Need some help. 4.6L overheating with weird symptoms.

[JC316]

I don't know why I always get the tough jobs, but this one has me mildly stumped. Picked up an 01 Expedition from auction with the 4.6L in it. It has no heat, which I'm sure is a heater core, but that shouldn't be causing these symptoms.

It can idle all day long just fine, but if you drive it, or rev the engine up at idle, it will start to overheat. The coolant in the reservoir starts bubbling violently like it's boiling, but the temperature of the fluid is only 190*F. The upper hose is pretty soft, even with the T-stat open, until it starts overheating or you rev the engine up. Radiator appears to be new, as does the T-stat. If you rev it with the cap off, it will puke coolant out, but when you kill it, it all gets sucked back in the radiator. The radiator fins aren't hot in the slightest and the lower hose barely gets warm.

My next thought was head gasket, but there is no white smoke or water in the oil. Got a block tester to be sure, tested it twice and it was good. I have a code stating that the cylinder head temperature was too high.

My only thought is a big bubble in the cooling system, but you would think that as much as I have revved it up, the system would have been burped by now. Since I got this car from auction, and I know it was repoed, I'm not ruling out sabotage, but I don't know of anything in the cooling system that would cause this.


Any ideas?

[Craizie]

Is the capacitor fluxing?

[JC316]

Is the capacitor fluxing?

Yes. In addition to that, the muffler bearings are replaced and the blinker fluid has been topped off.

One other weird thing to note. The heater line coming off the intake is hot up to the point where it T's off going to the front and rear heater cores, once past the T, the lines are cold.

[Craizie]

Replace the heater core?

[JC316]

Replace the heater core?

I've had 3 F series with clogged heater cores in the past year and none of them acted like this. It just feeds coolant off from the intake and then back of the water pump, it being clogged wont affect the rest of the cooling system.

[Baron Von Crowder]

It does circulate off the back of the head, it *could* effect cooling and head temp, though I wouldnt expect it to do what you are talking about.

Did you change the water pump or drive belt?

[JC316]

It does circulate off the back of the head, it *could* effect cooling and head temp, though I wouldnt expect it to do what you are talking about.

Did you change the water pump or drive belt?

It could in theory, but I highly doubt it. No, haven't changed those. I guess the pump could have stopped circulating. I will check that out.

[Baron Von Crowder]

It could in theory, but I highly doubt it. No, haven't changed those. I guess the pump could have stopped circulating. I will check that out.

I was thinking it was turning backward.

[JC316]

I was thinking it was turning backward.

I will double check the belt routing, make sure that someone didn't screw it up.

[Mysticcobrakilla]

It does kind of sound like water pump cavitation.

[JC316]

Belt routing is correct.

[JC316]

Well, I am to the point of taking the water pump out. Bypassed the heater core, and borrowed the radiator cap from my dads 5.4L just to be sure. No change in the symptoms. Got to be the pump.

[JC316]

We have a winner. Water pump impeller got decapitated.

[shumpertdavid]

I've had 2 vehicles come in with the impeller rusted so bad that there was little left of the blades. Both times I had very odd cooling system troubles. I've had several that the impeller was made of plastic and cracked where they wouldn't hold the shaft any longer. Glad yours was an easy repair.