Ok so I've had this problem for a while.

At first I had no heat and the gauge would drop to cold until I switch the A/C **** to OFF (closing off heater core) and then get the engine to rev. Upper radiator hose gets hot.

The inlet hose to the heater core got pretty warm (not as much as I would think it should be). So I tried back flushing the heater core.......nothing.

Back in December I took out the thermostat and replaced the housing. Then I flushed the system using the Prestone Flush N Fill kit. Then drained. Then added the Prestone Flush mix. Ran the engine for a while. Drained it. Then replaced the thermostat with a new Motorcraft thermostat (I think it was rated 192). Nothing.

Then I replaced the heater core. Got a little heat but still it would drop in temp and on the gauge until i switched the **** to off.

Each time I've tried to get all the air out of the lines. Even filled to the top at the heater hoses using the Flush kit port.

I don't know what is going on here. Could my water pump be getting weak where it cant produce enough power to flow fluid to through the heater core? Or is my thermostat too low of a rating (its only 3 degrees less than stock).

When I flushed the system it contained a lot of sediments and rust particles. Could this be parts of my water pumps impellers?

 

im thinking what your thinking

 

You talking about the impellers being rusted away?

 

Ok so I got the problem solved today. Turns out it was the water pump and the impellers were GONE!

Take a look at the new and old:

 

holy **** gone is right lol

 

Actually its hard to see this but the impellers are still somewhat there, they are just bent back. Evidently the disk that is on the outside disintegrated and the blades wore down so thin that the rotation caused them to bend backwards.

Evidently the 2.5L stays pretty cool when it has little coolant flow, then again im sure the fluid moved around pretty well using convection.

 

WOAH, mine was not half that bad when I pulled it.

 

How many miles was on your truck when you pulled it......mine is right at 170k

 

At least you found the problem before you overheated! I would definitely put in some of the coolant stuff that Royal Purple has made for the cooling system, it works great for me.

 

How much was that part?

 

45.99 at o'reilly's plus 10 core. Lifetime warranty It came with two new o-rings too. One for the inlet tube and one for the pump itself