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FYI on oil in coolant

My wife has a 2005 Equinox and we discovered an oil residue in the coolant pressure tank. I wanted to diagnose the problem myself and hopefully rule out a blown head gasket. I flushed the system and replaced the hoses that had began to break down. I dove the car for a while and let it sit overnight. Sure enough the oil came back. This time it was blackish put couldn’t really tell. The 3400 engine in the Equinox has no pressure on the top of the engine while running so transmission cooler must be the culprit. I ordered a new radiator and the broke one sat in the shop over the weekend and while it was there it drained. The milky fluid leaked out and separated from the coolant. I then knew it was trans fluid because it was red after separating. Changed the radiator and the problem is fixed. One thing I did learn is head gasket doesn’t mean engine killer. Just labor intensive.

You’re lucky since that engine is notorious for blowing head gaskets.

U see Cadillacs with oil/coolant issue and folks always assume it is typical north star head gasket issue. Fact is, it’s failed radiator. U can pic these cars up fairly cheap due to the misdiagnose. But it’s only temporary. The heads will let go eventually. Such is the fate of north star motors.

I’ve read that the aluminum Northstar engines are prone to have a cracked block

What I mean is, you pull the head, then you find that the block is cracked, right around the female threads for the head bolts

I’ve got about 204K on my Olds Northstar engine and no problem yet, but I would never fix it.

The Olds version Northstar had a reduced bore and displacement (4.0L) which provided enough surface area to get a good head gasket seal. It allowed bigger studs to be used to secure the heads to the block…These engines, by the way, were originally designed by Lotus as a racing engine. GM bought Lotus and in desperation to meet C.A.F.E. fuel mileage standards used the design to compete with the European luxury cars which offered advanced engine designs…In the end, Cadillac went back to using Chevy Small Blocks, push-rods and all…(With great success…)

Well that’s good to hear. It seems like its been a good little engine but just hard to work on. About two hours for a belt change, forget the water pump, cleaning the EGR passages requires pulling the trans so the light still comes on, etc. Doesn’t go anywhere much anymore anyway. It does have the autobahn package so have no idea how fast it would go ungoverned.