Head Gasket Blown but Good Compression?

[ECST5]

Been having trouble with my 97 the last couple weeks.

Started as a really rough idle, then I got P0306 misfire on cylinder 6 code. Swapped spark plugs around to test, swapped coil packs around to test, swapped wires around to test, all still returned P0306 code. So tested the injector, resistance was a little high but I figured something else must be wrong with it, so I put a new oem injector in (and new spark plug wires) and… still P0306 code.

When test driving after moving coil packs, car got really hot and was steaming coolant into reservoir. Thought it was just a weird thing from test driving, but it’s started to steam whenever ran. Reservoir also disappeared over night when I refilled it.

After doing injector it started doing weird idle stuff (idling at 1700rpm, surging, idle drops when ac is turned on) and it was still misfiring, I checked compression and boroscoped through the spark plug hole. Compression was 155psi which was the same as other cylinders on the driver side head. Boroscope shows what I think is coolant, but very hard to tell from crappy camera lol, I’ve attached that photo.

So unfortunately seems like a head gasket issue, unless IAC valve is somehow dumping coolant into only cylinder 6? Anybody have any ideas before I rip this head off and get it pressure tested?

Edit: added a second photo showing oil puddle in bottom of intake plenum, that oil appeared in under 10 minutes of running car, seems like a lot of oil for such a short period? That photo is of cylinder 6 intake tube, other ones do not have nearly as much oil.

 

[4flyer]

Could be that the engine is just tired. 155 PSI is pretty low

 

[mtbtim]

Do a leak down test of Cylinder 6 and then you're wondering will be over.

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[Hungryhawk]

I remember wet and dry compression tests help identify piston ring wear. Wet with oil helps seal rings so pressure reads higher. If no change then issue is valves or headgasket.
Test kits check for exhaust gases in coolant and coolant in exhaust.
You can pull #6 plug and put inspection camera/bore scope into cylnder and look for steam cleaning caused by coolant.

 

[thegipper]

As Timmy said, do a leak down test. A leak down test was the only way I was able to 100% confirm my head gasket was blown.

Good luck

 

[BuffaloBass]

or coolant pressure test

Or pump up the coolant system to 25 psi and see if it loses pressure. If I had, no doubt i would have been losing pressure in the intake galley, where the clear traces of coolant leaks were.

Our 99 became a "Stanley Steamer" due to coolant passages in head gasket failing.