Long time answerer (is that a word?) of questions, so I figure I am due.
I have a 1987 Ford E-150 with 160K - used to haul the racecar. It’s had a lot of issues and the latest is that when the engine has warmed up, then shut down, the starter struggles to turn the engine over until the engine cools Once it does, it turns over and starts right up.
I figure it’s the starter getting hot, but I want to know why this would be the case. Does the heat expand the starter shaft so it binds a bit with the bearing? Is it the increased resistance of the wire?
This is an interesting topic. I believe it has to do with more resistance in things like the brushes and maybe a break-down of the solenoid windings when hot. This would be assuming the E series has moved the solenoid to the starter like the little Ranger trucks but it may be located near the battery instead. I’m not well hearst on this vehicle. Anyway, I have always wondered the effects of heat on inductors but haven’t found good answers. If the inductance is changing you don’t get as much reaction from the current running though it. But again I believe it is more the brushes gaining resistance since most starter rebuilds have new brushes but not the core style windings.
I will be interested in others answers on this topic.
If it is the starter (that’d be my guess, too) it has to be something that’s changed/worn over the years, since this wasn’t happening before. If the starter shaft expanding was a problem, it would always have been a problem, same for wire resistance. My guess: somewhere there are contacts (solenoid or brushes) that have worn or gotten pitted to the point that heat causes a poor connection.
Motor windings are a relatively thin wire usually insulated with a varnish-like polyimid-amide coating. The coating has a very different coefficient of thermal expansion than the copper beneath it. As the coil wire expands and contracts with heating and cooling over time, the insulation eventuallly cracks from fateigue. Then, when the coils again heat, some of the cracked areas will open and short out windings, reducing the power in the motor. 1000 windings effectively become 700 windings, reducing the feild strength. When the motor again cools, the cracks close and the motor regains full strength.
This type of fateigue related heat sensitivity failure is common to anything with a coil, including motors, transformers, and relays. If it’s inductive, it’s susceptable.
The starter is probably heat soaking. When this happens a combination of things occur. The heat causes the components in the starter to expand. This can be exasperated if the components within the starter are worn out. The heat also effects the windings in the starter by increasing the resistance of the windings. So it requires more current to operate the starter. So the combination of the worn starter along with the higher resistance thru the windings causes the starter to turn slowly until the starter cools back down.
If you look at the location of the starter you’ll see that the right exhaust manifold/pipe run right next to the starter. And this is probably the heat source.
Did you ever notice that heat soaked, worn out starters that have this problem can often be started by banging on them with a hammer while attempting to start? The bushings wear out allowing the armature to drag when under intense electrical field drawing it off to one side and sometimes even rubbing. The heat has also expanded things which can worsen mechanical interference and reduce the electrical efficiency. All bad things for starter operation. Banging on it momentarily jars the armature back away from the interference toward the center and it gains momentum and spins albiet slower than a good starter would.
I had a big block chevy truck that did the same thing. Replaced the starter still did it, tried some other things, still did it. Found a old Chevy guy who said from the factory there was a sheet metal heat shield above the solenoid. Mine had rusted off and disappeared, he made up a new one and I never had the issue again.
I had this problem on my Chevy pickup truck with the 350 engine years ago. The heat shield helped but the final fix was a “heavy duty” starter. It cost a little more than the OEM starter but the slow or no starts were history.
I’ve got a 351 Ford Windsor motor in an old '87 ski boat (PCM) and had the exact symptoms. At first I figure when the motor was warm and I went to restart it (something you do often pulling skiers) that there was carbon built up and that caused higher compression. The 1st one of 2 revolutions of the starter would be real slow, and then it would get up enough speed to fire up the motor.
Eventually the starter failed and I ordered a new one from a marine supplier that was supposedly “stronger” then the one that failed. In fact, the new starter cranked the motor nicely, with no more of the slow cranking problem. I’d get a new starter.
I guess the question is why the starter is “tired” and has difficulty cranking the warm motor. I do think a warm motor has more compression, especially an old warm motor. The warmth helps the rings seal better, etc.
Electric motors don’t care much for heat, and a starter isn’t made to run constantly therefore it assumes the motor really won’t get that hot. Over time heat will deteriorate the coatings on the windings and essentially that means windings will short out against each other. The result is the same as a motor with fewer windings, that means a less powerful motor. There could also be more internal friction in the motor from worn bearings where the “lifetime” lubrication has outlived its lifetime. The brushes and springs wear out making for less effective contact with the armature. A rebuilder takes care of just such things when they take the core and turn it into a like new starter for sale at the auto parts store.
I once made a long cross country trip in my MGA. It exhibited the same symptoms as your van. If I stopped for a meal or fuel, I’d get a big cup of ice water and pour it over the starter to cool it. Overnights were not an issue as the starter was not heat soaked. It worked every time.
The question of “why” is always of interest. I’m guessing that there’s truth to all the theories. My own about the breakdown of the insulation is from having done failure analysis on transformers and other inductive devices after they’d failed thermal cycling in temperatures very similar to what a starter motor is exposed to. I’m certain that all the other theories are based in truth as well. I seriously doubt if there’s only one cause that fits all.
I like to watch these posts but not get too involved. what causes this problem on one vehicle may not be the same root cause on another. Just one thing I want to mention is do not compare a Dc motor with any kind of ac inductor, like a transformer. If two turns on a transformer arc, then the transformer is going to experience catastrophic and sudden failure, in other words, the smoke gets out, and transformers do not work when they lose their smoke.
DC devices do not have the changing magnetic fields that can generate either very high voltages or very high currents, depending on the turns that arc together. In most cases it is high current and immediately melts the wires. I have seen the results of this many times.
Ah, the old “heat riser” nick!
There’s more than one failure mode with windings. In my experience those that fail from repeated thermal cycling do so due to winding insulation fatigue failure. Burn spots will usually originate as either arcs or an unintended restriction in wire diameter (such as a physical nick)that causes a hot spot.
We won’t get to anlyze the motor, so the actual root cause will remain theoretical, but I feel pretty compfortable that the problem from the OP’s perspective is a bad motor.
It might be the selenoid contacts going bad. But yy guess is that the motor windings are on the fritz, and somehow being affected by the temperature due to the insulation being cracked, etc. ;i.e. you need a replacement starter motor. It could however be something more simple, an electrical connection that is being affected by the engine compartment temperature. Possible due to thermal expansion of the parts. The resistance of these starter motor connections have to be very low, on the order of a few 1/1000’s of an ohm for the thicker of the two wires, to prevent voltage drops big enough to stall the motor. No harm done to double check the connections at the battery and both connections at the starter motor, as well as making sure the starter motor mounting bolts haven’t worked loose, which would increase the resistance to the motor ground.
I agree with everything everyone else has said, and would add that if the timing is too far advanced on the motor, it will crank pretty hard due to the engine kicking back against the starter.
First, thanks for all the responses. My reason for asking the question the way I did was to imagine what I could do short of replacing the starter. It’s a tired old van and it’s not going to last much longer. No need to be putting money into it if I don’t have to.
Besides, it’s an opportunity to learn something.
Yes, there is no question the starter is getting hot from the exhaust pipe. There’s also no question that even a bit of cooling time makes things better. So I’m not buying the increased compression explanation.
Lots of good answers above.
I just want to mention I remember reading Smokey Yunick’s “Say Smokey” column about this issue in Popular Science when I was in jr. high school in the '70s.
A google search for “say smokey popular science hot starter” turned up a number of his articles.