Heat output of an engine to the radiator ??

[cptsideways]

I have a rough idea that effectively its 1/3rd of the engines output in hp. But has anyone got any actual figures?


For a 5.7 small block if you like As that is whats in my boat & I need to to size a heat exchanger for an enclosed water cooling system.

[H-Man]

On my prizm, it took a power output of ~43hp in 100F air doing 70 MPH up a 5% grade with the AC on, the upper grill blocked, and the car loaded down to 3200 lbs to exceed the thermal capacity of the radiator. To make 100 HP hours of mechanical energy, you have to put in almost 400 hp/h of fuel on most engines.

[JRMichler]

A good rule of thumb is that 1/3 of fuel burned goes to turn the crankshaft, 1/3 as heat to the radiator, and 1/3 as heat out the exhaust. This would apply to an automobile engine running near its best efficiency point.

Sample calculation:
Assume your engine burns 10 GPH at WOT.
Assume gasoline is 120,000 BTU per gallon. That sounds about right, I'm too lazy to look it up.
Then heat to radiator is 1/3 X 10 X 120,000 = 400,000 BTUH.

A large diesel engine can convert as much as 50% of the fuel into power.

[user removed]

^^^^ Precisely what I have read.

regards
mech