[RichH]

Must be you!

Any ''heavier load'' for the engine to attain the same rpm will require more fuelinput (power). The heat exchanger (at the same rpm and @ constant water pump flow) is a constant heat sink - only ejecting a fixed certain amount (BTUs) ... (yes, the log mean temperature differences LMTD between input and output will be different, but lets not go there at this time). The more fuel to attain the given rpm, the higher the heat load; but, since the exchanger/raw water pump is operating at a fixed condition the temperature will rise in the engine ..... its a simple question of thermodynamic balance.

Whats happening is that the engine is using more horsepower/fuel to attain the same rpm; more fuel consumed = more heat, the exchanger is (essentially) constant in heat removal ability.

Next time you drive your car up a long hill at a reference mph/rpm, take note of the engine temp. Now run the hill again at the same mph/rpm but with your foot on the brakes or pulling a large trailer .... and note the difference in engine temp.(and how much further down you have to depress the accelerator to attain the same mph/rpm).