have a 82[i think] 470 nmercruiser closed cooling that overheats when running flat out.have done new lower pump,thermo-stat,head gasket.have run clear hoses to watch water flow.has anybody have any other suggestions.idling,as expected,does not heat.
im having a similar problem right now xltier, still unresolved. check the diameter of the heat exchanger, the long round thing on the lower left side, it needs to be 4inches. pressure test your cooling system also.
The earlier models had a 3" heat exchanger. Later models had a 4".<br /><br />If you do not have a 4", switch to one.<br /><br />Either way, I suspect the heat exchanger is plugged.
Even with 4" heat exchanger, running flat out can cause hot running conditions unless everythings in good order and there are no obstructions in exchanger and other passages. If engine cools down as RPMs are reduced you're probably running into near normal operating conditions. Run blower continuously to maintain coolest possible engine compartment.
