Fuel in Oil

96 4wd 2.7l tacoma

Bought it 4 years ago with a blown head gasket and a cracked exhaust. Drove it in such condition until it didn't start this morning. Spent a few hours tearing it down to the crank case from the top side. Cylinder 3 is the problem cylinder...was leaking water to the outside yesterday, and the engine lost all compression today instead of just having weak compression.

Figure while I'm replacing the head gasket and exhaust manifold, I'd look into the cause of fuel getting into the oil at a pretty abnormal rate. In 20 years of wrenching I've only ever dealt with excess fuel in the oil on diesels. Not sure what to look at on a gas engine. Common sense tells me to clean and test the injectors for proper open/close; is there anything else specific to this engine, or gas engines in general, I should prioritize to check for the cause?

regarding the rings, willing to open up the crank case and remove the pistons if absolutely needed, but wondering if pouring some low viscosity oil on top and taking precision (accurate to 1/10000th in) depth measurements an hour apart would be sufficient?

 

I'd suspect a leaking injector.
I guess a no spark situation could cause the fuel issue too.
But I'd think you know if you were running on 3 cylinder.
As for rings, I'd do a compression test on cylinders 1, 2, and 4.
That should give you a general idea of the rings.

 

I went into the teardown a little zealously having seen the water leaking from between the jead and block yesterday so I've already got the engine torn down to the block. After I get the head back on I'll do a leakdown test before complete reassembly since the valves are still fully seated. Definitely going to clean and test the injectors, though, and replacing all the plugs. Cylinder 3's plug is going to need a helicoil...the old plug was definitely crossthreaded into the head and looked to be burned away. I'm thinking at some point before I came to owning it, plugs were changed, it got cross threaded, and when they were next due only the other 3 were changed and cylinder 3 went dead, leading to a chain of failures to follow.

But yes, the engine has been running on just 3 cylinders the last 4 years...probably much longer.

 

Tn is right on point

the only way fuel can mix with oil
(aside from an idiot owner pouring gasoline into oil fill)
Is in combustion chamber
Worn rings and/or failed injector(s)

as you confirmed, #3 is an issue
Most likely combo of both

 

If you drove with #3 being dead, you might have washed out the cylinder with the fuel.
Fuel is not a good lubricant, it won't protect the rings and bore like oil.
See if you can tell a difference in the cylinder bore color and "texture" compared to the other cylinders.
If it's washed out, you need to hone it at a minimum. You need crosshatch to retain oil.

 

Thank you for that tip. I'm picking up parts in the morning, so I'll check the surface before heading to get them in case I need new rings and/or sleeve for #3.

 

Quite impressive that the motor ran on 3 cylinders for 4 years