Truck won't start when hot

[Bruin_26]

Hey guys, so I'm having a frustrating problem with my '72 C20. It simply won't start when it is hot. If I turn the key after having driven around for awhile it won't do anything! No turning over, no clicking, nothing. Interestingly, if I turn the ignition to the "on" position then bridge the contacts on the starter with a screw driver it starts right up without a problem. It has a 350, 4 Barrel quadrajet, HEI distributor, rebuilt starter, good battery, new ignition switch, new battery cables.
Looking forward to any suggestions and advice and thanks in advance!

[geezer#99]

Several cures available!!
You'll get suggestions like---
Clean all the wire contacts.
A new mini starter.
A heat shield.
And on and on!!!
My cure is wire in a ford solenoid.
https://www.youtube.com/watch?v=SgValPjmogw

Works all the time, anytime!

[Sklptrljay]

Put a relay in. $5 at the auto store.

[NoNeck]

Did you replace the solenoid when you installed the rebuilt starter? Is your starter a High Torque model or the standard version. I have attached a photo showing the difference.

The standard starter motor has the solenoid screwed directly to the metal strap that leads inside the starter motor. This type of starter is shown on the left in the photo.

The High Torque version has a spacer bushing and a long screw connecting the solenoid to the metal strap leading inside the starter motor. This type of starter is shown on the right in the photo.

I would use a quality AC/Delco solenoid, too. They hold up better in extreme heat conditions such as headers and 95° summer days.

Just my .02¢...

POP

[Mike C]

If it's heat soaking it probably wouldn't start with a screwdriver jump either. I would be checking the wiring back to the star side of the ignition switch as well as the park/neutral safety switch.

[Grumpy old man]

I'd bet a donut it's the solenoid

[In The Ten Ring]

Originally Posted by Grumpy old man

I'd bet a donut it's the solenoid

Do you really like donuts or do you have a bunch you don't mind losing?

I'm just picking on you! I have limited understanding of the ignition system.

[custom10nut]

If you have the original wiring.
Run a bypass wire to jump the purple wire on your ignition.
Run the truck and see if that fixes the issue.
If it does, then it's a break in your purple wire, the casing expands when it's hot, and separates causing the break in continuity, until it cools and reconnects.
This happened with mine years ago, and an older gentleman told me how to fix it. It's been working fine since.
Back in the 70s, I remember the same problem happening on the first gen HEI distributors.
The problem in both cases is caused by the constant flexing breaks the wire, and the heat expands the plastic coating causing the gap.
Hope this helps

[davepl]

If it's not the solenoid:

Purple wire.

You have a cut or splice in the purple wire that feeds the ignition, or other damage that is ruining its ability to carry current. It could also be in the neutral safety switch, but more likely the wire has been cut and spliced poorly at some point.

Seen it several times, and watched people throw solenoids, starters, Ford parts, and ignition switches at it.

I see this about once every 2 weeks on these boards, I should just write a page and stick it up on the web somewhere!

The Ford solenoid will "fix" this by bypassing it, but its not the actual fix.

[Bruin_26]

I appreciate everyone's input and yeah I figured that it couldn't be heat soaking considering that I could still start it with a screwdriver. I will look into the wiring and look for any physical break in the connections.

[72oldblu]

Mine did the same thing ,I have headers which is part of the problem, my buddy has a 67 Camaro that does it too, we simply changed out starters, I put a smaller Bosch starter in, an voila, it starts great now, I just did this yesterday,change the starter!

[davepl]

Originally Posted by 72oldblu

it starts great now, I just did this yesterday,change the starter!

But his starts if he can get current to the solenoid leg (like with a screwdriver) so it's not his starter. Might not have been yours either, some solenoids have lower current requirements. Hard to say.

[72oldblu]

I had to use the screwdriver method too,my new starter is way smaller an more torque, it worked for us, I was gonna install a jump button in the cab to override the solenoid, but the new starter for 85 bucks works great, drove it all day yesterday an it started everytime I stopped, while the old starter would always fail when hot.

[tutone]

Before you spend a bunch of $$$ chasing gremlins, run you a heavy ground to a manifold or header bolt from your battery ground post, in addition to your normal ground.. Bad ground connections cause this as well. If that fixes your problem, then clean all connections and ground to the engine. Good luck.

[davepl]

Originally Posted by tutone

Before you spend a bunch of $$$ chasing gremlins, run you a heavy ground to a manifold or header bolt from your battery ground post, in addition to your normal ground.. Bad ground connections cause this as well. If that fixes your problem, then clean all connections and ground to the engine. Good luck.

You're absolutely right that it can (and I guess could) be ground, but it started with a screwdriver which means overriding the solenoid line (purple wire) with full current causes it to work. If it was a ground issue, I don't think it'd help - unless it was so close to marginal that the additional ground provided -just- enough extra current/voltage.

[ga-stepside]

If it is heat soaked the problem is the purple wire can't carry enough current when the solenoid is hot. That's why the screw driver works. A high torque mini starter will usually fix it but so will adding a Ford type fender mounted solenoid and using the purple wire to engage the Ford solenoid and running a big wire from it to the Chevy solenoid.

[Bubba4spd]

Mom had a brand new yellow 1979 L-82 Corvette that was bad about this. Would be embarrassing but I learned not to try to restart it till the starter had time to cool off.

[gangforward]

Had same problem after header install - I put in high torque starter, heat shield and circuit, never had a problem since, even after sitting in traffic in 100 degree Georgia Summers. Big Difference.