86 F-250 460, solenoids keep getting stuck so starter stays engaged. I have put 10+ solenoids in last year. Am I missing something here or is there a common problem that may cause this. I have replaced starter 3 times just to make sure it isn't the problem. I know stuff isn't made like it use to be but I would think I would get one good one out of 10 plus.

 

I'd make sure the cables are fresh and connections to block and frame and firewall are bulletproof. Supposedly neglected grounds contribute to this. Here's how to test

http://www.aa1car.com/library/voltage_drop_testing.htm

 

There has also been posts to use Motorcraft part and not a parts store one.
Or one from a junk yard but you don't know if that has been replaced or not.


I wonder if a marine one would be any better? Thinking a lot more money just don't know if better?
Dave ----

 

Went through a series of solenoids myself until I replaced the hot battery cable from the battery to the solenoid with a brand new heavier gauge cable after reading somewhere that old cables can corrode internally, causing internal resistance and thus causing solenoid problems.

I've had people question the battery cable theory but since changing the cable the NAPA mileage plus solenoid I've got in there now has held up for a couple maybe three years now.

 

Wow, what brand(s) are you using?

 

I don't doubt your problem hasn't returned, but the new cable thing had me scratching my head. I was one of those skeptics.


I have an idea of what may have been happening. Let's say the suspect cable was dropping a certain amount of available voltage when under load. This would certainly cause a slow turning starter, but why would it damage the solenoid? The suspect cable was acting like a giant resistor, and actually decreasing current flow through the solenoid contacts, not increasing it. Less current flow should equal less potential for damage.


Then I realized the reduced voltage at the solenoid contacts also means less voltage available to the solenoid coil, the electromagnet that actually moves the contacts. Less voltage on the electromagnet means less clamping force on the contacts, and thus more potential for arcing. That's a bingo! That's my theory, and I'm sticking to it...

 

I think maybe the high resistance in the overall starting circuit probably causes the switch contacts (that's basically what a relay or solenoid is) to get "sticky" or more or less arc weld themselves together.

 

Less volts = more amps
More amps = arc weld the solenoid contacts!


That's my story and I am sticking to it
Dave ----

 

I had tried diode suppressed, silver contact, continuous duty.......

Switch to a '90's truck PMGR starter and never have to deal with this again.

 

No, Less volts = less amps

 

If your starter motor is 2000W, it doesn't care where the power comes from.
12V x 166A or 8V x 250A.
It is going to draw what it needs.

 

Yes it will draw as much as it can, but less volts means less amps.

 

How come you look at the same HP motor wired for 120v or 220v how come you have lower amps on the 220?


I believe it is the same for lighting for the same watt light.
That is what I was basing it on.
Dave ----

 

You should be able to look at the ID numbers on it, it should have a oval on it someplace if it's an OEM part.

 

Gentlemen, it may be time to put on my orthopedic diplomat's hat and say everybody is correct in regards to voltage vs. amperage. Sort of. Under certain specific conditions. But in some ways we are comparing apples to oranges.

Let's look at the amperage increase when the voltage is lower. For example, with an old 6 volt vehicle. In the 1950s, auto makers converted en masse from 6 to 12 volt systems. One huge advantage was amperage was halved to do the same amount of work (wattage). Less amperage meant much smaller conductors could be used, leading to huge cost savings.

Consider a 6v vehicle with a certain size engine. The 6v starter might have drawn 300 amps, a number I picked out of thin air. I'm too lazy to do the math, but the 6v starter consumed X watts to spin that engine. Next year's 12v model may have still had that same size engine, and it still required X watts to spin it at the same speed. Only now, thanks to the increased efficiency of a 12v system, the amperage is halved to only 150 instead of 300. So whoever said amperage rises with lower voltage is correct. Here's the catch: It's only in that type of situation. There's some factor at play but I'm not quite sure what it is. Maybe it's only when the conductors are in optimal condition or something like that, or how the measurents are taken.

Now let's look at our actual scenario, a 12v vehicle repeatedly burning up solenoids for reasons unknown. One poster who also was going through solenoids mentioned an undersized cable that seemed to be acting like a big resistor. Replacing that cable worked for him. Let's run a controlled scientific experiment. I've got an old VAT-40 carbon pile load tester. For those unfamiliar, it's basically a giant variable resistor that can handle huge amounts of current. Imagine I've removed the short cable that runs from the battery (+) post to the starter solenoid. In its place, I've connected my VAT-40 in series so all current has to go through it.

I'll begin by adjusting the VAT-40 to zero resistance, so it mimics a perfect battery cable. I'll engage the starter and take an amp reading as a baseline. Let's say it draws 150 amps. Bear with me. Next I'm going to adjust the VAT-40 to ADD resistance into the circuit, to mimic a faulty cable.

With extra resistance in series in the starter circuit, raise your hand if you think the amperage will increase. Thank you, the raised hands makes it easier to know who to slap. The starter will turn at a slower pace. Amperage will decrease, not increase.

I'm going to dial in even more resistance. Anybody want to guess what will happen? Pat yourself on the back if you said the starter will slow down even more and the amperage will decrease. Eventually I'm going to dial in an infinite amount of resistance (an open, same as if I'd disconnected the cable completely). The starter will not even try to turn and amperage will be a perfect zero.

Now if I had connected a voltmeter across the starter, you'd have seen the available voltage drop with each successive test as the series resistance was increased. Only in this case, the amperage also dropped as the voltage dropped. So whoever said amperage would drop as voltage dropped was also right. Here's another caveat: Only in this scenario.

Clear as mud? Maybe the missing factor will come to me in a dream tonight. And then I can add some dramatic conclusion that ties it all together with the toasted solenoids.

Semi-humbly submitted.