A while back I had the dealer do an oil change and upon inspection noticed my water pump was leaking slightly so I had them change it while they had it. That was at the beginning of spring.

truck ran a few degrees warmer than usual, just a bit over mid gauge around 220 but I didn’t worry about it too much. Winter came and I noticed my heater not working properly so I did a flush and fill making sure to vacuum down the system and do a negative pressure fill to get any air out. Got the heater working but never as hot as before the pump change.

Now the heater barely works. All doors and actuators are fine. Truck does hit 3/4 on the temp gauge regularly but hasn’t gotten above 240 consistently. It does get hot enough to push coolant out of the radiator into the overflow reservoir and sometimes I see leaking when the reservoir overfills.

Dealer said the pump is fine but did a coolant test and claims I have a blown head gasket causing all the issues. For the last two years I have been chasing this problem.

Compression test and cylinder leak down test are fine. I did change the radiator due to a small end cap leak last year and have done a few pressure tests which are good.

Water pump is not leaking or making any abnormal noise that I can tell but still have the same heater / running hot issue.

 

Do your own test of the coolant for combustion gases. You can get the kit at your local auto parts store.

Usually, poor heater performance (everything else actually working properly) indicates low coolant......

And on that note, are you losing any coolant? Do you have to add some regularly?

 

I’ve done all the tests myself as well. First coolant test I did failed. Had to replace both exhaust manifolds due to cracks and broken bolts causing a really bad leak and since then two coolant tests passed. I’ve pulled the spark plugs as well and they show no signs of water fouling, just the normal brown color. I also pressurized the coolant system and scooped the cylinders with an inspection camera to check for seepage and saw nothing. Pressure test of the coolant system shows no leaks either since replacing the radiator.

I do add coolant but not constantly. Prior to this post it has been almost a year and it’s almost always equal to what’s in the overflow tank when I do.

the only tests I haven’t done is check pressure in the heater hose outlet at the water pump and I’ll be doing that soon.

I’ve had a few cars with blown head gaskets over the years and not one ever lost cabin heater function.