Quote Originally Posted by LeMarky Dissod View Post
Depends on ambient temp?
Long ago, equipped with an Meziere HD H2Opump (>48GpM if you ask Meziere), parked atop a long steep hill, I tried something stupid on a 23°F / -5°C winter's day.

I started the wagon's LT1 with the electric H2Opump disconnected.
When the dash temp gauge needle hit 230°F / 110°C, I repowered the H2Opump and rolled downhill, both fans staying on til the H2Opump temp sensor was under 203°F / 95°C.

From 23°F / -5°C to 230°F / 110°C took a wee lil bit over 7min. (Despite the stupidity, engine lasted another 125K miles, 255K miles total.)
On a record hot desert day, I'd guess 3min or less?

Important note: I'd previously familiarized myself with the correlation between the H2Opump temp sensor & the dash temp gauge needle when the engine was equipped with an OE-type mech H2Opump, a 525RpM idle, and fans set to turn on @ 235.4°F / 113.00°C?
IMEO, if the dash temp gauge needle hits 'the red', it may already be too late. Get to know your dash temp gauge needle personally before trying this stuff.
I don’t think I could compare your description here with my question because in your case the water (coolant) was present in the water jacket, even though you had no pump function. So even without a pump, the fluid in the head would absorb some heat. My question assumes there’s no water or coolant in the head.

It’s not a big deal really. I can put it back together without running it any longer than the 10 seconds I already did.

I was just wondering what a safe run time might be for an LT1 aluminum headed engine with “no coolant” might be.