So I've been putting off trying to figure out poor heat and some coolant loss that happening with my grand Cherokee. It's a 2007 with the 5.7 Hemi. I replace the water pump and thermostat about 18 months ago, using gates parts and it had great heat last winter, but this winter it has been marginal at best. Heater doors and motors are all working and moving as the should.
I've flushed the heater core with the garden hose in both directions, top off and burped the system and seemed to have better heat for 1 or 2 tanks of gas. Gradually the heat returned to not working well, but if I was to run the fine up to 2500-3000 rpm's for about 3-5 minutes the heat would improve for a while. The engine operating temp stayed around 201-207 with a 203 degree thermostat but the heat has never felt "hot". Both heater hoses are just as hot as the upper radiator hose when warmed up.
Since flushing the heater core and getting the coolant level stabilized, I've notice it gradually using some coolant. It's gone from "full" to about 3/4" below add in the reservoir when cold over the course of about 500 miles (if that).
I was thinking the coolant loads might be a head gasket starting to seep, and maybe air was getting trapped in the heater core leading to poor heat ( even when working better, the floor outlets are warm, but defrost and dash vents are cold).
I used a combustion gas tester today and let the gone warm while using a turkey basket to lower the coolant level in the radiator a couple inches. Once the engine reaches operating temperature I put the tester in the radiator and let the engine idle for another 5-10 minute then used the bulb to draw air through the liquid until it wouldn't draw anymore. The liquid stayed blue, and to make sure the liquid was good, I held the tester near the exhaust tip and drew air through the liquid and it turned yellow, so it seems to pass.
I let the jeep sit for about 4 hours and retested to see if hear cycling changed anything. I installed the tester and fired up the engine. There were bubbles coming through the tester for about 5 minutes, but no color change. I waited until the engine reached operating temp, then proceeded to bring up the rpm's up to 3000 and held it steady for a few minutes, more bubbles, but still blue. So I though, maybe it needs to be under a load for the gasket to seep and put it in drive, held the brake, and brought the rpm's up to 2000-2500 for a minute or two.
It was after being placed under a load that there was suddenly a plume of yellow in the tester and then is starter squirting coolant everywhere. Once it stopped pushing out coolant I let it idle and it seems to have gotten rid of whatever was causing it to erupt. I left it idling and cleaned the tester.
After I cleaned the tester and went back out to the driveway I repeated the previous, with similar results. The different was once the engine stopped pushing coolant out the tester, I took the tester out and started cleaning up, only to witness the engine start pushing more coolant out of the radiator.
So anyone have experience with combustion gas testing giving a negative result, with a bad head gasket, or other ideas?
Im going to get a new thermostat from the dealer, top off and burp the cooling system and see if that helps. I also plan to return the combustion gas tester and get the cooling system pressure tester to see if it hold pressure, and how quickly it builds pressure.
If I can rule out a head gasket then I don't mind digging deeper Into the heater issue, but I'd hate to spend more time and money on it if I need to pull the heads, since I don't know what I'll find (bad gasket, cracked head, etc).
