bas_500sl, check the condition of the distributor caps, distributor rotors and spark plug wires. If those are in bad shape the engine will run poorly. Bosch replacements would be a good idea ... don't try to save a few bucks on those items. Apply a thin film of dielectric grease on the spark plug wire boots to make future removal easier. Look in the Owner's Manual for the proper spark plugs for your engine ... platinum or newer style spark plugs are a no-no for that vintage engine ... verify the gap is correct, even on brand new spark plugs.

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Fred Hoelzle

I had issues starting the car cold also (and hot) and what made the biggest difference for me was cleaning up the warm up regulator valve.

I did all of the other suggestions - check for vacuum leaks, tune up, cold start valve, etc. They all had to be done and all showed a little improvement, but the big one was the warm up regulator.

Hope this helps,

Dwayne

junker68
I have a issue with my 1990 500SL no way to start when engine temp. is at 75 Celsius .
Will start nice when cold or hod ,where is that warm up regulator located please?
Peter K

Thanks all for the responses. The overheating issue has gotten worse since the temps here in Tucson are getting hot 95 plus in tucson. I will have to spend some money on a new Radiator. Pretty sure that's the original one so is good to replace. Yes The car runs like crap when it is hot outside. I will look into the fuel issue and replace the caps and rotors. Is Autohauz az the cheapest for these parts?

Recommend a Behr radiator. Shop around for the best price. Best to replace the thermostat while you're at it. Use a 50/50 mix of distilled water and MB coolant. PH should be 7.

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Fred Hoelzle

Ok I found a replacement radiator on ebay. Its all aluminum for $209 shipped. I contacted seller to see if it was direct replacement havent heard back yet.

All Aluminum Radiator 90 93 Mercedes Benz 500SL V8 5 0L 8CYL Lifetime Warranty | eBay

Also I heard you can buy the coolant at NAPA?

I ordered the aluminum radiator from ebay. It was a direct fit. Installed it did a 50/50 coolant and distilled water. And now it does not overheat anymore. The old radiator was clogged had a lot of crud in it. Still looking into the running rich issue. But I am glad the overheat issue was resolved since its been 112 degrees here.
So I need to repair the running rich issue
The a/c cuts in and out? It was converted to new system. a/c condenser fans come on but shut off when its hot outside?
Thanks everyone for your technical knowledge. You guys rock!