ok my girlfriends 4.7 keeps on overheating. Replaced the thermostat, though it was fixed but started doing it again. Then I found a massive air lock in the upper coolant hose, so I bled it.... Good for a few weeks then the air lock came back.... Bled it, replaced radiator cap, sealed the bleeder screw up good, good for a month or so and now it just did it again. Anyone have any idea where the air lock is coming from or where the coolant could be going??? Help!
If bleeding was done properly shouldn't develop air as closed system. Usually, I remove the bleeder plug, fill with antifreeze through radiator, then actually top off through the plug hole, then replace the plug.
Hydraulic fan working properly?
I would try a pressure tested when the engine is cold to see how the coolant is escaping.
Thats how i bleed it also... I used sealer on threads too but it continues to be an issue. Are there any common coolant issues with the 4.7? I really hope its not a head gasket or something serious, the oil looks clean but in the top of the oil filler neck there is some white/yellow cheese creamy ****.....
None that I know of, but I'd certainly do a pressure check on the cooling system. Could be a slight leak that is not seen under the Jeep, or evaporates quickly. On our '01 the rad core rotted out in the lower front. The air dam attached to the rad is a great idea to deflect incoming air through the rad, but as it extends up maybe 1/2" debris accumulated and contued to remain damp and the core was a goner.
That hydraulic fan is pretty neat, not that it will stop overheating if low on coolant, but it will certainly provide enough air movement to keep the temps down in the hottest conditions.
If the hydraulic/mechanical fans are working correctly and you still experience overheating after replacing the thermostat, my bet is the radiator has gone bad (especially if it is still the original). I replaced most of my cooling system components over a 2 year period chasing overheating. Problem got worst over time. Finally replaced the radiator and all was well.
I have found the easiest way to bleed the system is fill it up until fluid runs out the bleed plug. Close the plug, put the pressure cap back on, warm it up a bit (maybe 150 or so, but not full operating temps), shut the engine down, and then very slowly lossen the bleed plug just enough for any remaining pressurized air or fluid to come out. Then reseat the bleed plug, cool engine down, top off anything needed in the radiator and overflow tank. Then drive around to get engine to normal operating temps. Do this for a couple of days and it should naturally remove any residual air through the overflow tank after a few cycles. Check overflow after a few cycles and top off as necessary.
I am curious -- how did you find a massive air lock in the upper coolant hose?
Y2K WJ 4.7
Last edited by txtumbleweed; 01-06-2009 at 09:34 PM..
overflow tank level stays the same all the time......... havent done the pressure test yet.
My Stant tester has paid for itself 1000 times. Anytime someone is loosing coolant, let the vehicle cool, install the tester and pump it up to 18/20 lbs depending on the cooling system, and let it sit. It may take time, but you'll find the leak.