Recurring air in cooling system

[BarryK]

Hi all,

I have had recurring problems with a gurgling sound in heater core and poor heat which I solved by bleeding the air from the cooling system. I used a tall funnel with the truck parked on a hill to get the radiator higher than the engine, left engine running as I added coolant. Heat improved and noise went away.

I have done this twice and the noise is back again. The coolant level slowly drops but I don't know exactly where the leak is. The carpet is dry in the interior, so the heater core should be intact. No coolant on the ground under engine. Maybe some minimal coolant staining behind the water pump, near the junction of the intake manifold an passenger side head.

The engine oil looks clean, no definite glycol contamination:
AGCO Automotive Repair Service - Baton Rouge, LA - Detailed Auto Topics - Coolant in engine oil

Is a head gasket leak a possibility? How would you troubleshoot this problem?

Truck has about 112,000 miles.

Thanks!
Barry

1998 Quad Cab

 

[rowdyram]

A head gasket is possible but given your milage I'd say far from probable. Does it overheat?
I'd start by checking the radiator header plates and all hoses then to the timing cover and water pump then to the intake checking them all very closely

Tip: if you warm it up fully when the coolant is topped off(15 miles or so) then shut it off and wait about 5 minutes the cooling system will build the most pressure and a leak will usually show up at this point.
Or you can buy a pressure tester

 

[Leftlane]

I agree the rad is the most likely culprit, look at it closely with a flashlight.

 

[Arlucian]

Also look for something that looks like salt scale/ dried coolant around your hoses, you don't have any drips but it doesn't mean you dont have leaks sometimes they are minute or only come around maybe on the highway etc.

 

[Merc225hp]

Coolant going down/lost/burnt slow is a telltale sign of cracked heads. If no leaks are found that is.

 

[BarryK]

Thanks all for the help!

No the engine does not overheat. I will check for leaks carefully and maybe have it pressure tested!

 

[Merc225hp]

If the heads are cracked like I think they are, the psi test may or may not show it. Good luck and keep us up to date. Oh yes the heads crack between the valve seats so not visible from the outside of the head.

 

[BarryK]

I checked the engine bay after the engine was warm, after about 5 min cool down. (Thanks for that tip!) I found a line of coolant along the junction between the timing chain cover and the engine block, passenger side. No other visible leaks.

Can air also get into the system from here, rather than pulling coolant in from the overflow tank?

 

[rowdyram]

Glad to hear you found it. I'd suggest a timing chain and tensioner while your in there.

And yes it will pull air in.
When it heat soaks after shut down the pressure bleeds out before it cools then when it dies cool it won't pull enough vacuum because you lost volume in the system and what vac it dies pull sucks the air in.

 

[Arlucian]

Glad to hear you found it. I'd suggest a timing chain and tensioner while your in there.

And yes it will pull air in.
When it heat soaks after shut down the pressure bleeds out before it cools then when it dies cool it won't pull enough vacuum because you lost volume in the system and what vac it dies pull sucks the air in.

At the very least check the deflection and see if your close to going out of spec so you dont get a nasty surprise later on.

 

[BarryK]

Thanks all again for the help!

Barry

 

[DAN 25]

I am fixing the very same issue in my 1994. I kept developing leaks around the thermostat housing. Replaced gasket several times. This fix is a pain because you have to strip the front of the motor. Be sure to test the thermostat before you install it. I got a new water neck or thermostat housing NAPA 605-170 which is fairly thick cast aluminum made by Balkamp. Checked it with engineers square and it is dead flat. Strongly suggest you replace the bypass hose $6 while you are at it.