Bit new to Mercedes but not new to wrenching. Have an 89 300SE with the M103 engine. I am trying to get my service manuals together but since MBUSA no longer sells the W126 Service CD's I am searching for alternatives. The car did come with the M103 engine manual and the W126 HVAC service manual though. I need the body manual so I can do brakes soon.

I cannot find in the M103 service manual what the proper plug gap is. I just returned from the dealer with 6 Bosch Non Resistor plugs (the box is even marked H9DCO) and they look to be pre-gapped to .8 MM on the box. Is that the correct gap?

Oil - the Previous Owner was running Castrol 10w40 in it. It has 147K on the clock and new valve seals, head gasket and lifters. I have to fix a leak on the upper timing case but other than that no bad leaks. Is 10w40 ok to use in the hot summers here? Temps are in the upper 80's to high 90's during the summer. I was thinking of a partial synthetic oil like Mobil 1 Drive Clean.

I have the gaskets coming for the Timing case leak and at that time I am putting in all new Plugs, Bosch wires, Bosch cap and rotor. The Cam seal as well as the valve cover gasket will be new.

Thanks in advance for the info!

The upper timing cover seal is a pain, not because it is hard to do because it isn't that hard, but you will have to do every two years if you're lucky. You definitely want to use the MB sealant, nothing else lasts even that long.

The oil weight is fine, but you may wish to research the whole zinc additive situation. If I remember correctly, they changed the cam metallurgy in '90 to eliminate the need for zinc additive, but the '89 may still have the softer metal cam lobes and require some type of zinc additive. I'm no expert on this, so ask around and search the forum. This topic has come up many times. My 300SE is a '90 and I run either Castrol Syntec or Mobil1 10W-40 depending on which is on sale both with good results.

Those plugs should be pre-gapped. I think the spec is .026" but that is PURELY from memory and not to be trusted without verification.

__________________
-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition

Nope, .036". See how memory fades as age increases?

__________________
-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition

.8mm or .032" is correct. I would check the gap before installing.
Gilly

__________________
Click here to see the items I have up for auction at EBay

Click here to see a photo album of my '62 Sprite Project Moneypit (Now Sold)

the proper Bosch plug will be pre-gapped at the factory....

Yup... Best to verify gap... That way you know it's right...

I will verify the plug gap for sure. Just wanted to make sure!

Funny I had searched out the proper plugs and not to use resistors before i posted the message. I had not even looked for oil. Thanks for the input.

I started to look into the oil doing searches on the board. Wow lots of different choices. not sure which way I will go yet.

Thanks again.

Recommend running Mobil 1 15W50 in your 1989 300SE. Factory fill for that vintage engine was 15W40 mineral oil. I run Mobil 1 15W50 in our MB automobiles of that vintage without any leakage problems.

I second the recommendation to use MB black sealant when resealing the upper timing chain cover.

__________________
Fred Hoelzle