How much heat soak is normal?

I have 1994 Chevy V8 pickup, and the vehicles runs perfectly fine when running. If I shut off the truck when its warmed up and start it back up again after only a few minutes of sitting, the temp gauge will climb way up, almost into the red zone, but will very quickly drop back to normal after just a few seconds

I have 1994 Chevy V8 pickup, and the vehicles runs perfectly fine when running. If I shut off the truck when its warmed up and start it back up again after only a few minutes of sitting, the temp gauge will climb way up, almost into the red zone, but will very quickly drop back to normal after just a few seconds of driving. Is that normal? I understand what heat soak is, but I don't think it should be that much, especially when the temperatures are only in the low 70s at the moment.
Yes, after a few minutes, the gauge will rise with the key in the on position and engine shut off, but it will rise even higher than that after it first starts up, like past the 3/4 mark. When I start the engine, it will rise in the first 20 – 30 seconds of running, but then quickly drops back to normal after

Yes, after a few minutes, the gauge will rise with the key in the on position and engine shut off, but it will rise even higher than that after it first starts up, like past the 3/4 mark. When I start the engine, it will rise in the first 20 – 30 seconds of running, but then quickly drops back to normal after another 10 or 15 seconds and stays in that range. BTW, the thermostat was just replaced.

Other answer:

paul h:
Could be normal but it could be excess heat buildup in the heads from a bad pressure cap or a steam pocket from a leaky head gasket. Do you see any white smoke from the exhaust while driving? That indicates a head gasket leak but slight leaks may not show up or be hard to detect.

What may be happening is that when you turn off the truck, the heads are still hot and can overheat/turn to steam if the boiling point of coolant is too low from a faulty radiator pressure cap. A bad head gasket may also cause steam pockets in a head. A 50/50 mix of coolant /water boils at around 223F…a 15 lb pressure cap raises that to around 260F. When you turn off the truck, the heads are still hot and need coolant in them to cool down. Most engines run at around 195-210F operating temps so 223 boiling point does not leave much room for overheating/steam buildup which is the reason for a pressure cap to raise that boiling point .If the boiling point is too low from a bad rad cap, then steam can build up in very hot cylinder head areas and raise the temps near the temp sensor location until you start the engine and get coolant flowing again. Coolant in the engine/system after it's turned off also circulates in the cooling system/radiator due to convection currents until the t-stat closes. Some cooling systems/PCMs also allow or time the rad electric fans (if so equipped) to stay on for a brief period after the engine is turned off to help cool down the engine. Not sure if your model does that.

Given the age of the truck, you may need to flush the cooling system for better circulation/flow and I'd replace the radiator pressure cap…check for head gasket leaks/pressure test the system and bleed any air pockets in the system which may be present after repairs or low fluid levels. Check the cooling fan operation. Perhaps run the engine a bit before turning off to help cool down the heads after driving and see if it helps.

bob:
Heat soak refers to turbo/intercooler issues.

I wonder if your temperature sensor sender is positioned high in the engine… when shut off, the hottest coolant rises, so when you switch on again, that sensor is sitting in artificially hot coolant… as soon as the water pump begins circulating coolant again, the indicated temp drops.

What happens if you shut off, but then turn the ignition back immediately to "run", but with the engine off… so the electricals are working, but the engine isn't running. How does the temp gauge behave… does it slowly rise over the course of a few minutes?

Bill:
It's normal.
bob f:
you may need to burp the coolant system. a sender will spike when it's in air.