Hello everyone,
My '06 4.2 with 100K miles is having some issues. I don't drive it much now days, but I had it out the other day and I noticed that the heater started getting cold. When I started heading home, the truck started to heat, but never did fully overheat. I got home and saw that the coolant was low.
Today, I put 1.5 gallons of coolant in it to bring it to the cold fill line, and started it with the cap off. The heater started to get warm, and as the truck started approaching operating temperature, the heater turned cool. I could hold the truck at about 3K rpm and the heater would get hot. After going back to idle, the heater would get cool again. The drivers side heater hose is warm, but the passenger side is not.
When the thermostat opened (I assume this caused it), the truck pushed a bunch of coolant out the opened tank. Then it settled down. The heater was still not hot though, and only one warm hose.

It seems like I might have a few issues...Heater core stopped up, maybe a water pump issue? I'm not sure why it pushed out the fluid, and I don't know how it got 1.5 gallons low. I don't see any external leaks, which really concerns me. The oil looks fine

 

the heater hoses route over the top of the motor and down to the heater core. It is not uncommon to trap air in the heater core... as you said, when you rev the motor it tends to push MORE water and some gets into the core.


a bigger problem is the coolant level. If it is not on the ground then it is either burnt or in the oil pan. Make sure there is not coolant in the oil pan. If none, then you have a head gasket failure or crack letting the coolant into the combustion chamber.


You can cut one of the heater hoses and splice in a TEE and use the third leg as a flush for the garden hose, and also a vent when you fill the coolant.. Get everything full and then confirm that you have heat... then look for leaks.... then determine how fast you are loosing coolant... then decide if you want to try a SEALER or time to pull the heads.

 

I fired it back up yesterday and it didn't push the fluid back out and had fairly consistent heat. The heat got cool right before the thermostat opened up. So, maybe that issue is an air bubble.

The low coolant does worry me the most. I would say it has to be burning it because the oil is fine. I do not see any bubbles in the recovery tank.
I just replaced a blown head gasket on my 5.4 with only 125K on it. I sure hope this one doesn't need one at 100K. I never knew head gaskets were such an issue!

 

If your using a gallon a week, that's a problem... IF it went down the last few months, then I would determine "HOW FAST" and if its a small leak, try the BARS LEAK COPPER gasket sealer.. I have used that several times on various cars/ trucks with good success. It mixes with the antifreeze, don't need to drain.

 

A good size leak can also pressurize the coolant tank while running and cause the cap to pop and blow coolant all over....... or it could have overheated due to the low level.. FILL and retest for operation and coolant usage.

 

A bad water pump could cause the problems; if the impeller is corroded badly it will not be able to move the fluid at low RPM. If the seal is also leaking, it will lose coolant as well as not be able to build pressure. I wouldn't just pull the water pump - first verify whether its leaking or not. If not leaking it still could be damaged internally. Much of your problem is caused by an open cooling system so you have to find and fix the leak before you can find any other problems.

 

Thanks for the input guys. I've drove it a couple more times and no overheating or overflow...unfortunately, the missing coolant went somewhere. It might just be a very slow leak and I hadn't noticed. I'll see what happens in the next few days