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1996 S10 is killing starter solenoids

I have a 96 S10, 2.2 auto. I replaced the engine last September, and put in a new starter because the bendix was bad. The truck ran fine until December. One day it just wouldn’t start. Turns out the solenoid failed. I replaced the starter. The same thing happened again in Feb, and again in march, and has just happened again.
the symptoms: With no prior warning or indications of problems, you hit the key, and can hear the relays on the firewall click, but the starter solenoid makes no noise. I have confirmed I am getting 12 volts through the switch wire all the way to the solenoid, and 12 volts through the battery connection. So I have power to the solenoid. The terminals on the battery are clean and tight, and there is a solid ground connection from the motor to the frame. It’s not an alignment problem, the starters are stamped “No shims required”. The solenoid is not remaining engaged after the engine starts, once the key is released to “run”, power drops out of the relay for the starting circuit.
What could cause the solenoid to fail in just 4 weeks?

Have you tried different brands/ sources for the starters, or were they all identical?

Is this started mounted near the exhaust or exhaust manifold… Its possible there should be a heat shield there, and its gone. I had a similar problem with my old 454 towtruck… Turns out the heat shield was missing, and I had have a new one fabricated.

The starters are from 2 different sources. I am second owner of the truck, (bought it in 99) it didn’t have a heat shield originally, and between 99 and 2011 I only replaced the starter once, so before this most recent series, heat apparently was not a problem.

Put a voltmeter on it. Put the positive lead of the meter on the POSITIVE battery terminal. Put the negative meter lead on the solenoid’s lead coming from the ignition switch. Read the meter WHILE TRYING TO START THE ENGINE. the meter should read very close to zero. If it doesn’t you have a voltage drop between the battery and the solenoid. You’ll need to find that drop; it’s your problem, and it’s probably a crusty connection somewhere.

If it does read nearly zero leave the positive lead on the POSITIVE battery terminal and put the negative lead on the large solenoid lead coming from the battery. Try to start it again while watching the meter. Again, you should read nearly zero. Much more than about 0.1 or 0.2 volts means the battery cable is bad.

If you read nearly zero put the negative lead on the lead that goes from the solenoid to the starter. Watch the meter again and try to start it. If it’s not nearly zero you have a bad solenoid.

Somewhere along the line you should probably check the ground too. Put the meter positive lead on the negative battery terminal and the other lead at the other end of the negative battery cable. Try to start the engine. If the meter doesn’t read pretty close to zero you have a bad NEGATIVE battery cable.

JayWB, thank you for the suggestions. I will definately try the first one to test the power to the solenoid, but there really is no need to test the solenoid itself. It’s already well established it has completely failed. I’m just trying to solve why this is happening over and over. I’ll do the other tests this weekend after I swap out another starter.
In another forum, there seems to be an opinion taking root that these solenoids are failing because of the close proximity of the downpipe for the exhaust. I’ll be wrapping the exhaust when I swap starters.

It’s already well established it has completely failed

How exactly have you established this?
Just because replacing it time and again makes the problem go away for a while this is no assurance that the solenoid is truly the problem.

“How exactly have you established this?” Because it doesn’t work.
I can put power directly to the solenoid, bypassing the control circuit completely, and the solenoid does not engage.

Once I replace it (again), I will follow your tips to troubleshoot the remainder of the electrical side.

Recent engine change and then electrical problem. Could be one or two grounds havent been put back on. Look around the head and maybe the bell housing area. If you see no wire from engine to body that’s just hanging, you could make one and connect it somewhere…

Before replacing the solenoid again check the ground as I’ve explained. It sounds very much to me like you have a very poor ground, probably through the exhaust system. When you get under the car to replace something you disturb things enough to make the poor ground work for a little while. Then it rusts over and there is no ground at all.

Your ready belief in the incompetence of someone you have never met is amazing.
There is one strap from the engine block to the frame on the driver side, and the negative battery cable bolts solidly to the block on the passenger side. Neither are anywhere near the starter.
That was one of the first things I checked. And it has been double checked.
When the starters are returned for exchange, they are bench tested. The solenoids do not work.
It’s not a random ground issue.

I’d be curious enough to tear down one of the failed starters and examine the innards of the solenoid to find how it failed. That might give you the clue you need.

I agree. I’m going to pull this one apart and see if it provides any clue. Besides, I can get a replacement soleniod for half the price of a new starter, so I will have a backup ready to go if I don’t find the cause this time around.
I’m still wondering if the proximity of the exhaust pipe has anything to do with it. You wouldn’t think so since it’s worked fine for 13 years.
I do plan on doing the testing JayWB suggested to make sure the power from the key is correct. New starters do have a little tag indicating a specific minimum voltage. (I don’t remember the exact voltage, it’s been a few months since I saw it).

Is it possible that originally there was a heat shield on the downpipe/manifold, and at some point it fell off?

There has not been any heat shield in the 13 years I have owned the truck.