Classic head gasket sign? 91 300e overheating - PeachParts Mercedes-Benz Forum

haasman · #1 08-07-2004, 11:50 PM

The 300E got hot today, very hot. The coolant temp went over 120 and briefly into the red. I checked the radiator and sections were cool while others hot. Ambient was about 89-91 degrees F.

I replaced the radiator late this afternoon expecting all to return to normal .... but .... the engine continues to get very hot and the coolant in the coolant reservior is bubbling/boiling. Engine temps are going above 120 with ambient now only 76 degrees F.

The aux fans do not come on by themselves. They will come on if I jump them at the receiver dryer bottle, but even then the engine continues to get too hot.

I have fresh non-green coolant and a relatively new T-stat.

Is this a classic indication of a bad head gasket? The coolant does not have any oil in it and I just passed an emissions test (Calif) today.

Haasman

EricSilver · #2 08-08-2004, 12:12 AM

Shouldn't there be steam in the exhaust as well?

Also, are you losing coolant too?

EricSilver · #3 08-08-2004, 12:22 AM

If You are not losing coolant and there is no steam in the exhaust, my money is on the water pump.

What popped into my head was belt slippage over the WP pulley; or perhaps bad impeller vanes; or maybe some disconnect between the pulley and the impeller.

I hope it is something simple.

brewtoo · #4 08-08-2004, 12:23 AM

Check for air in the system. Remove one of the plugs in top/front of head, the ones that plug the holes where a temp sensor could go. You can bleed any air out that way.

Also, check for a thermostat stuck closed.

haasman · #5 08-08-2004, 01:36 AM

Thanks for the replies .... I will check for a stuck T-stat. I have been loosing some coolant but not a lot. .... Maybe this is the telltale sign.

It seems that this problem has slowly been getting worse. The cold sections of the radiator seemed so obvious as to the radiator being the problem.

The engine also seems to heat up quickly ... maybe just the summer temps.

Haasman

Mike Murrell · #6 08-08-2004, 02:22 AM

Haasman:

Does this occurs while idling or while underway on the open road with plenty of air flow coming through?

haasman · #7 08-08-2004, 03:19 AM

Mike

Either: idling or moving down the road.

Does this say something to you?

Haasman

JoeR · #8 08-08-2004, 10:22 AM

If the overheating is happening while at steady speed on an open road, I would check:

1. Thermostat. Take it out and place in a pot of water on the stove with a thermometer. You should see it open at the proper temp. And hope it's that!!

2. Water pump. (expletives deleted)

John Plut · #9 08-08-2004, 10:39 AM

From your symptoms it sounds like you have major blockage that could be caused by a bad stat or collapsed hose. A bad head gasket would probably over-pressurize the cooling system before the engine has time to overheat. Check for oil in coolant and coolant in oil though.

I would definitely check the thermostat first. I had a Whaler stat actually break for no apparent reason. For testing, you can remove the stat completely. Of course the car should run cool and you should put a new stat in as soon as possible.

EricSilver · #10 08-08-2004, 10:57 AM

Two winters ago, during a major snowstorm, I had symptoms exactly like yours when my coolant froze in the lower radiator hose. I shot up to 120 just trying to get out of my parking space. It also got hot really quickly. (The top radiator hose was hot, but the lower hose was icy slush.)

Blockage now sounds more likely and I agree with the others on the stuck thermostat.

haasman · #11 08-15-2004, 01:23 AM

Follow up:

The 300E is now running properly and stays mid-point on the temp gauge. As it was suggested, the thermostat was stuck. I replaced it and never gets too hot.

Thanks for the suggestion. I had one tech trying to convince me that I needed to do the cylinder head.

Haasman

BenzRepair · #12 08-15-2004, 07:32 PM

Stat is cheap, and usually a good place to look when temps shoot up. I stick a cooler stat in my customers cars that run hot (~100C) even with a new stat; stat# for cooler (79C) stat is 110-200-06-15 (OE stat is 87C). Often this is all it takes for older, hotter running M102, 103, 104 engines to run within range.

Make sure stat is OE or made by Behr (has BTT stamped on housing somewhere); the aftermarket Wahler and other stats start to stick after about a year in my experience.

haasman · #13 08-15-2004, 10:18 PM

BenzRepair

Thanks for the post- I just had someone tell me the same thing. I opted for the standard 87C Tstat. The engine run at normal temps now.

Question: Wouldn't a cooler Tstat make the engine run too cool and promote early engine wear?

Haasman

BenzRepair · #14 08-15-2004, 11:59 PM

Quote:

Originally Posted by haasman

....Question: Wouldn't a cooler Tstat make the engine run too cool and promote early engine wear?

Haasman

You may have a point; let me re-phrase and say I only recommend sticking them in an older, higher-mileage vehicle as a potential fix for a common problem. It typically runs about where it needs to in these cars anyway, and are primarily for my customers too cheap to fix the actual cause of the overheating. However, better the cooler temps, than a warped head or greatly accelerated head gasket wear resulting from too much heat. It also makes a great summer stat if you experience higher temps than normal.

haasman · #15 09-21-2004, 03:15 AM

I found out the problem: I pulled over when the car was hot and had just been driven and very carefully reached in between the radiator fan blades and found sections of the radiator cool while other sections screaming hot: Blocked radiator!

I was a bit amazed by this since I have carefully used MBZ coolant. Must have been a bad core from sometime ago. One thing I did notice is that the overheating gradually increased.

I also replaced the Tstat with the one called for the car, I believe an 87C.

The car hasn't gotten too warm since across hot very hot days with the AC running.

Hot this helps someone trying to figure this out.

Haasman