Slow Coolant Leak....Odd Pressure Test Results

Maintenance/Repairs
1

Good evening, new to this forum and have an odd issue:

2006 Malibu…86k miles…4cyl…bought in 2012 with only 7k miles (bought it at auction)…only things done since purchase are rear calipers / disks and replaced tires…

So I was surprised when 2-3 weeks ago I received a low coolant message…figured that there must have been a minute amount of coolant leaking over time so I just put 1-2 cups of dexcool in the tank…then yesterday I saw another low coolant message…worried now I added another 1-2 cups…now overheating issues or indicators…no visible leaks or fluid under car…

Tonight I did a pressure test with a kit I bought when my old Jeep had a head gasket issue that I suspected and confirmed…

Tests:
1-Cold Pressure Test: Applied tester to the overflow tank and put in 10psi…held…no leaks
2-Cap test: Applied tester to the 15psi cap…pressurized…around 17-19 psi the cap would allow air to escape…allowing for a margin of error that sounds fine…
3-Warm Engine Test: Applied tester to the tank…no sudden rise in pressure…which is supposed to be expect to rise to 7psi-ish if all is right…doesn’t rise past zero for 15min and car gauge shows that it is now a warm engine…what gives?..any ideas?..why is the pressure not rising?

Looked at exhaust and there is vapor coming out…not a lot…but you can see exhaust when the engine is warm…but then again it is 45degrees out right now here in Virginia and maybe it’s just engine exhaust and the natural water vapor that comes from the chemical reaction of gasoline combustion…nothing like the mass of white smoke when my Jeep’s head gasket blew…

2

You have a head gasket that is leaking only when the engine is at operating temp. I had one like that on a 61 Mopar 318 poly head engine, Didn’t find any breach in the factory stamped steel head gaskets , but replacing them with aftermarket composition gaskets stopped the leak.

That is I hope you have a head gasket leak and not a cracked head or block. Might be a good time to learn to do a head gasket while you have a 4 cylinder.

I would confirm it with a chemical test kit you can get at a perts store. Don’t test coolant you have just added, if necessary draw some from the bottom of the radiator.

3

at 45 degrees outside, 15 minutes may not be long enough, are both upper and lower radiator hoses hot?

4

Yes could be head gasket but are you sure you are losing coolant? If you are then it has to be going someplace but have you ever changed the Dexcool? It’s long over due.

The other thing is if you are not losing coolant, it might just be a bad low coolant sensor, due maybe to bad coolant.