I've posted this issue before and haven't had a resolution yet so I wanted to try one more time. I've got a 2004 F150 5.4v V8, it's a reman motor with about 30,000K on it. If the outside temp is high (90 degrees or above), my truck will start running hot but if I put it in neutral, it goes back to normal. I've hooked up a code reader and it's throwing P0420 (catalyst system below threshold bank 1) so I'm thinking my passenger side cats are clogged and the build up of back pressure is what's causing the truck to overheat. New water pump was installed when reman engine was dropped in. I've checked the top radiator hose and I can squeeze it easily when the truck runs hot. Anybody with more knowledge care to chime in?

 

Are the hoses hot after engine warm-up and some revving?

 

Moved to 2004 - 2008.

 

If you can squeeze it when hot...something isn't right

 

I thought that was a good sign, as it meant there wasn't a clog?

 

They have some heat to them but I can still touch the top hose and squeeze it some without burning my fingers

 

If the thermostat is open, that upper hose should be very warm to hot, as the water from the block is flowing to the radiator.

Was the thermostat replaced? Its possible that the thermostat is sticking, even on a new or reman engine.

But before I bother with this, I'd go the route of the P0420 code first.

 

I'm have my cats tested next week, I believe they're clogged and the back pressure is causing the over heating