Could be partially clogged. Might try flushing it out.

 

Would it being plugged cause enough cavitation to cause the gurgling noise in it?

 

It is possible. Does the heater put out really hot air like it should?

 

Yes the heater works fine, seemed to anyways all winter. Had an issue last november with the truck not coming up to operating temp so I changed the thermostat and that cured that problem. This gurgling noise did not start though until fairly recently, roughly about a month or so ago.

 

Very strange indeed.

 

Okay heres an update:

Problem goes away when the heater lines are pinched off. I let it sit and run in the driveway the other night for a good 45 min with the rad cap off, driveway is at a fairly good angle as well. Lost a bit of coolant but kept it topped up. Started it up the next morning and it seemed fine all that day. Next day comes around and same issue again, flushing noise when its first started, then as it warms up it goes away slightly. It will follow the rpm of the motor up to a certain extent then it will stop at hwy speed (roughly anywhere above 60km/h)

I put some of the leak detection dye into it today and will drive it for a few days then look with a uv light to see if I can see anything and post back... Lol really starting to bug me!

 

Tested the truck last night with the blacklight in the shop, looked at the tailpipes, exhaust manifolds, oil dipstick and the engine oil fill cap... Found nothing, no trace of the dye at all. Im Stumped! If it was air ingress from a leaking head gasket there should be some sort of dye somewhere in the motor would there not be? Either in the oil or on the exhaust side somewhere? I know the problem lays in the cooling system/heater core because I pinched the heater hoses off with a set of line pliers and the noise went away instantly.

Went out today and started the truck,Its the worst when you first start the truck up when its cold, its like a "rush" of coolant to fill the heater core up, the noise follow the engine rpm up until about 1200 or 1300 then the noise goes away. Its like the water pump cant supply enough coolant for the heater core at an idle. When the trucks warmed up and you pull up to a light and let it back down to idle you will get the flowing coolant noise again, but not near as bad as when the trucks cold. This makes no sense to me at all, I bled it the other night with the rad cap off for a good 45 min that should have gotten any air in the cooling system out should it not have?

Is there any other way to bleed the cooling system? This is getting very annoying, start the truck up and it sounds like a god dam waterfall inside!

 

Did you check the ductwork for dye?

Perhaps your waterpump impeller is worn and not pushing coolant properly.

 

Water pump sounds like a possibility. The 4.7 has a bleed plug on top of the motor where the upper hose connects. When i flushed my heater core recently i did not have any problems bleeding air out of the system, so i don't see how you could have air in the heater core constantly, mine just flushed itself. Check to see that you have coolant constantly flowing. When i opened the radiator cap, there was always a little stream of coolant flowing from the small hose into the reservoir.

 

Checked the ductwork quickly for any dye and didnt see any... The antifreeze is topped up to the proper level in the rad and overflow tank. I checked this the other day and made 100% sure both were up to the proper level just so I could have a reference point.

I dont know why there would be air in there either, it doesnt make any sense that it would show up within the last month or so with this noise when no work has been done on the truck at all. Like I said before I changed the thermostat early last fall so if was air in the system to me it should have done this the entire time and not just started.

Is it possible that the water pump is worn enough that it will cavitate the coolant but still keep the engine at operating temp and not let it overheat?