M103/M104 ENGINES OVERHEATING - Head Gaskets? - PeachParts Mercedes-Benz Forum

BAD300 · #1 05-16-2010, 06:25 PM

Guys.

I'm looking @ a 90 model 300E with 24V engine done 230k's. Has had the infamous head gasket done 4 years ago due to overheating. New radiator. You name it! Well it's overheating again now :shock: RACV (break down service here) can find nothing wrong to casue this.

Need to understand why these 6 cylinder engines have common overheating problems? Why the head gaskets let go? I realise the causes etc. What I suspect is that this is the reason you see so many W124 300E's for sale ridiculously cheap?? I know they are 20 years old or so but they are being flogged off cheap on EBay ALL the time. I nhave noted many have had engine issues EVEN with maintenance services performed on time & the rest!

Is it to do with the head gasket material? Cause' there is bugger all other gaskets readily around. I know of a guy in Sweden whop make multi-layer ones out of SS. $250 Euro or US?

Can anyone thoroughly experienced in working with/owning these engines comment pls? I'm getting a little over bothering with these engines from what I have seen lately. Is there something sinister with these cars that cause them to shoot the head gaskets after 170 odd k's?

My mother's V6 MX6 has 305k's on it & drives like new. Original head/gaskets! Pissin' me off

Are the V8's any different? Gaskets better perhaps?

Cheers,
Tim

JohnM. · #2 05-16-2010, 07:49 PM

Headgaskets on these cars are vary rarely the cause of overheating. 9/10 times the failure on original head gaskets is between a coolant and oil passage. And its usually oil into coolant system contamination. But this doesn't cause overheating. Bad water pump, clogged radiator, bad thermostat, and the use of non-MB coolant over an extended period of time is more likely the culprit when it comes to overheating.

If they replaced the head gasket because it was overheating, and it's overheating again because of the HG. They most likely did it WRONG. The new head gaskets are already reinforced in the weak areas and should be good for the life of the engine after you do it once. The stock HG is also good for up to about ~300HP according to the turbo'd crowd.

You also still see many 300E's running around on the original head gasket. But they are one engine overheat (120C) away from needing replacement! A lot of the 300E's for sale with bad HG's also have new radiators

Because the original plastic necked radiator busted (usually on the highway) and the engine overheated. New radiator, and then there's an fancy new oil slick in the coolant overflow bottle!

Why you see so many cheap ones is because unfortunately they have hit the bottom of the depreciation curve, for now. It's getting very hard to find a nice one because people are just driving them into the ground and throwing away the keys. No need to maintain it, or check fluids or do anything to it. Because it's a "Benz" and they can take it. They can take it. But it sure does leave 'em all dried up and nasty...

BAD300 · #3 05-16-2010, 08:06 PM

Quote:

Originally Posted by JohnM.

Headgaskets on these cars are vary rarely the cause of overheating. 9/10 times the failure on original head gaskets is between a coolant and oil passage. And its usually oil into coolant system contamination. But this doesn't cause overheating. Bad water pump, clogged radiator, bad thermostat, and the use of non-MB coolant over an extended period of time is more likely the culprit when it comes to overheating.

If they replaced the head gasket because it was overheating, and it's overheating again because of the HG. They most likely did it WRONG. The new head gaskets are already reinforced in the weak areas and should be good for the life of the engine after you do it once. The stock HG is also good for up to about ~300HP according to the turbo'd crowd.

You also still see many 300E's running around on the original head gasket. But they are one engine overheat (120C) away from needing replacement! A lot of the 300E's for sale with bad HG's also have new radiators

Because the original plastic necked radiator busted (usually on the highway) and the engine overheated. New radiator, and then there's an fancy new oil slick in the coolant overflow bottle!

Why you see so many cheap ones is because unfortunately they have hit the bottom of the depreciation curve, for now. It's getting very hard to find a nice one because people are just driving them into the ground and throwing away the keys. No need to maintain it, or check fluids or do anything to it. Because it's a "Benz" and they can take it. They can take it. But it sure does leave 'em all dried up and nasty...

thanks JohnM!

I have gathered that these cars are on their 3rd/4th owner & servicing has dropped off. I was more so considering the cars that have been serviced. As you point out. Once the head is redone. Should be good to go again for couple of 100k's you would think.

Btw. I know Roman (pumpish) does make a SS multi-layer gasket but I can't maneuver around his Swedish Website. I will try & contact him every which way & see if I can get one made & then freighted here. Very expensive though & long wait all the same.

Bottom line is I don't want to build this engine of mine & have it fail due to weak links in the build. I'm considering putting a V8 in instead but it has to couple to the rebuilt ($2750 later) 300E 4 speed. This way I could run gas & have the power & be done with the project.

ps2cho · #4 05-16-2010, 08:32 PM

Which head gasket was used? A good quality manufacturer such as Reinz should have no issues.

BAD300 · #5 05-16-2010, 10:33 PM

Quote:

Originally Posted by ps2cho

Which head gasket was used? A good quality manufacturer such as Reinz should have no issues.

Can't answer that. The car in question is for sale. Just an option for me to get the engine. I was merely wanting to know general information on these engines as I need to decide what to do. Rebuild or not?

I wish there was a V8 that I could mount my 722.3 trans to & be done with it? Set the LPG up without the 6 cylinder/turbo rot to sort out. This way I would have the power without the potential for it all to go wrong?

tjts1 · #6 05-17-2010, 12:32 AM

Failed clutch fan and the ridiculously high 105c trigger point for the aux fans are the death of these motors. Most 15+ year old Mercedes are driving around with a failed clutch fan. Most owners don't know any better.

Bondavi · #7 05-17-2010, 01:16 AM

retrofit for the 105c aux fan trigger point to 95 avail?

JohnM. · #8 05-17-2010, 01:39 AM

Quote:

Originally Posted by tjts1

Failed clutch fan and the ridiculously high 105c trigger point for the aux fans are the death of these motors. Most 15+ year old Mercedes are driving around with a failed clutch fan. Most owners don't know any better.

105C is still well within safe operating temperature. Is the engine making peak HP at this temp? Probably not. But there is absolutely no damage being done.

If the car is running at 105C often, there are big problems somewhere. I can count on one hand the amount of times my aux fans have kicked on in the last year. Only time it's acceptable to see 105C is idling in traffic, and the fans will kick on and bring it back below 100C very quickly. The fan clutch locks at 90C. So the engine should be running at just a tick above 80 during 99% of driving conditions.

The 95C aux fan mod is for those who either have other cooling issues elsewhere, or don't trust the millions of dollars Mercedes puts into engineering.

Quote:

Originally Posted by Bondavi

retrofit for the 105c aux fan trigger point to 95 avail?

Consist of soldering in a resistor at the coolant temp switch on the cylinder head. If you do a search for "aux fan resistor" you will find some stuff.

Cal Learner · #9 05-17-2010, 10:05 AM

It does seem as though a 103 with a properly-operating and maintained coolant system does not overheat. If it routinely reaches 105, there's an underlying problem, probably in the coolant system, and not in the air flow system. Blaming the 105C sensor isn't the answer, although reducing that trigger point with a modified resistor might make sense if the vehicle is routinely used for towing. Otherwise, I would look elsewhere for the fix to an overheating problem.

OzC36 · #10 05-17-2010, 10:10 AM

Quote:

Failed clutch fan and the ridiculously high 105c trigger point for the aux fans are the death of these motors. Most 15+ year old Mercedes are driving around with a failed clutch fan. Most owners don't know any better.

BAD300 reread tjts1 quote above.

Your engine is liquid cooled. This means fluid absorbs heat fron the combustion area of the head and block and is pumped into an air-cooled radiator. The fluid is cooled by air passing over the radiator and is re-circulated back to the hot sections again.

If the engine is overheating, it means that:

1. The fluid is not being pumped.
2. The fluid is not being cooled.
3. There is insufficient fluid.

There is a fan clutch on the inner part of the radiator fan that ensures that the fan only engages when the temperature is hot. If it fails...

To test, run the car at highway speeds (100 km/h plus). If the engine runs cool...great! Then run the car at traffic speeds (30 km/h or less). If the engine overheats...then you might strongly suspect the fan clutch.

The fan clutch is cheap to buy.

tjts1 · #11 05-17-2010, 10:50 AM

Quote:

Originally Posted by Bondavi

retrofit for the 105c aux fan trigger point to 95 avail?

I changed mine from 105c to 90c with a 700ohm resistor in parallel but you can choose any temperature with different value resistor. 95c trigger point would require a ~766 ohm resistor. 750 ohm is an easy off the shelf solution. I also changed my thermostat from the stock 87c to 79c. Even without a clutch fan, the electric fans rarely trigger. I also added a backup switch in the dash if the temp sensor ever fails.

Quote:

Originally Posted by JohnM.

105C is still well within safe operating temperature. Is the engine making peak HP at this temp? Probably not. But there is absolutely no damage being done.

105c on a daily basis with a dead clutch fan is death to the headgasket.

Quote:

Originally Posted by JohnM.

The 95C aux fan mod is for those who either have other cooling issues elsewhere, or don't trust the millions of dollars Mercedes puts into engineering.

I don't think mercedes takes it as a personal offense every time somebody modifies their 20 year old car. The fact of the matter is even if you keep your cooling fans in tip top condition, after 100k+ miles the radiator gets loaded up with all sorts of road debris between the fins. The radiator needs to be removed and thoroughly cleaned both inside and out to bring it back to its original cooling capacity. In my case I also had to straighten out a few hundred fins damaged by the brilliant 'mercedes specialist' who worked on it previously.

Quote:

Originally Posted by JohnM.

Consist of soldering in a resistor at the coolant temp switch on the cylinder head. If you do a search for "aux fan resistor" you will find some stuff.

Its an NTC (negative temperature coefficient) temperature sensor, not a switch. Early cars (pre 87) have a temperature switch and adding a resistor to these won't work.
Keep in mind that using an 1100 ohm resistor as in the article ( http://pages.prodigy.net/jforgione/MB_CTS.html ) wont give the same results in our cars. The W140 uses the same temperature sensor but the fans trigger at 100c or 310 ohm. The M103/104 trigger at 105c or ~270ohm. You have to recalculate the resistor values for your specific target temperature.
http://www.sengpielaudio.com/calculator-paralresist.htm
The known data points for this sensor:
115c = 200 ohm
107c = 250 ohm
100c = 310 ohm
80c = 560 ohm

BAD300 · #12 05-20-2010, 06:28 PM

Quote:

Originally Posted by tjts1

I changed mine from 105c to 90c with a 700ohm resistor in parallel but you can choose any temperature with different value resistor. 95c trigger point would require a ~766 ohm resistor. 750 ohm is an easy off the shelf solution. I also changed my thermostat from the stock 87c to 79c. Even without a clutch fan, the electric fans rarely trigger. I also added a backup switch in the dash if the temp sensor ever fails.

105c on a daily basis with a dead clutch fan is death to the headgasket.

I don't think mercedes takes it as a personal offense every time somebody modifies their 20 year old car. The fact of the matter is even if you keep your cooling fans in tip top condition, after 100k+ miles the radiator gets loaded up with all sorts of road debris between the fins. The radiator needs to be removed and thoroughly cleaned both inside and out to bring it back to its original cooling capacity. In my case I also had to straighten out a few hundred fins damaged by the brilliant 'mercedes specialist' who worked on it previously.

Its an NTC (negative temperature coefficient) temperature sensor, not a switch. Early cars (pre 87) have a temperature switch and adding a resistor to these won't work.
Keep in mind that using an 1100 ohm resistor as in the article ( http://pages.prodigy.net/jforgione/MB_CTS.html ) wont give the same results in our cars. The W140 uses the same temperature sensor but the fans trigger at 100c or 310 ohm. The M103/104 trigger at 105c or ~270ohm. You have to recalculate the resistor values for your specific target temperature.
http://www.sengpielaudio.com/calculator-paralresist.htm
The known data points for this sensor:
115c = 200 ohm
107c = 250 ohm
100c = 310 ohm
80c = 560 ohm

Thanks tjts1

Thanks to all you guys for the info. This is why I appreciate & refer others in Aussie to this sight.

Whilst there are some members here on another site that are helpful & know a thing or two. The ratio of Merc owners here to you well......speaks for itself. I hate getting a bum-stear (the runaround) when I need facts to build this car right & know how to maintain it as I will be keeping it now for the inevitable future. Even if it is just as a daily driver up ahead someday.

Thanks again.

mak · #13 05-21-2010, 11:13 PM

The Bentley Publishers 'The 124 Bible' carries an detailed article on how to adjust the cut- in temperature of the fan clutch .and it works very well.

To bring down under hood temperature a Exhaust heat wrap on the manifold pipes works wonderfully.The engine and underhood stay much cooler .
mak
300se

macdrone · #14 05-22-2010, 01:27 AM

Use a 1.1K resistor inline eith the 2 prong engine temp sensor to turn the aux fans on 10-15 degrees cooler than usual. They will run more frequently but will keep you cool. I also suggest new reservoir cap if it doesnt hold pressure it will boil and overheat, also replace the thermostat, they go bad frequently. Water pump if you get the chance. I did all the replacement parts including the coolant reservoir only to find out it had a leak at the small neck to radiator and the cap held aalmost no pressure.

Good Luck.

samiam44 · #15 05-23-2010, 11:06 PM

Well, these cars did quite well new-

So something isn't up to snuff. My thought is you possibly have a cheap aftermarket water pump. The impeller is not pressed in to the correct depth and it isn't pumping like it should. I've had VW's where the impeller was plastic and had cracked. When the rpm got over 3-4k. It would slip.

Make sure the system is clean of oil, citric acid flush first. Test the fan clutch..

Michael