Hello hilly,
I get it. I'll bet the majority of used SBCs that had the starter replaced are missing the original heat shield.
But as Schurkey stated the factory heat shields have been installed since forever. To give you an idea of what's missing I
decided to look up your vehicle at a GM parts site:
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Googling starter heat shield 10068600 didn't come back with the exact same part being sold, *but*
it does show a lot of aftermarket heat shields available from the usual sources.
But if you are feeling creative, read this thread over in the jalopyjournal website. There's a thread where
hot rodders that were suffering hot start issues shared their home brewed heat shield fixes. It's a good read: (
Starter Heat Shields)
NOTE: They also mentioned the benefits of upgrading old classic direct drive starters to the newer GM gear reduction units.
Re: Heat related intermittent no-crank to other components in the Ignition Circuit.
If you peruse the wiring diagrams, Circuit #6 is Hot only when the Ignition Key is in the START position,
and the Neutral Safety Switch is is either in Park or Neutral positions. (Or Clutch Depressed switch is
closed if you are driving a stick.) This circuit is protected by the 5A CRANK fuse.
On the other hand, the ECM / ESC / ICM are on a completely difference circuit (#439) which is fed by the 10A
ECM IGN fuse. (Hot in Start & Run)
In English, the ICM has no direct influence on the CRANK control circuit.
This is why troubleshooters want to know if the symptoms are 'No Crank/No Start' versus 'Crank/No Start'.
This small behavior detail completely changes which electrical circuit gets troubleshot.
One last possible workaround until you can get the heat shield either bought (or fabbed up) and installed.
If you drive your truck long enough that you think that it's going to heat soak the starter solenoid, simply pop
your hood & raise it fully when you first park the vehicle.
This way, instead of the underhood heat building up and causing the heat soak of the solenoid windings, you
instead get cooling air pulled in from underneath due to the chimney effect. May or may not make a difference,
depending upon the variables, but it's worth a try.
Who knows? You may find a heat shield in the treasure yard on a unicorn GMT400 where a detail-oriented
owner kept reinstalling the heat shield.
When you get the fix implemented, be sure to come back and share the solution with others researching
similar symptoms.
Happy Hunting --