Spark plugs & temperature, 300E

[brabus3.6]

Hi!

I've got a 1989 M103 engined Brabus 3.6, with a couples of niggles that I imagine would be the same for all M103s. Firstly the spark plugs are fouled as shown in the picture after being cleaned and re-fitted 600 miles ago (there are new ones in there now). It looks to me like soot due to an overly rich mixture? The car is also hard to start when warm, requiring about 7 seconds of cranking and throttle depression. Once it's going it idles well and doesn't seem down on power whatsoever. It used to smoke on full kickdown but valve stem seals seem to have cured that.
Also a quick operating temperature question. When cruising the car will be around halfway between the second temp marking (60C?) and 80C. When ambient temp is under 10C the cruising temp will be just above the second marking. The car warms up to the 60C mark fairly quickly and I prefer seeing it below 80C than above, is this too cold or okay? I'm using Mobil 1 15W-50 in it which I assume is the best oil for the vehicle?

Thank you all.

[anthonyb]

80C is too cold. It should run right around 87-90C. Below 80, the cold start valve is open, enriching the mixture to get the engine temp up. I'd check/replace the thermostat and go from there.

[autozen]

I agree with thermostat first. With your operating temps the car is always supplying extra fuel by the EHA, because it thinks the engine is cold.

[brabus3.6]

I put a new thermostat in today, my old one was exactly the same part number but clearly opening too early. Now the car runs at, surprise, surprise... 87C, when the thermostat opens. I also adjusted the butterfly plate under the air cleaner which was catching. I loosened the 10mm and readjusted it so that it shut properly, starting is now within a couple of seconds with no throttle required. I pray it remains like that and is not just indicative of the new sparks not being fouled yet.

[A264172]

M103 3.6 that sounds like a neat engine.

Got any specs on it?

[brabus3.6]

Finally, car seems to be back to normal 1 year after the rebuild! Oh well, at least I'm there now .
Yes the Brabus sure is an exciting engine. I've got the exact specs at home which I will post when I get back. Of the top of my head I know it's 245BHP and I think 220lb/ft of torque. 0-60 is around 6 seconds and I've seen just over 150 to MPH out f it. It has a four speed autobox because it's a sedan but I know of one (and another that was written off! ) coupe with the 5-speed manual box. With that gearbox I'm sure the engine is good for at least 165, it really pulls hard. Mid-range is phenomenal.
The engine has been bored and stroked with lightened internals, forged pistons. The head (and inlet manifold I think) has been properly gas flowed, seeing it next to a standard M103 head you can see the difference. They also modified the camshaft and fitted manualually adjustable tapets. I'm sure with a free flow exhaust and forced induction kit at least 20BHP more can be alleviated but I doubt I'll bother and further strain the engine at 127000 miles.

Edit: them specs are correct. Brabus catalogue of the era mentions "a special crankshaft, forged pistons, modified inlet- and exhaust-passages and a Brabus camshaft", fails to mention the manually adjustable tappets. Compression ratio is increased as a result of the forged pistons from 9.2 to 10:1. Valves were also reprofiled. No other engine mods, though they added body kit etc. and an oil temperature measuring device so you know when you can really kick it

[autozen]

Brabus,
Congrats on getting the car squared away and thanks for at least listening to advice offered by some of the folks here who know something about these cars. You can't always be right diagnosing a car on the internet, but after 30 years of fixin on these things, you usually have a pretty good idea. I have no idea why some people ask questions on here, because they ignore the answers. Again congrats.