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AdamT 08-31-2007 05:58 PM

S320 running hot
My 94 S320 is trying to drive me crazier.

for the last few weeks, the car runs hot in stop-and-go driving. it's usual temp is right at 100deg, which i see from the forums is rather high.

when in stop and go driving for a bit, the car rises to 110, then past if it's really hot and i stay in town. when i get moving more it cools back down to 100.

the car seems to have no problem with interstate driving, remaining at 100deg.

the fan clutch seems fine (can't stop the fan running, or even slow it down), and the auxiliary fans are running.

if i turn the A/c off, the car runs less hot. it's around 100deg. outside every day, and the car minds night driving less (when it's around 80).

I see no sign of sludge on the oil cap, and no milkshake in the coolant bottle, so i'm hoping it's not a head gasket problem.

i'd appreciate any help you guys can offer to get this fixed.

juribe2 09-01-2007 12:01 PM

100-110C looks normall to me when driving in stop and go trafic or when under heavy load, but there are some things you could check:
  • Aux fans working in the wrong direction? They need blow air to the radiator and start on high speed at about 105C.
  • I thermostat in goog condition?
  • Expansion tank pressure cap with good seal?
  • Have you drained the coolant recently? There could be air traped in the system.
  • Coolant leaks?
  • Fan clutch, but you said it's good.
  • Radiator might be bad in the inside (cloged).
If you haven't yet, I would start by installing a new pressure cap and thermostat. Those are cheap and are very important.

If you have no mayo inside the coolant tank, you head and head gasket are ok.

I hope this helps.

AdamT 09-01-2007 04:48 PM

thanks for the advice. from what i've seen on forums, the usual temp for this car should be 80-90, and mine always stays at at least 100.

the aux fans seem to be working as they should; i haven't lost any coolant. i just brought home a new thermostat. none of the parts stores in town had anything lower temp than stock, so i just went with that. if it turns out to be the thermostat causing the warm running, i'll just order a cooler one later.

that said, i would love for some one to point me in the direction of instructions for installing the thermostat. i've never replaced one before and don't want to screw anything up.

i don't see any past threads with instructions, which i'm sure is because everyone but me knows how to do it. :wacky:

dukegrad98 09-01-2007 07:45 PM

Maybe your water pump is starting to head south? I've heard that some M-B water pumps use plastic impellers, and blades can break off -- but I don't know what models this may affect. Such a problem would result in less coolant flow and higher temperatures. I'm not sure how to check for that, but I bet someone here on the forum can tell you. If that's it, repair or replace before the whole thing goes and you warp a head or blow a gasket overheating! You're probably fine right up to 120, but keep a close eye on the needle. Good luck...

Cheers, John

juribe2 09-02-2007 10:21 PM

I don't know where the tstat is located in your car but in mine (M104) is where the upper radiator hose conects to the engine block. You just need to remove 3 bolts, replace the thermostat and o-ring and close it again. Pay atention to the thermostat position. It can be installed backwards.

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