Does this sound like a failed thermostat, water pump, or other component? - PeachParts Mercedes-Benz Forum

1981_300sd · #1 12-23-2008, 02:25 PM

Hello,

During stop and go traffic for Christmas shopping, I noticed my car hit the red line. I tried to shut off the car when stopped to cool down, but I currently have vacuum issues im still working on, so it would not shut off for me. I could not get out and manually turn it off because I was in busy traffic.

It only hit the red line for maybe 30-60 seconds. And the car seems to be ok but I need to find out why this happened.

When driving on the freeway or basically over about 40 mph, the temp will stay correct. If driving slower, it will creep up to 100-110 degrees and then will fall back down to a good temp. If I am stop and go driving like in traffic, the temp will continue to rise until the car is shut off, or until it gets up to speed.

This really sounds like a water pump or thermostat issue to me, any ideas on what I should look on replacing first?

Thanks and happy holidays!

rrgrassi · #2 12-23-2008, 02:32 PM

Could be a failing t-stat, air flow over the radiator blockage, fan clutch, failing water pump, internal water flow blockage, or low coolant lavel.

kuhns34 · #3 12-23-2008, 03:23 PM

I just had a t-stat go bad in my 82 300 sd ran hot on the highway cooled off when i was driving under 50

rrgrassi · #4 12-23-2008, 04:34 PM

The t-stat is the least expensive, so start there.

t walgamuth · #5 12-23-2008, 05:07 PM

Low coolant is actually the least expensive!

Cr from Texas · #6 12-23-2008, 05:07 PM

Quote:

Originally Posted by rrgrassi

The t-stat is the least expensive, so start there.

Low coolant or blocked airflow is even cheaper to check and fix.

1981_300sd · #7 12-23-2008, 05:08 PM

Ya ill start with the tstat. The reason why I didnt mention other items is because this just started happening the other day, so I dont think its air flow over the radiator and so on. Ill check the fan clutch too. Thanks all.

carnut · #8 12-23-2008, 07:08 PM

And if the radiator cap is as old as the car, it is weak and will cause premature overheating as well.

sethgold · #9 12-24-2008, 01:05 AM

I don't have much diesel experience, but I've chased overheating problems on gassers so I'll take a shot.

First of all, are you sure it's really overheating? If it were me, I'd check the hoses and radiator with an IR thermometer just to rule out a bad gauge or sensor.

As others said, do the obvious easy things first: fan belt tension, coolant level, good t-stat and radiator cap.

If that all seem OK, I'd find a way to rig the fan clutch so it's always locked up. Use rope, wire, nuts & bolts, something to keep it engaged just long enough to test drive it. If your symptoms vanish I'd be pretty confident calling the fan clutch defective.

If the fan clutch is OK, consider the temperature of the upper and lower radiator hoses. Hot water enters through the top of the radiator and cooler water exists from the bottom. If the water temperature of the upper and lower radiator is close, then I'd suspect the water pump or radiator. In your case, you only see a temperature spike in stop and go driving. I'd drive it with the intent of making it run hot, then quickly check it. An IR thermometer would be ideal, but you might be able to get an idea by feeling it (carefully) with your hand.

If everything checks out, then I'd think your cooling system is OK. My next step would be to look for a pressure leak. If you don't own, or don't want to buy a cooling system pressure tester, a radiator shop should be to help you. Basically, it's a radiator cap with an integrated hand pump and pressure gauge. You run the engine with the radiator cap off until the engine is warm. Then you attach the tester and pump it until the cooling system reaches its normal operator pressure. Go have a beer or a latte. If the pressure dropped, look at your all your hoses and clamps for leaks.

I'm sure others will chime in with more suggestions. Just be methodical and you'll figure it out.