Rod Wise

Thanks! I'll get onto changing my water pump then. My truck is struggling to cool and it wasn't the fan clutch, so I'm guessing it must be the pump. Thermostat isn't very old at all, and flushed system about a year ago. With 163,000 miles, isn't it prudent to swap timing chain and gears as well?

raski

No timing chain on 4.9. It has two meshing gears. I wouldn't worry about them as they last a very long time, if they ever fail.. If you are running hot, I would bet on the radiator, either rotted fins or mineral build up on the internal water tubes.. Other than leaking, I never had a water pump actually cause overheating. It would have to seize or the impeller come apart which rarely happens.

Eric Fullerton

If yours is like mine, and has the upper hose running above the power steering pump, there is a possibility of an air bubble restricting flow. The only way I've found it clear it was to raise the front end about 1 ft and squeeze the dickens out of the upper hose. With the cap off you should hear it when the air burps out. it doesn't need to be running for this.

Rod Wise

Thanks for the reply. Is it possible for this to happen out of the blue? It had been running great, then suddenly starting running hot. Seemed to be getting hot while sitting, then cool down while running down highway at 55. I figured "ah, fan clutch." But after changing out, still runs hot. Now I figure water pump (not much left to change!). I'll try your "burping" as well, but if this doesn't do it, it would have to be the radiator blocked.

Eric Fullerton

I doubt it could just happen out of the blue, but it doesn't cost anything, so as you say, worth a try. You mentioned a fairly new thermostat, and that is exactly the sort of thing that sets it off. I found this flaw just changing coolant. I don't use the green at all anymore, the orange is cheap insurance, nor do I use tap water, @ less than $1 a gallon, distilled is what is called for and what to use. You don't get all the corrosion if you use the orange, you don't get the mineral deposits if you use distilled water. I can't change what my stuff has endured until I got it, but can stop it here. Radiators are so cheap now usually $75-100, I'd not fuss too much over that.

raski

Trapped air is only an issue if the air is trapped behind the thermostat not the upper hose end. The stat will never open if hot coolant is blocked by an air pocket on the pellet side.. Once the stat opens, coolant will rush thru the upper hose even if air is trapped there and get belched out into the coolant bottle.. If your stat has a jiggle valve, trapped air will pass thru that. I always drill a 1/16 inch hole in the flange of the thermostat if there isn't one to prevent any air pockets from collecting there.