I have a 1991 MB 300E. Just replaced head gasket after having the head machined and pressure tested. New water pump and thermostat. Radiator is 40K miles old. Car has 186K miles. Car is running hot.


Asked by Apr 18, 2012 at 11:46 AM about the 1991 Mercedes-Benz 300-Class 4 Dr 300E 2.6 Sedan

Question type: Maintenance & Repair

I would appreciate your input.

7 Answers


Is it running a little hot or in the red hot? Some things to check......... !. Check for trapped air in the cooling sysytem. To do this......Locate the thermostat housing that sits between the fan and engine and has a small hose going to the reservoir of the radiator. To bleed the cooling system you need to remove this hose, start the car and keep filling the reservoir until water comes out of the top of the thermostat housing. With the water jetting out reconnect and tighten this hose. NOTE: Be careful if your housing cover is made of plastic as the small outlet can break with too much pressure. This will probably do it. If not check these......... 2. Make sure thermostat is in properly. 3. Is the heater blowing hot air. a. If your not getting hot air through heater possible air. You will need to purge air out. 4. Stuck thermostat. b. take thermostat out and see if it runs cooler.

3 out of 3 people think this is helpful.

Aztec626bf --- thank you for your prompt reply. Today, we tried your suggestion. The thermostat housing is fine - there was coolant circulating. We bought a new radiator cap for the expansion tank. It seemed to have solved the overheating issue. On another note, we have noticed that the car is dripping oil. One quart of oil was gone in a matter of few minutes of test driving it. Other than a rear main seal, what could be the problem? Thank you so much!


Three options to where the oil is going, on the ground, out the exhaust or into the radiator. For the radiator look into the coolant reservoir and see if you notice any indication of oil. If its burning that much oil you would notice smoke coming from exhaust. You will also notice a heavy film in the tailpipe if your burning excessive amounts of oil. If your dripping that much oil you would see a fairly substantial puddle under car.


"Heavy" drip under the car when parked. There is also noticeable oil where the car was driven. I have not observed white smoke coming out of my tailpipe - only from the underside of the car. And since we just did the head gasket, no oil in the radiator expansion tank. Many thanks! Your help is very much appreciated.

1 out of 1 people think this is helpful.

It could be your head gasket or it could be something easier. if its leaking when shes just sitting your gonna have to just clean up the engine and wait to see a drip.


Thanks to Aztec and Blake. Finally able to pinpoint where the leak was coming. It turns out it was coming from the valve cover - a $7 fix using a silicone sealant. Car is running like it was brand new and just passed smog. I expect to get another 150K miles from this baby. I had it for 21 years now. THANKS AGAIN!

1 out of 1 people think this is helpful.

Goodmorning when you had the engine machined, and new head gascet replaced was this done under warranty, and at a reputible automotive shop, I would first take it back and have them do a full diagnosis to see why this is happening. I would guess it is probably a radiator problem, and havem also check that out. Thanks David Beckman

Your Answer

Add photo

Related Questions

  • Starting Problem 12 answers

    Starting Problem, 1991 300E Mercedes, Westborough, MA 1st flare-up – car initially starts and operates with no problem. 2 miles down the road, suddenly runs very rough sputters & bucks and stalls ou...

    1991 Mercedes-Benz 300-Class 4 Dr 300E Sedan


    Maintenance & Repair

  • 1990 300E -idles rough and stalls at stops 9 answers

    cold start is fine, after it warms up it idles rough and stalls at stops, sometimes it will restart most of time it wont start, I think the mixture is to rich for one. also noticed that when it does...

    1990 Mercedes-Benz 300-Class 4 Dr 300E Sedan


    Maintenance & Repair

  • repairing oil leak to coolant resulting in car running hot. 2 answers

    oil mixed with coolant and runs hot. have flushed it but it continues to run hot. i suspect a blockage. what are solutions

    Mercedes-Benz 300-Class


    Maintenance & Repair

  • starts cold but when hot hard start 1 answer

    1987 300E mbenz starts quick and runs without stalling but when stops and turn off engine it will not start like no gas but gas pressure is good, suspect electrical coz not conitinous spark from plu...

    1987 Mercedes-Benz 300-Class 300E Sedan


    Maintenance & Repair

  • Big car problem 4 answers

    Oil is in the radiator water. It has run "hot" once or twice...the last time while idling. I can't afford a new car. Would this one be worth fixing? It has 174,000 miles on it. Thanks. Susan

    Mercedes-Benz 190-Class


    Maintenance & Repair


Looking for a Used 300-Class in your area?

CarGurus has 180 nationwide 300-Class listings and the tools to find you a great deal.


Search Mercedes-Benz 300-Class Questions

Mercedes-Benz 300-Class Experts

#1 James Ramond
James Ramond
Reputation 240
#2 Tom Demyan
Tom Demyan
Reputation 210
Reputation 180
View All

Related Models For Sale

Used BMW 3 Series
981 Great Deals out of 31,676 listings starting at $1,000
Used Mercedes-Benz SL-Class
40 Great Deals out of 2,840 listings starting at $3,500
Used Mercedes-Benz G-Class
6 Great Deals out of 1,225 listings starting at $23,500
Used BMW 5 Series
491 Great Deals out of 15,930 listings starting at $1,700

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.