Got an 09 equinox with 3.4 to fix head gaskets. Seller said shop did coolant test and it failed for hydrocarbons. It is using coolant but has no overheating issues. Yet. Been driving it for several weeks. Runs fine. It had a stored code for cyl misfire but nothing current. Any chance it’s bad intake gasket and not head gasket? Could a leaky intake somehow give a positive hydrocarbon result?
No, a leaky intake gasket would not throw a hydrocarbon positive… Why not?
The intake pressure goes from 0 to a vacuum of about 20 inches of mercury (or -9 psi). The cooling system goes from zero to about 15 psi positive pressure. The intake pressure is never higher than the cooling system pressure so no hydrocarbons shall pass into the cooling system.
The combustion chamber pressure is higher than the coolant pressure for most of 2 of its 4 cycles and lower for most of 2… So coolant goes into the cylinders during intake and exhaust strokes and hydrocarbons goes into the cooling system during compression and power strokes.
You have a bad head gasket!
I’d check the transmission fluid level, though. If the trans cooler in the radiator fails, coolant will fill up the transmission so the dipstick will show over-full. And trans fluid will migrate into the coolant so you’ll be able to see an oil slick on top of a coolant sample. But you won’t register a fail on the hydrocarbon test. I just had that issue on my truck.
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If your coolant loss is less than a cup a week, I’d suggest that you put a bottle of Subaru Cooling System Conditioner into our system. You can get it at any Subaru dealer or off Amazon but you have to be quick. This stuff only works during a very narrow window of opportunity. You have to get it in there before you start losing a lot of coolant.
It is not one of those miracle head gasket repairs that not only do NOT work but will do serious damage to your engine in the process. I have used this in two engines and both are going strong, one of them is now going on ten years, the other about 7. However my son used one of those miracle cures and now we are about 2 grand into repairing the damage it did. Well some of that damage is actually a few upgrades but still it needed to have the head completely rebuilt, a new radiator and all the coolant passages in the block needed cleaning by hand.
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