on top of the engine coolant tube to the radiator. Remove the 2 prong plug and jump them together. The aux fan would come on. Been there and done that when car in trouble. Good luck.

If it's really an intermittent problem, it could be a slipping serpentine belt. Do you have AAA?

Kind of a hijack, but I did what you describe last summer and it killed my fan. At the time I thought it was because I left the fan on at highways speeds, which I assumed was my stupid mistake...thoughts?

What was ambient air temp when your friend got it to hit 120 ?

If the engine was cold during the few min test, I doubt that the 120 was real given diesels tend to run cold at idle. I'd look at the temp gauge / sender and wiring.

I've had the bridge break on thermostats and the main valve stick open and the bypass disc open as well. This results in an engine that runs hot at idle and cold at speed.

See my post 5
http://www.peachparts.com/shopforum/tech-help/360009-1995-e320-running-hot.html

For the cost Id be looking at replacing the thermostat again or at least pull it and do a stove top check to see what temp its actually opening at.

Lots of good advice here but a 603 with goofy temp readings could be a cracked head or tired head gasket raising cooling pressure. Loss of coolant is one indicator. Is there residual pressure in the cooling system overnight? Do temp gauge fluctuations disappear or lessen if you leave the pressure cap on the first notch; that is, no cap pressure on the cooling system?

Sixto
83 300SD

I would say your aux fan was on its last leg. Leaving it on killed it. btw: I am just suggesting a way to get the OP back to NY. The overheating could be a combination of reasons.

Jumping the Fan
 

FWIW Ah-Kay is correct. I jumped my fan years ago for summer months here in the South West. A Mercedes technician from the '80s advised to do so. He said:

• Keeps the motor cooler in desert summer heat
• Helps the AC out

I used to worry about burning the fan out but now after several hundred thousand miles with hours on end running 75-80 mph across the AZ & NV deserts....no problems, and it definitely helps keep the motor cooler.

Fan Clutch
 

Could be a faltering fan clutch...I'd also double check the temp gauge system with an infrared meter. Just the same I'd also take a hard look at Sixto's advice.

Thanks for the reply gents. I've heard it said that the 603 aux fan is inadequate but I thought it worked pretty well. Well enough that I was fine without the mechanical fan; but the weather here is moderate in terms of heat. Plus I rarely hit stop and go traffic. Anyway hope I can get it fixed, seems like there is just one electrical component to wear out. Looks like a big resistor but it's probably a capacitor or something else. I've seen similar fans at the yard, maybe interchangeable. Well that's enough of a sidetrack. Cheers!

Several possible issues.
I'd check the belt spring and tensioner first.

Next would be the coolant. Make sure he didn't put green in there.

Pressure test the system...