m103

[pilot53]

Im thinking of buying a 300se with the m103 engine, i know they are known for headgasket leaks due to the use of dissimilar metals. Is there any way to permanently fix this issue, or is it just something that will need to be done over again?

[lorainfurniture]

It's like a once every 150,000 mile thing. Not really a big deal.

[gwg]

My tech told me that they improved the materials so it should be fine for a lot longer now. The key seems to be avoiding any overheating of the engine. If anyone knows any good ways to improve the cooling system I'd be very interested.

[97 SL320]

I don't think this engine is any worse that any other aluminum headed / iron block engine out there.

The M104 ( the 24 valve version of the M103 ) develops oil leaks at the front of head but that isn't a big issue.

The key for a lasting head gasket replacement is to fix any overheating problems like a bad thermostat , fins broken off the water pump , clogged radiator and more. And, make sure the head is flat and not grooved. An eroded head surface won't properly compress the gasket and it will fail later.

[benfield4]

I did the Head Gasket on mine as it was leaking oil from the back of the head onto the exhaust. I pulled the head and took it to a cylinder head shop where they went through it replacing 3 exhaust valves, guides and the guide seals. They also made sure it was square on the mating surface. Put it back on with the ElringKlinger head gasket set and new head bolts. It ran much better after that and oil consumption went down. I agree with the not letting it overheat advice. Mine used to swing in temp pretty bad on a hot day with the clutch fan. I was unlucky enough to by a Behr replacement clutch and it would spend the whole drive locked up. My car sounded like an airplane. Instead of blowing more money on the Sachs clutch I converted it to a SPAL electric fan and a larger alternator. Over the 3 years that I ran this combo it worked pretty well! On a hot day in traffic with only the spal fan on the temp would very slowly climb up to 92C then the aux fans would kick on and the temp would go down to around 82C. It would swing like that much faster when I had the fan clutches on it. You could feel that Spal fan kick on when the alternator would compensate with a blip in the idle. Other than that the 300SE is nice and has adequate power. It was always dogged down a bit taking off from a stop on a hot summer day with the AC and Spal Fan going. Sometimes popping down to first on a hill or when I asked for more power. I got a steady 20-21 MPG on my mixed freeway city street commute to work with the car. Even with it turning over 3200 RPM on the freeway!

[Ivanerrol]

Make sure you use the proper MB approved coolant and that your cooling system is up to scratch. This greatly reduces the headgasket problem.

[Hit Man X]

I put a Reinz gasket on my 300SEL around 270k... it leaks again at 310k area out of the same damned oil pressure port on the passenger rear of the block. I am not a happy camper, so I will probably be using Elring or OEM next time. At least I had the cylinder head fully rebuilt when it was off last time (12 guides, 12 valve springs, new stem seals, the works)



Be aware of the other quirks with the M103 in the W126 -

1. High RPM cruise (3400rpm @ 70mph) speed wears out the accessories faster, this includes the ignition system bits as well as the belt drive system
2. Only Sachs fan clutches work (well, in the aftermarket)
3. Gearing is very awkward and the 1-2 upshift is usually very harsh, so the Superior Trans shift kit is highly desired to cure this
4. Difficult to keep the motor from leaking oil
5. Only OEM belt tensioners are worth a damn

Aside from that stuff, it is a very durable and simple combination. Too bad MB never put in a larger displacement I6 in these cars like BMW did in this time frame.