So what did you do to your GMC today?

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Just ran the engine and watched the fan clutch. When I shut down the engine, the fan clutch continued spinning for maybe 2 seconds. Correct me if I am wrong, but shouldn't the fan have stopped spinning almost immediately?
 
Just ran the engine and watched the fan clutch. When I shut down the engine, the fan clutch continued spinning for maybe 2 seconds. Correct me if I am wrong, but shouldn't the fan have stopped spinning almost immediately?
not really. if the engine was hot and the clutch was engaged it would stop faster, but otherwise I think it would coast for a few seconds
 
Just ran the engine and watched the fan clutch. When I shut down the engine, the fan clutch continued spinning for maybe 2 seconds. Correct me if I am wrong, but shouldn't the fan have stopped spinning almost immediately?
A couple of seconds after shutdown for the fan to stop spinning is about right.

This will help with your diagnosis:
 
I had to let it sit and cool down, and after maybe 10, 15 minutes, it fired right up.
Maybe suspect the HEI ignition module. Its inside the distributor at the top rear of the engine where it gets mighty hot. Its a known issue for them to go faulty when hot, then recover when they cool off (thermal intermittent) Make sure you apply heat sink compound to the bottom of the new module before installing.
 
Finally the time has come to begin installing interior stuff instead of taking everything apart. Woohoo.
This dude started with good bones but with some water damage, ware and tear and 47 years of hanging around it needs some love.
This was the beggining:
IMG_20260401_113653_337.webp

Leaks discovered, sealed new wiring scheme being applied and updates to the insulation:

IMG_20260413_124536_860.webp

Help from the wood shop and all of the damage has begun to disapear:

IMG_20260401_113751_154.webp
 
Finally the time has come to begin installing interior stuff instead of taking everything apart. Woohoo.
This dude started with good bones but with some water damage, ware and tear and 47 years of hanging around it needs some love.
This was the beggining:
View attachment 18334

Leaks discovered, sealed new wiring scheme being applied and updates to the insulation:

View attachment 18336

Help from the wood shop and all of the damage has begun to disapear:

View attachment 18337

Beautiful upper cabinet!!
 
Just checked the radiator. The coolant is up to the top. So it checks out. I'm guessing vapor lock. Any ideas on how to prevent this from happening tomorrow?

Do you have a lift pump plumbed before the selector valve?

If you wire it to the 12v at the valve, when you hit the reserve tank switch it will both switch the valve and power your lift pump, this puts a small pressure on all the lines between the lift pump and the engine mechanical pump. This will eliminate 95% of your vapor lock problems in hot weather.
 
Finally the time has come to begin installing interior stuff instead of taking everything apart. Woohoo.
This dude started with good bones but with some water damage, ware and tear and 47 years of hanging around it needs some love.
This was the beggining:
View attachment 18334

Leaks discovered, sealed new wiring scheme being applied and updates to the insulation:

View attachment 18336

Help from the wood shop and all of the damage has begun to disapear:

View attachment 18337
Thanks for the thumbs up Y'all.
It has been a productive couple of days. The new 12v circuits for lighting and accessories is coming along and some of the new wall panels and trim for the window shades are up. The walls are being finished in heavy canvas and most of the new trim is PVC.

IMG_20260420_165126_927.webp

Some of the new lighting now works too. Woohoo.

IMG_20260420_165148_504.webp
 
Howdy all,
Still on my way to the Rally. I had two more incidents today. This morning I installed an auxiliary electric fan to push more air through the radiator. I really thought that worked because it ran great for hours. But, alas, same thing again.

I was able to get online tonight (after 7 pm) and saw some more ideas. I did bring a spare HEI Ignition Module. I'll try changing that out before I set out for the Rally tomorrow. I'm only 3 hours away now, I think.
 
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