Fuel addition to warm truck engines??

[akghound]

We are using coolant heat exchangers to pre-heat wash water for pressure washers on trucks. The mechanic tells me that when the coolant drops to somewhere below 130* the on board computer adds fuel to warm up the engine. The engine is set to run at 1000 RPM while washing, to power the pump via PTO. My question is how does the computer add fuel without increasing RPM. These are International 366 engines. I claim he is mistaken. It does add fuel at an idle at lower temps, thus increasing RPM but at 1000 RPM I doubt that any additional fuel is added to warm the engine. Can anyone please weigh in on this discussion?
Thanks .... Ken Gardner

[mobile_bob]

when you add fuel you gain rpm, unless you add fuel and alter the timeing which
is unlikely in light of epa concerns.

the tstat should keep the engine operating temps up in most cases, unless you are in very cold
ambeint temperatures, or you have your heatex inserted into the engine loop taking heat out
of what normally is the tstat controlled inner loop of the engine.

the only time i see engine's adding fuel is upon cold start up and we see an increase in rpms from
650  to 850-900rpm for several minutes after  startup.

i suppose it is possible depending how the heatex is plumped into the system, if it is in the heater loop
you may very well cool the engine sufficiently while sitting running at idle and cause the computer to
add fuel to warm things up,, if this is the case you will notice an increase in rpm as well.

bob g