In reply to codrus (Forum Supporter) :
I've ran the tests. My problem is, this is the first major engine issue I've attempted to diagnose and don't know how to interpret the data.
To put everything in one spot:
Compression test:
Engine hot
1- 180
2- 180
3- 180
4- 180
5- 160
6- 100
Leak down tests:
Engine cold
1- 90/74
2- 90/78
3- 90/85
4- 90/86
5- 90/80
6- 90/40
---------
1- 90/81
2- 90/87
3- 90/86
4- 90/87
5- 90/73
6- 90/52
On all cylinders you could hear air at the oil fill. Wasn't particularly loud, I had to put my ear all the way to the hole. Cylinder 1 was louder than the other 5. I felt a little air at the dip stick, if I covered the hole with a finger it felt like there was pressure. Not much though. I never heard anything at the exhaust. I held the back of my hand up the exhaust, cylinders 5 and 6 felt like there was a little bit of air coming out of them. Not very scientific, but it smelled like there was something coming out. I really couldn't see into the expansion tank since I had it to move it way up out of the way to spin the crank, but I didn't hear anything and I don't know if I would have been any to feel them, but I didn't feel any bubbles when I touched it. I took the air filter off, didn't hear anything at the throttle body.
I don't know if hearing air is normal or if you aren't supposed to hear anything. The air has to go somewhere right? When reading online about leak downs, I'm reading you are listening for a whistle. I heard the opposite of that, something like a small amount of air moving in an confined space. The noise was the same across all cylinders, it was slightly louder while testing cylinder 1, which is the closest cylinder to the oil fill. I never heard anything at the dip stick. I felt the slightest bit of pressure when I covered the dip stick hole with my finger. But, maybe that was imagined since wouldn't the air go thru the oil fill before making it all the way down then up the dip stick tube?
I pressurized the cooling system to 15psi. Within a 5 or so minutes it had dropped to 14psi. I was able to check it today, roughly 24 hours later, and it was at 13psi. I assume this means a slight leak.
https://imgur.com/a/ixMK2vm
I bore scoped the cylinders. I didn't do a great job. I was the first time using this camera and I was trying to beat a hurricane. To me, I didn't see anything on the cylinders that wasn't normal. I didn't see any discolorations or gouges. All cylinders had cross hatching. The carbon on the pistons all looked really similar except 5 and 6. The carbon in those cylinders looked darker and shinier.
The low compression on adjacent cylinders, the slight coolant leak, the pistons in the cylinders with low compression looking wet, and the fact these engines seem to be pretty bulletproof other than overheating and head gaskets make think it's the head gasket. But like I said, this is my first time muddling thru diagnosing an engine.
It is a high mileage engine so I'm not ruling out blowby. I am curious what some of you are seeing that makes you think it's blowby over a head gasket. Would an oil analyze detect blowby? I've never gotten reports of gas or coolant for that matter in the oil. The car doesn't smoke. Burned half a quart of oil in 4 hours of track time. I added a picture of the spark plugs to the imgur link.
Is a definitive answer possible without completely taking things apart, or is it always going to end up being "it's most likely this but it could totally be this?"
