It doesn't sound like the head is problem its the bottom end you need rebuilt Your piston rings are bad or the cylinder walls are worn to much and if you had to change your oil so it won't get in the coolant then there is a serious problem going on.

 

I was told by a few people that oil blowby into the coolant isn't uncommon with hard acceleration and a low-viscosity oil. Once I changed it to 10w-30 synthetic I never had this issue repeat itself. No oil present in the coolant at any time either.

And this only started with the used cylinder head with a valve job...

 

You were told wrong. How do you think oil can "blow-by" into the coolant? The oil and coolant are in two different areas of the block and head. Either one or both of these is cracked, the head-to block mating surface is deformed, or the head gasket is bad. Unless one of these conditions is present, the oil and coolant cannot mix. Completely impossible.

Exception: On cars equipped with an oil cooler that uses oil-to-water heat exchange, a failed cooler can allow mixing. Lancers do not have this.


If you are consuming oil, bad valve SEALS are not uncommon on these engines. Not a hard fix. I would definitely try that before pulling the head apart. When I worked at Mitsu, the only time I saw actual valve/seat sealing issues that affected compression was when the moron let the timing belt break and then took it to some hack shop who installed new valves without grinding the proper angle or even lapping them in. A 4g94 that has had a reasonable history of oil changes will not have valve issues on the original parts. These engines are low-powered but extremely long lasting.

 

I'm assuming this is a gasket issue with the lower viscosity oil, that's the only situation I can see it happening without cracks in the block or head. It was a new head gasket installed, and the higher weight oil has solved the issue. If it ever repeats, I'll assume that things weren't torqued properly and will address that situation.


[QUOTE=mcgarvey;10400294]If you are consuming oil, bad valve SEALS are not uncommon on these engines. Not a hard fix. I would definitely try that before pulling the head apart. When I worked at Mitsu, the only time I saw actual valve/seat sealing issues that affected compression was when the moron let the timing belt break and then took it to some hack shop who installed new valves without grinding the proper angle or even lapping them in. A 4g94 that has had a reasonable history of oil changes will not have valve issues on the original parts. These engines are low-powered but extremely long lasting.[/
QUOTE]

This is what I am thinking might be an issue with the consumption, I had an SAE trained mechanic lap and angle the valves, and I'm assuming these probably had a margin of error when done in a home shop instead of a machine shop with micrometers. But like I said, if I keep the car long enough a new head will be on the shopping list. I should have done that to begin with, but was misled with how much I would "save" if I went with a used head. I'll NEVER make that mistake again.

 

I have to agree with mcgarvey I have never heard of or seen in all the cars I have worked on oil mixing with the coolant and being normal. There has always been an issue whether like you said not properly torquing the head bolts, blown hg, etc.