1993 c3500 454 Motor Won't Crank Over When Warm

I don't know if this applies to your case...

"Defective engine coolant temp sensor

The coolant temperature sensor measures the engine temperature through the coolant and relates this information to the powertrain control module. If the sensor goes bad, it can send incorrect information to the car computer, telling it that the vehicle temperature is too high."

https://rxmechanic.com/car-wont-start-until-it-cools-down/

There is no interlock for temperature on the start circuit, especially as far back as 1993. The ECMs of that era are relatively simple, and that would be far more protection than was in practice, even up to current models.

The engine block temperature will naturally rise as the coolant stops flowing, as the residual heat in the engine block is conducted to coolant no longer being mechanically moved, by your water pump.

STOP replacing parts until you know what the true offending problem really is!

This shotgun shade-tree mechanic technique seldom works the first or second shot.

Do you have (or have access to) an OBD II code reader? The sensor rich environment of the truck exists, in part, to report the nature of problems within the sensor array, this reporting is relayed to interested persons via the OBD II port.

[edit] Ooops… likely not applicable. I now see 1993 model year. OBDII not available, OBD I is spotty.

The most likely causes for your 1993 c3500 454 engine not cranking when hot are a heat-soaked starter motor or poor electrical connections, particularly the starter and ground cables. When jumped, you bypass the faulty circuit or provide enough power to overcome the heat-related resistance, allowing it to crank.

I would start off with cleaning all the electrical connections...then I would check the radiator coolant level, it shouldn't be getting that hot unless something is wrong, I would check the thermostat and water pump, then check coolant flow in radiator when thermostat opens...you might have an air bubble or a clogged radiator, or faulty water pump...maybe flush the system...

No I checked the radiator and its always full. Infact I Installed a new one as well as a new water pump about 1 year ago. I still am leaning to something with the heat sensor unit. As I wrote earlier, before I shut if off I check the heat gauge. and its usually right at 180 degrees. As soon as I turn it off I turn the ignition back on and the temp gauge now reads 200 degrees. this is only within seconds of turning it off.

An infrared thermometer gun can help, I would check the temperature of your starter first...but I would check the water temperature in the coolant hoses for accuracy...

A starter's acceptable high temperature is below 140° as it can be damaged or fail above this point. Excessive heat can cause the internal components to deteriorate or expand, increasing resistance and reducing efficiency, which can lead to a failure to crank the engine. A starter motor will show signs of overheating if it becomes too hot to the touch, potentially leading to wiring insulation burning.

https://us.haynes.com/collections/chevrolet-silverado-3500-hd-car-manuals?

Starter is OK I can jump across with a screwdriver and it spins

You’ve said this twice. What, more precisely, does “… jump across the starter…” mean?

Are you shorting out the posts on the starter solenoid?

When you say “… (starter) spins…”, is the bendix gear engaging the starter ring, or does the starter motor just spin around and that is all?

If you can spin the starter motor by shorting the starter solenoid, and this turns the engine over, if you do this (oh so very carefully!) with the trans in park and key turned to run, she should start up.

What I meant was if I jump across the positive and starter terminal on the relay the starter and motor spin, thus able to start the engine.

You need to check if there is a heat shield over the starter. Starters solenoids don't lioke heat. The fact that you can jump is true. You are putting direct power to the starter term. There is a kit you can buy, or build if you know how that does the same thing. The first thing I would do is put a heat shield on. Then get the kit to rewire this.

I just had a thought. (Yeah, I hear you guys thinkin’ that one over)

I presume your truck is fitted with an immobilizer (anti theft device, uses the transponder key). How long since you changed the key battery?

no immobilizer or key battery.

When jumping it out you may be bypassing the problem, either a bad connection or component, or you might be giving it the amperage boost it needs to overcome a buildup of resistance due to overheating....without a true reading of the starter temperature we are just guessing....have you tried touching the starter to see if it's hot? If you can't hold your hand on it comfortably, it's too hot...

To troubleshoot this problem we need some good feedback, otherwise we're just guessing, have you pulled the plugs? what do they look like, maybe the carb is adjusted too lean...have you changed the oil? what oil are you using...? Is the radiator the proper size? Is the fan moving enough air? How are you checking it? What is the temperature drop across the radiator, incoming temperature minus outgoing temp....?

LOL, I know I am bypassing the problem when I jump the starter. their is something between the ignition switch and the starter solenoid that is the issue. I am thinking a relay that is heating up.

Starter is not too hot to the touch. when running the truck runs fine, no carb has a throttle body injection system (TBI). I can pull my 24 ft boat and trailer with no issues. just cant turn it off until I get to where I am going. when running and driving temperature is 180 degrees.

background on this. about 2 years back was the first time is happened. drove about 85 miles and pulled in for gas. when I went to start it it wouldn't. that's when I discovered I could jump the starter to get it running. this only happened a few times in the year following that first instance. in the last year it has progressively gotten worse, to the point now that if I drive it anywhere over say 25 miles it wont start. if I let it set 20-30 minutes, it starts fine.

I have already replaced the following;

water pump and radiator maybe 1 year ago.

Starter and starter relay about the same time.

I will be switching out the relay under the hood to see what happens.

And no I don't have a heat gun/scope to test different spots for any excessive signatures.

The lower part of these schematics is what he needs to eliminate the problem.

When cleaning electrical connections, do BOTH ends of the ground connection(s). Apparent a lot of people forget to do the frame end.

I agree with the heat soaked starter diagnosis as I have seen the starter solenoid get stuck when hot. Then it cant connect the big current handling disk and throw the spinning gear in to the flywheel teeth. You might hear nothing at all.

If you can get a meter on the starting solenoid control wire (or a buzzer) and have someone use the key to start you should see voltage appear but no starter motor turning because it is seized under heat. I have taken this out and cleaned it with good results before.

If however you get no voltage at the solenoid, then you must look upstream and my next bet is on the anti-theft interlock system. These were complete crap and contributed to many cars going to the junkyard prematurely. if you have this (not sure if C3500 would), there is a small chip in the key and the computer must see it to allow the start signal to continue to the solenoid. There are ways to bypass this with a resistor around 80 ohms as I recall but there are about 12 resistances and it must match. Very temperamental . I had a 98 Olds that I installed a remote starter on with the resistor fake-out on a relay and when the car got older it would no longer work with the key and I had to remote start it. I was always nervous that would break but it didnt. GM got the 3800 engine right in that one but not much else around that time. On this line, clean the key and lock with contact cleaner and jiggle it when you have a problem, or try an alternate key if you have one.

Welcome aboard!

Regarding your comment “… my next bet is on the anti-theft interlock system.“ See comment #16, and the response in #20.

The key resistor is not the same as an immobilizer, as far as I have seen, especially in that vintage. While it might perform the same function, I would never consider that an immobilizer, just an ignition interlock, like an extended function key. No battery associated with that either. Just a resistor, connected to a sensor circuit that measures the resistance.

Yes. GM vehicles in this range of production year utilized a passive ignition key authentication system (resistor in the key blade) called VATS. An incorrect resistor value disabled both the starter circuit and the fuel pump, so even if the starter relay is jumped you will not get far.

I slipped up a little bit, asking about a flat battery in the key. The RFID type of active key authentication didn’t start showing up until about 1997, so wouldn’t be in play here.

OP has stated that an anti-theft scheme of any type, description, or sort (other than a metal key) is not present in this automobile.

Try swapping the plug in starter relay with another relay nearby, in the under hood fuse box. There are usually 1 or 2 other heavier current relays.

The only relay I see under the hood is for the fuel pump.

Could be old enough to be directly wired to the ignition switch.

Thats what I think. with all the people pointing toward the solenoid, I am going to replace it and see what happens. Yesterday I went out to start when cold and got a click but no spin. tried again right way and started no problem. that to me sounds like the solenoid.

i'll let all know how it acts after replacement.

Unplug the temp sensor. I had a similar issue on an YJ. If this solves it, you have a heat soak issue. Flush the block and radiator

A similar problem a long time ago (the car was still under guarantee) and I had the auto shop almost on permanent standby. The shop replaced sensors solenoids etc but nothing solved the problem.

One day I was stranded next to the road and out of desperation decided to cut the wires of the suppressor cap (for radio) and the problems were over.

Best of luck to find the problem.

big block "starter heat soak" | Team Chevelle

This kit includes: 30 Amp heavy-duty relay Relay base with wire harness (4' input, 4' output) Crimp-on terminals Mounting ... It’s a lot cheaper to buy just ford solenoid from a parts store.

Before you go chasing all the different ideas, changing / buying parts STOP.!
Remove the cover and reveal the ignition switch, find the wire which goes from the Start position on the switch.
Run a direct wire from there to the Starter Solinoid. Disconnect the existing wire ( wrap some isulating tape around the terminal so it doesn't short out when you use the test wire ) and replace with this new one at the starter solinoid.
Run engine up to operating temperature ( 180) switch off and try restarting. If it restarts, you have a connecton problem or a broken wire or, if there is a Relay in the circuit a faulty relay.
If it does not restart your fault is in either the Starter Solinoid or Starter motor but as you said they are only roughly 12 months old.
My guess is a Relay or Wiring fault. Quickest way is swop the Relay they are only a few dollars and see if the works, if not, check the wiring.
One question, did the problem exist before you replaced the Starter or only after you replaced the starter ??

Existed before I replaced starter.

So as replacing the Starter & Solinoid did not cure the Problem it obviously lies in the wiring or the relay. Sometimes there are 2-or 3 similar Relays in the Fuse Box. Try swopping your Starter Relay into another position and see if that function operates, if the other function operates its not your relay that's faulty.
Make sure the terminals on the relay and in the Fuse box are clean and not corroded
Then it's down to checking the wiring !!
Just had a thought, where is the ICM located? It could be a electronic component shutting down due to heat, you could run the car up to normal Temp. come home and check you are still getting power etc. to the PCM or blow cold air over the ICM to cool it quick and see if it cranks !
Have Fun !!

This problem can be caused by bad grounding of the starter due to oil leakage getting between the engine block and starter housing. However, I don't think that is the cause in this case because it cranks when you jump the battery to the starter solenoid.

I'd be tempted to blame the solenoid in this case. Next time it happens, have a helper turn the key while you listen/feel the starter solenoid to see if it's actually moving.

My nephew operates a repair shop and he has complained frequently about the poor quality of aftermarket repair parts. He put two aftermarket fuel pumps in my Tahoe; first one failed the next day, second one failed in less than a year. He installed an OEM pump that has been working for a couple of months now.

As previously mentioned, stop replacing parts unless you KNOW they are bad. Even with newer vehicles, a lot of troubleshooting can be done at virtually no cost.

First off, thank you for the update on your troubles. We often never hear back, one way or the other, about a resolution.

Next, congratulations on your success! You are obviously a tenacious problem solver, another trait this forum doesn’t see often enough.

Wishing for you many miles of trouble free motoring,

Doorman

Can you get a wiring diagram for your 1993 C3500? I don't know how advanced your 1993 is but my 1996 Nissan has none of the advanced gizmos, no computer no advanced protection.

Recently I had to replace the starter motor, would not turn over when hot and i found it was the starter motor that had become water cooled and would stop in a position where it would not start. The plastic former in the solenoid coil had also deformed and when hot would not let the steel slug move freely so the contact disk did not make contact.

As for the temperature gauge increasing when turned off, this is normal for the water stops circulating in the motor and usually the temp sender is at the back of the motor further from the thermostat and as the heat comes out of the block the reading rises.