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Q: Trouble Starting In Hot Weather on 1995 Mercedes-Benz C220

Just recently, as the temperatures have risen here in Florida my car is having trouble starting. If the car sits all day in a parking lot and the internal temperature of the car indicates 100 plus degrees the car won't start. If we wait until the sun goes down and the car cools we have no trouble whatsoever. Just today, car started at 8:15 AM just fine, ran two errands (stopped and started) at third errand the car wouldn't start. It was parked in shade, I waited fifteen minutes and the car started. I drove a couple of miles to my next destination, (around 11 AM) stopped car and tried to restart about 10 minutes later. The car wouldn't start. Tried again at 3pm, the car was VERY hot and wouldn't start. Going back tonight around 8pm and I expect to not have any trouble. This has just started in the last couple of weeks. Any suggestions would be appreciated. Oh and btw, the car has 219K miles....
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This seems to be the same problem I am having. Mine will not start over 83 degrees though. It has to be something inside the interior and not under the hood though as it starts just fine after running for hours as long as the internal temp stays under 83 degrees. This leads me to think it is something within the ignition and not the starter relay.

Does anyone have any ideas?
I have a 1996 C220 with approx 160K miles here in Houston Tx, in August and it seems to have the same problem which only started in the last few weeks. Actually, I don't drive this car much and it may sit motionless for three weeks at a time. I added premium fuel in February and started having this trouble on the same tank of fuel in August. I am suspicious of the fuel deterioration. So I added half a tank of fuel the other day to top it off (medium grad, thought I'd save a couple pennies) and today the problem was worse than ever. The interior temp was reading 90F, but I think it was hotter than that.

I cranked and cranked at various times today to try to get it started -- no luck. The owner's manual says do not press accelerator pedla while starting if cold and only press the pedal slowly when warm and having trouble getting started. I tried many permutations of this. I sometimes would crank the starter for maybe 20 seconds at a time, which is way too long I know, but that worked in recent times; not today.

Finally, this evening, I rolled the car out of the garage into the still-hot driveway. At 10PM its still nearly 90F outside. It sat out there for 5-10 minutes and, after cranking for 15 seconds, it started right up and ran like a top as I buzzed around the neighborhood.

[BTW, I kept a battery charger cpnnected while doing a lot of this since it was no doubt really hard on the battery]

My theory for why it started in the end was not becuase the interior temp had cooled to 88F, but becuase I shook the car around whien moving it out of the garage. I think sloshing the fuel had some effect since it was still about the same temperature as before when I couldn't get it started.

One other item... in the past I have had trouble with this fuel cap on this car -- it doesn't breath properly, I don't think. That is, when I would have trouble starting the car, I would simply go loosen the fuel cap and, voila!, it would start up. The act of loosening the cap would cause a gas-rush sound -- I presume it was under pressure and not a vacuum, but can't say for sure. That worked for me last week when this problem surfaced, but not in the last few days when I have had this starting problem.

Ok, one other tidbit... a year or two ago when I first got the car, I was driving it daily about 20 miles at high speeds (80-90 mph each day). If the afternoons when I went to leave the office, it would be 100F or more in the car, and it would start up without hesitation. I usually would get premium fuel back then, but sometimes would save the pennies and get medium grade. All the fuels have ethanol in them. (Now that I think of it, that friggen ethanol is probably the source of a lot of these problems)


Not long after I wrote this, the problem got much worse and the car wouldn't start at all. I ended up having to get the "fuel pump relay" replaced. It was pretty inexpensive to have done, in my case.

Update #2
A year later and my car got into the "won't start in hot weather" mode again, except this time it actually died on me when I slowed down to turn at an intersection and had to be towed to a shop.

The problem turned out to be the "crank shaft position sensor" and now it runs very well (perhaps better than I have ever had it run in the three years I have owned it). The part was $157 and labor (plus diagnostic) was about $285 -- not cheap for what it was, but it sure beats buying a replacement car.
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