What caused head gasket leak on N/A engine?
 

Heads were last off approximately last October to replace lifters. Starting in maybe December/January, I'd intermittently get smoke from the tailpipes only during cold start. When I was tuning MAFless sometimes the smoke would come out more frequently, but it never smelled sweet. I was having problems with the coolant level maintaining the correct level, so I regularly topped it off because I couldn't tell where it was going.

Dynoed the car on 3/26. It had a power hiccup right at 6500RPM where according to the graph it dropped ~30rwhp, then it recovered. But according to the numerical data, there wasn't any dip. The raw data shows no samples between 6470 and 6690. The last sample was 6950.

During the next week, I was tuning on the interstate, and the car seemed to hesitate a bit the one time I was between 6K and 7K. I smelled coolant, but my engine temp didn't fluctuate so I drove it home. I found coolant had burped up from somewhere (now I figure from the overflow). Checked the overflow level and it was right at hot.

So on 4/2, I passed using high RPM's and then I started smelling coolant and a smoky haze developed behind me. Long story short, we found a head gasket leak by cylinder 7, and warped 4-5/1000's. The other bank had a valve guide drop, moving in sync with the stem.

So why did it not spew on the dyno, then twice in the next week? I was using the in-car wideband, with a new calibrated sensor. Air pockets in the cooling system? :confused: