If the starter gets too hot, will it not engage?
 

The other day, I took a trip downtown (approx. 20 miles) to drop off some paperwork for my job. I had the stereo on loud (which has never made my car not start, even though it draws more than stock)

The car got up to about 100*C by the time I was there (which has been happening sparatically) Even on the hottest days sometimes it will never go past 90*C and just stick right between the two lines where it is supposed to be. Other days, it will ride at 100*C.

Anyway, when I parked, the temp. gauge read 100*C by this time the radio had been off for quite a while and I am sure that there was enough juice to restart the car.

After maybe 15 minutes I came back and the car would not start. The temp gauge still read just under 100*C. Glow light went, everything is normal until I bump the starter which makes the solenoid click, but the starter will not turn. I thought it could be the NSS but I dont think the solenoid would even click if that were the case. I put it in neutral just to see, and it still would not start.

I stopped and thought... I knew from previous endevours into electronics that the resistance of a wire (or any electric device ie. a starter) increases with temperature. This means that it takes more amperage to turn the engine over. I thought that was the reason it would not start. I opened the hood in a attempt to cool it off. After 10 minutes or so I tryed to start it again but all I heard was the click of the solenoid.

A man in a SUV drove by and I asked for a jump. He was willing and helped me jumpstart my car. This worked, turned over and started first time. What gives?

On my way home I stopped to return something at the store. When I was about to shut down the car, the temp gauge was showing 100*C again. I turned on the heat and kept the hood open and the engine idling until the temp gauge read 90*C (normal). I checked the voltage with a DMM and at idle it read 13.1VDC. I then shut the car down. I thought I should try to start it, and again this time it would not start.

I returned my item at the store and came back to the car, and it started right up.

I have not had any touble since this (but have only gone out on short trips) and my temp gauge has not been that high again yet.

Is it possible that the starter is just getting so hot it will not start without a jump?

this is a 1985 300SD with just over 200k miles. The starter is a Bosch rebuilt unit, the battery is less than 1 year old, and the voltage regulator has been replaced within the last year also. The alternator charges fine and this is the first time (since fixing my car) that it has not started. Also, I checked the grounding strap, and it is making good contact.

Any help is appreciated.

A couple of years ago my 300DT was doing the same thing... cool starts fine. Hot starts not happening. I figured it was my starter. I was planning a trip to L.A. and didnt want to get stuck on the road, but the car was acting normal.. it would even start on hot starts. My mechanic didnt think the problem was with the starter so he didnt touch it- and told me to drop back if it wouldnt start up again. But for some reason it was fine for the next few days.
So im on my way to L.A., stop for gas about 3 quarters of the way there. I was hesitant to turn the car off incase it would decide to not start... but I had to in order to fuel. So I did. And of course it wouldnt start after. I was with some friends so we rolled the car into a shady parking spot and popped the hood. After doing some crossword puzzels and reading, the car had cooled down considerably. BUT it wouldnt start. SO i had a friend jump in the driver seat and turn the ignition key, while i got under the car and started hitting the starter with my lug wrench. Sure enough it started right up! As soon as we got to our destination in Huntington beach, I dropped the car off at a shop in Costa Mesa and had them replace my starter. Its been fine since.

There a many things that can keep a car from starting, but id suspect that it might be your starter. A friend of mine had her starter replaced in her 300SD before embarking on a trip to Oregon. However, the replacement starter wasn any better than the old one.. and the replacement unit was a Bosch unit. SO when she got back to CA, she took it back to the shop that replaced it- an MB indie, whom promptly told her that it was probably a faulty unit from Bosch. They replaced it at no charge this time.

Im not sure if this is your prob, but in my only experience with my w123 failing to start, it was the starter.

Replace the battery or clean all the cables.......or both.

The fact that you can jump start the vehicle with another battery rules the starter out.

I was having the same problem with my car, only clicking when hot but fine when cool. It would also start 75% of the time with a jump. I tried for a month to fix everything but the starter but I finally had to break down and replace it. I think the extra voltage/amperage from a running vehicle helps the solaniod engage. The starter would turn just fine, the solanoid just wouldn't kick in without the extra kick from another vehicle.

If the voltage is increased from a running vehicle, it's possible that the 13.5V will allow the starter to turn when 12V will not.

But, my bet is still on a battery, or cables, that allow the cranking voltage to drop well below 12V when the key is turned.

Sady,

Its true that resistance increases with an increase in temperature. So a hot starter will have an overall higher resistance and draw less current with a reduction of output torque and power. I have seen starters that would start a cold engine but not a hot engine. This type of bad starter, when hot, will draw more current with a decrease in output torque and power.

So if your starter cranks the engine well when hot, the armature and field coils are OK. It may be a resistance on the surface of the contacts points in the relay of the solonoid or the brushes in the starter are worn or have weak springs and are not making good contact. The extra voltage from jumping to another vehicle may be just enough to get enough current thru the higher resistance and get the starter going after which it works OK.

Sorry, I can't explain why it only happens when hot.

P E H

Im going to be out of town a coulple of days for memorial day, but when I get back I can run more tests.

It is just so odd to me that this would start now, because the engine has been this hot before. I guess it is just because it is so hot outside?

Ill clean my cables (again) when I get back and see if that does it for me.

I would really like my car to be reliable in any weather conditions.

Could it really be the battery if I just replaced it less than a year ago?

Is there anything else that I can test before spending money?

What is it that I should do?

I would say if it started with a jump but not on its own/with your battery, then its probably toast. I'd look to the cables or battery, they are probably the only thing that could be a problem. Batteries can go bad at random, even if only a year old, what kind is it?

Are you sure the clicking is coming from the solanoid? Now that I think about it, I'm mistaken in what I was remembering when I posted earlier. I heard what I thought was the solanoid clicking but I think it was really something under the dash, maybe the lockout that only lets you turn the key to "start" once. Thinking about it, I got under the car once when it was acting up and the solanoid didn't make any sound at all. Right after I bought a new battery at Autozone, it wouldn't start. I went back inside and asked the sales guy and he said that he would see this problem alot when the weather would start to turn warm. He said the cause was the solanoid expanding and not being able to move. A new rebuilt Bosch starter saved the day.

Sady,

I doubt that its the battery. Once a battery goes bad, it rarly revives.

If U can duplicate the problem, put a voltmeter probe on the output terminal of the solonoid. U should read 12 volts. This will tell U if the solonoid or the starter is the problem. Since the current from the pick coil in the solonoid goes thru the starter to make the solonoid pick (click), the problem is probably in the solonoid. If U get 12 volts at the input to the starter and the starter doesn't run, then starter is bad, but probably only the brushes or the comutator needs to be cleaned.

Also test the voltage at the input terminal to the solonoid. Test at the stud and the cable. Both should be the same, 12 volts. If there is a difference, the connection there is bad.

P E H

electrical system weaknesses are always discovered in very high or very low conditions. you gave your system the heat soak treatment test and it failed. all of the things mentioned are possibilities.
i have been stranded when on trips many times in hot weather. so one of the benefits of driving a diesel is that there are no fumes to catch fire at the gas station. when fueling on a trip in hot weather i never shut the car off. ditto on potty stops. when going in for a meal i do shut the car or truck off but i always crack the hood open and leave it halfway open to let out the heat. i figure the wires and hoses can only take so much heat and eventually they will fail, so why give them any more than i have to.

just the observations of a long time traveler.

of course you can do all this and still get stranded, but when it is 100 degrees out why push it? around here it doesnt get that hot very often so if my system is only 97% good why fix it for three or four days a year?

tom w

It could, but the the chances are certainly diminished.

Check the voltage at the solenoid during cranking. It won't be 12V due to the load, however, it should not drop below 11.5V or so if the battery and cables are in good shape.

You can also have the battery load tested for free to double check it's output capabilities.

If the battery checks out OK, then, it's one of those intermittent situations with the solenoid. You'll have to change it or the starter.

Be sure to double check all cable connections, including the ground strap.

Well, Ill try not to get her so hot again.. I will (when I get back into town) go to autozoo and the battery tested.

I had been planning to upgrade the alternator this summer anyway along with most of the associated wiring. I will be adding grounding straps and with a bigger alternator, I hope I wont have a problem anymore.

If my battery was dead, would it start anytime when not so hot (like it does now?)

I still have my old starter (the bosch rebuild was a very nice gift from the owner of european autoparts) and I think the only thing wrong with it is the solenoid... would it be a good idea to get a new solenoid and replace it on one of the two good starters I have?

Would it be benificial to try to block heat from the starter somehow? an extra heat shield maybe? or what about those aluminum/fiberglass covers they have would that help?

I've had two batteries that AZ said were good but, when
 

I replaced them, my symptoms went away....:1blank:

their battery?

sometimes a second opinion is warrented.

tom w