My 1993 240 runs great.... except when it's hot outside.

The most reliable scenario is a hot day (upper 80s+) the car will start up fine and run great, but then after running a few errands and the engine gets hot, the engine won't even crank. No noise at all.

If the car sits with the hood open for 15mins to an hour the car will start right back up again. Alternatively, the car will start right up with a jump, and can even be immediately turned off and restarted with no problems whatsoever.

Every now and then on a really hot day (100+) the car won't start even if the engine is cold and the car has been sitting unused for hours.

I've taken it to three mechanics and done my own admittedly amateur diagnosis without success. However the mechanics have not been able to reproduce the behavior while under their care.

At one mechanic's instruction, I hooked a test light up to the starter while it wouldn't start and it still lit up fine. He recommended replacing the starter, which I did, but the problem continues.

Could this be as simple a bad battery that hates the heat? Something else entirely? I've got a couple repair manuals, but far from an expert.

Thanks!

 

One piece of advice I can give is to STOP buying stuff right now. I'm not an expert either, but I sure have learned that little quirky things like these are not due to major part failure. If it starts with a jump or after sitting for some time, I would mess around with the fuses when It does not crank. The little fuse box is right near the door jam, left of your foot when sitting in the car if you don't know. Sometimes those fuses just don't work. Try that before you buy please, and see what happens.

 

Thanks for the response and your advice. I think you're absolutely right, having fought this problem for a good year or so and tried everything, a quirky fix makes sense.

 

So I just went fuse by fuse in the panel, removing them and testing to try to recreate the symptom without success. Any other ideas?

Thanks!

 

Kinda figured that wouldn't help. Well how old is the battery then. You said it does not work at first, but then when the hood is open, and that a jump would get her going. That really sound like it has nothing to do with the battery, but a short in the wiring maybe. A little loose connection, some adverse static electricity? Try and pop the negative cable off the battery and reconnect it, or just strike both cables with jumpers to get rid of a charge it might have.

 

carry around a cheap DVM. next time it won't start, read your battery voltage, read the voltage from the starter + lead to the ground. have someone turn the key and see if there's voltage on the solenoid control wire.

The control circuit goes from the battery to the ignition key to the transmission lockout switch (closed in P, N, and open in all other gears) to the solenoid control wire on the starter. The power circuit goes direct from the battery to the solenoid and grounds through the starter motor... if you have 12V on the big red wire at the starter (and would be pretty hard not to), I'd be looking at the control circuit, which is blue-yellow at the starter and purple at the ignition key.

there's also a service connector under the hood, it has two purple wires going to it, and you jump this together to fire the starter from under the hood (assuming the ignition is already switched on). if this works, and the key doesn't, I'd be looking at that transmission switch and/or the wiring to/from it, or the ignition key switch itself.

 

thanks, I'll give it a shot next time I can recreate the problem

 

Always start cheap and simple.
Starter safety switch on shifter, starter relay, battery cables (condition and connections), battery and battery terminals.
The battery, starter and ignition switch should be towards the bottom of the list.
A test light and a meter are handy to have around.
Ed

 

Your 240 has a single spade female terminal test port just to the right of center on the firewall. You can run a 12 or 14 ga. wire from it ot the starter. It's purpose is to bypass the neutral safety switch on the shifter. Leave the wire in place long enough to convince yourself that the situation has been eliminated. Then replace the switch. A word of caution...doing so will allow the car to start in any gear. I drove my 240 like that for a couple of months until weather improved enough to replace the switch. Assuming the battery is healthy and the alternator has great output under load, I'd start there.

 

I have an identical problem to this Forum user who titled her initial post as above. Mine is a 1993 240 Wagon, owned since new. It does not crank when hot. It has a manual transmission and I can "jump start" by getting it rolling and popping the clucth (NOT by using jumper cables). I have been chasing this problem for over four years and have spent almost $2,700 doing the following: replacing starter relay and fuse; replacing starter motor (which includes the attached solenoid); replacing in-line fuse holder and fuse; replacing the battery; replacing the alternator; replacing the ignition switch and the starter motor again (suspected a defective Bosch rebuilt one from prior replacement). This is largely a summer problem, when underhood heat builds up after a long drive. Turn the car off, and it will not crank. There is a vague click audible in the passenger compartment and dash lights dim as normal when the starter is engaged. Seems like a problem solenoid, but it is not. The only solution (other than to roll and jump start) is to open the hood and wait a half hour for the heat to dissipate. Then it starts. I love the car but am at wit's end. The problem cannot be an automatic transmission lock-out because it has a manual transmission (which does not require depressing clutch to activate starter). Any ideas woud be most appreciated.

 

thats 'bump starting' not jump starting

if the current drain is dimming the lights, then power is getting to the starter... I think at this point in time, I'd consider pulling the starter, and using an inspection mirror and ligth or whatever to view the gear teeth on the flywheel that the starter engages against... manually turn the crankshaft 15 degrees or so, repeat the inspection, til you've gone all the way around. my guess is, there's some spots on the flywheel where its seriously grungy.

that or the ground is bad at the starter. or the main battery cable from the battery to the starter is funky. or the battery ground.

 

battery taking a dump...

Air filter clogged
leaking injectors
CORRODED battery connections "ESPECIALLY GROUND"....clean the ground cable

 

When this happens, do you for example have lights and the horn is OK? If so then I suggest you to put the key in start position,put gear in neutral and then you pump the clutch pedal to get the starter on and see if it will help. There is some kind of a connection between the clutch pedal and switch. If it still wont start then can be the ignition switch or the ignition module. Also clean all fuses by taking them out,looking for any corrosion in each one of them and clean also the fuse terminal. Also when this no start happens I can also suggest you to put the car in gear 2,get out of the car and give the car a little hard push to get the startermotor teeth rolling so as to grip better. Then sit inside and start again and see if it helps. If this helps then you have a bad starter motor afterall.

 

240s have those awful ceramic fuses. the tin ones available in car stores from Buss or Littlefuse are junk, they oxidize and crumble. I suggest replacing ALL of them with the proper german brass or copper ceramic fuses. you can get those proper ceramic fuses from ebay by searching for 'mercedes fuse kit', enough for at least a whole car for cheap.
mercedes fuse kit | eBay

clean the fingers on the insides of fuse contacts with a soft pink pencil eraser too.

 

I was thinking about that vague click coming from the passenger side. What could that be and does it have a connection to the no start of the starter? Some relay or box that does not work alright and hence clicks?

 

click is from them fuel relay on the passenger foot rest...white or black...well at least on my 87 wagon. and would hear the click but there was nothing wrong with the relay...

I opened the relays plastic cover and the clicking sounds is when you turn on the ignition and two contacts make contact on each other kind of hard...click...

behind the carpet.

 

OK,then that is the way its supposed to be. That click is not connected to the no start she is having then.

 

right...I was curious of the clicking myself and popped the relay cover off and saw the connection between the ignition on and clicking...my no start was different...

I bought a new fuel pump relay and gave out in one week.....they get really hot...now I have my cover off...I suspect the new relay did not handle the heat well...the old one is still good...and gets hot really bad but handles it well...Original relay....the new one I bought is for emergencies only as it did not last long....COST 17 dollars but you can get one from FCPEuro.com for 12 bucks I think...to be sure...and have as these things go out...I actually have 5 of them hanging out..from my old Volvo's I sold.

 

I highly recommend getting Steible(sp?) aka real volvo relays, the aftermarket replacements re much funkier. the steibel(?) logo is a circle with an S in it that has like )( drawn through it.

 

Hello all!

Has anybody solved this with their own car? I’ve been having this issue for three years and yesterday was horrible. It didn’t cool off even with the hood up because it was so hot outside. I had it towed to my mechanic, but because it only happens when it’s hot and the weather isn't going to get that high again for the foreseeable future so I'm torn between leaving it and picking it up as is. I went to the mechanic's last night and of course it started because it had cooled over the six hours and sunset. I've tried everything mentioned that I've read so far here (well my mechanic has). I don’t know how they’re supposed to diagnose it unless they leave it running on an 80+ day for a half hour with the a/c on I’m not particularly car savvy myself but I love researching it and I'm looking for any previous solutions (if any have presented).
Thanks!!