Truck is a 98 F150 4.6 with 153k miles. The other day I noticed a ticking pulley (pretty sure it's the A/C) and when I popped my hood to take a listen (after a 3 or so mile drive) I noticed my top radiator hose was cold and very very firm. Opening the overflow cap relieved the pressure but coolant still wasn't flowing.

I drained the system enough to pull the t-stat and checked it and it's opening just fine. The water pump appears to be working since it drew the overflow level down just fine when I refilled the system after putting the t-stat back in. Head gasket leak seems unlikely since I have no coolant in the oil or vice a versa. The truck warms up to normal operating temps and isn't overheating. I have heat out the vents also. Any ideas?

Also, is there any way to rig the serpentine belt to bypass the A/C entirely? From my searching people seem to think it's possible but I've never seen a definitive answer from someone who's actually done it.

 

Slip the belt off & spin each pulley by hand or with shop air to find the noisy one. I wouldn't try to bypass anything. At worst, I'd pull the bad pulley & replace it with a junkyard part. If it's the A/C pulley, you don't have to open the refrigerant system to replace that pulley.

Try removing the t'stat temporarily to check for flow. You won't see any in the degas bottle because it's not in the main circuit. Leave the upper hose loose on the radiator, start the engine with the pressure cap off, and slowly pull the hose back to see how much coolant is moving. Don't let it splash in your mouth or eyes. Don't let the engine warm up. Reinstall the t'stat.

 

I should have mentioned that I'd already pulled the belt and checked the pulleys beforehand. All turn freely without any noise. None have any play with the exception of the PS pump and the A/C. I was told that a little play in the PS pump was fine and isn't the A/C supposed to have play?

Anyway, I just pulled the t-stat and I have great flow with it out. I know the t-stat is opening because I tested it in a pot of near boiling water. It it possible that the radiator cap could be causing this? If it's stuck closed could it be allowing pressure to build up in the system and prevent the thermostat from opening?

Oh, one more question. Since I'm messing around with the coolant system I'm going to do a flush and fill. I've usually just drained and refilled but this time I picked up one of those Prestone kits for flushing they system. Problem is I don't know which of those hoses going/coming from my heater core are which?

 

No, the compressor pulley should be relatively tight & smooth, but spin VERY freely. At most, it might move straight in-out less than 1/16", but it shouldn't wobble or twist at all.



The cap is supposed to hold pressure - that doesn't affect flow in any way.

I wouldn't cut into any of the hoses - I'd return that kit. If you want to flush the system, leave the t-stat out, disconnect the upper hose at the radiator, stick a garden hose into the radiator, and start the engine. It'll pump everything out onto the ground (coolant puddles are toxic, so rinse them away immediately). When it runs clear, you can drain the water & refill with the correct coolant mix. But the hose connected to the intake manifold flows OUT to the heater core; the one that runs under the intake to the pump flows IN to the engine.

For more info, read this Cooling System article.

 

I already installed the kit. Maybe I'll regret it in the future but it's done at this point.

As to the cap, it' only supposed to hold pressure until 16 psi iirc. Then it's supposed to bleed off.

Anyway, any other suggestions? The pump pumps, the thermostat opens, and the truck warms up, but coolant doesn't circulate. I'm at a loss here.

 

Did you burp it ?

 

are you sure the system is full? The reservoirs can be mis leading. You need to fill it right up to the top of the cold fill mark.

 

Yes I'd burped it and yes I'm pretty sure the system was full. After draining to check the t-stat I filled it up to the cold fill line and then proceeded to refill it (keeping it at the cold fill line) as the system drank what I'd already put it. I then burped it while letting it run (with the overflow cap off) for about 5 minutes. Then let it run for about 5 more until bubbles stopped coming up in the overflow bottle.

 

If the last one is true, then at least one of the others isn't happening. How do you know for sure that the pump works? Try this:
Let the engine cool thoroughly so the t'stat is fully closed.
Disconnect the heater core return hose (the one that goes UNDER the intake), and plug the hose.
Connect a new hose to the heater core and route it to the degas bottle.
Remove the throttle linkage cover & start the engine.
Rev the engine and observe the flow from the new hose. Pinch it and see how much pressure/flow it maintains.

 

Would pulling the t-stat and disconnecting the upper radiator hose while filling with water through the degas bottle be an effective test? I really don't want to go screwing around with the heater core hoses as I've heard they're about impossible to get off and the heater core is easy to break.

 

The point of that test is to check flow, at pressure, from the pump. To build up pressure, you need a restriction, and the smaller heater core hoses are perfect. Letting the t'stat close directs ALL the flow thru the heater core. If the pump impeller is eroded or slipping on the shaft, you'll note a drop in flow when you pinch the hose, or a lack of pressure.

No, what you described won't test it.

 

Alright, I did what you described. Well, sort of. I tested at the heater core inlet hose as opposed to the heater core outlet barb. I figured if we're testing for flow and pressure it makes sense to eliminate the possible restriction of the heater core. Not to mention me not wanting to over pressurize the heater core by restricting flow through it.

Anyway, water flows out ok when unrestricted but you can easily stick your thumb over the hose and block it with no apparent buildup of pressure behind your thumb.

Still seems strange to me. I mean, the water pump pumps water out the upper radiator hose just fine with the thermostat removed. I guess the thermostat restricts flow just enough that it's too much for the pump to overcome? Ah well.

Anyone have any advice for what water pump I should go with? I've seen some people use pumps of Navigators. Remanufactured or new, etc..

Oh, and thank you for all your help and advice.

 

The water pump impeller is probably eroded, or VERY loose on the shaft.



Buy either a MotorCraft or one of the more-expensive options from NAPA/CarQuest/Parts+Plus. Stay out of the zone.

 

Not saying that what Steve suggested isn't the case, but isn't there a restrictor in that heater hose? Impellers don't come loose very often, but I have seen 'em. Removal of the W/P isn't a world class job, I think if it were my truck, I would remove the W/P 1st to see if either of those possibilities is the case. If no erosion of the impeller and the impeller isn't loose and the pump doesn't leak, there's not much else to go wrong with it, since you didn't say anything about noise. I agree, if it needs a pump, I would follow Steve's suggestion.

 

Ok, so I just picked up a new pump and pulled the old one off. And it's fine. No significant impeller deterioration and the impeller doesn't slip at all. Now what?