You find coolant in the oil, or bubbles in the overflow tank, or the car starts pushing water out under boost. So you buy a head gasket, do the job properly, torque everything to spec, and three months later it happens again.
That is the point at which most people conclude they got a bad gasket. They did not. They fixed the symptom.
The actual cause: the open deck
The 4B11T block is aluminum and open-deck. The cylinder liners stand up from the block without being tied into the outer wall at the top. There is a coolant passage where a bridge of metal would be on a closed-deck engine.
Under normal factory boost this is fine. Under 400, 500, 600 whp of cylinder pressure, the tops of those liners flex. Not much - we are talking thousandths - but the head gasket is being asked to seal a joint that is physically moving every combustion cycle.
No gasket seals a moving joint. That is the whole story.
Why the factory bolts make it worse
Mitsubishi used torque-to-yield head bolts. They are stretched permanently on install, they are single-use, and the clamping load they provide was calculated for a factory-boost engine.
They are not holding the head down hard enough against modern cylinder pressures, and every combustion event that lifts the head a fraction lets a little combustion gas past the fire ring. Once that starts, the gasket is being eroded, and failure is a matter of time.
The fix, in order of severity
Step 1: Head studs. Always.
ARP CA625+ head studs are the single highest-value part on this list. CA625+ is the strongest material ARP makes. They clamp the head down properly, they are reusable, and they cost a fraction of the engine they are protecting.
If you are running any meaningful boost on a 4B11T and you do not have head studs, that is the next thing you buy. Not a downpipe. Not a bigger intercooler. Studs.
Step 2: The right gasket
A Cometic MLS head gasket in the correct bore and thickness for your build. Thickness matters - it sets your compression ratio and your quench. Do not guess it, and do not just buy whatever is in stock.
Step 3: Main studs
ARP main studs. People skip these because the failure is at the top of the engine, so they think about the top of the engine. But the block is aluminum, it is being clamped from both ends, and stabilising the bottom end helps everything above it stay where it should.
Step 4: If it is still lifting, the block is the problem
If you have good studs, a good gasket, a properly prepared surface, and it still lifts, you have not been defeated by parts. You have been told something: the cylinder pressure you are running exceeds what an open-deck block will hold, full stop.
At that point the answer is not another gasket. It is Darton sleeves, which convert the block to a closed deck and tie the liners together. That is a machine shop job and a different budget, and we cover when it is justified in sleeved vs unsleeved.
Things that are not the fix
- Retorquing the factory bolts. They are torque-to-yield. They are already stretched. Retorquing does not restore clamp load.
- A thicker gasket. It will not fix a moving deck, and it drops your compression and hurts spool.
- Turning the boost down and hoping. This works, and it is a legitimate choice, but be honest that it is a retreat rather than a repair.
- Copper spray and a prayer. No.
Do it once
The head is off. Whatever you were going to skip because it was a few hundred dollars more - the studs, the right gasket, the valve stem seals, the timing chain - it will cost you five times as much to go back in for it later.
While you are in there: valve stem seals are the cheapest part of the job, and an OEM timing chain kit is far easier now than after it stretches.
Talk to us before you order
Tell us your power target, your fuel, and what already failed. We will tell you what actually needs to happen - including when the answer is that studs and a gasket will genuinely be enough and you can stop reading forums at 1am.