Oil on spark plug threads
TECH Senior Member
Joined: Jul 2009
Posts: 8,032
Likes: 661
Put air in the cylinders with the valves closed and listen at the tailpipes for air. I would barrow a compressor with at least 125 PSi. This is typically the highest the bargain compressors can go. IF you get a better compressor, I'd recheck the compression/leakdown.
Do you have ported heads? Most head porting removes the bump in the intake port under the rocker arm bolt. This allows oil to migrate down the bolt threads and into the intake port and is carried into the combustion chamber. I have had this problem in the past. If you find this use a good thread sealer on the rocker arm bolts and it will stop this oil path into the engine.
MrE
MrE
Well I finally got around to working on the car again. I changed the valve seals on the 3 bad cylinders yesterday. I also put blue loctite on the rocker arm bolt threads and some RTV under the bolt heads. I let the thread sealant cure over night and ran the car today. I let it run for 5-10 minutes and get up to operating temperature. The 3 bad cylinders still have some oil on the threads and the tip is still a little wet. The picture below is 1 of the bad plugs. I'm not sure what else I can do to stop this from happening.
A guy at work has a Denali w/ a 5.3 in it. He asked me to look at an oil leak tonight and on #7 cylinder there is oil coming from the spark plug hole. It's running down the block. It's not the OPSU or valve covers. The oil basically looks like a triangle with the spark plug being at the top point. My best guess at the time is the valve seals are leaking and the oil has works it way up the threads. Now I think about it I need to tell him to make sure that plug is tight.
I think the crappy PCV system has a lot to do with it.
How else can oil get in there besides:
Ported heads with rocker bolts exposed and no sealant on rocker bolts
Bad piston rings
Bad valve seals
Porous head casting
How else can oil get in there besides:
Ported heads with rocker bolts exposed and no sealant on rocker bolts
Bad piston rings
Bad valve seals
Porous head casting
TECH Regular
Joined: Sep 2008
Posts: 425
Likes: 1
From: Scottsdale, Arizona
Only use copper anti-seize on spark plug threads. Reason being is that the copper has better grounding abilities that silver anti-seize. I've had changed plugs on my race car one time and all I had was silver, it slowed the car down. After I cleaned up all of the mess, and changed over to copper, the car came back to normal. It still had some oily type residue on the threads after changing them again.
Never use oil! You need the plugs to ground properly
Never use oil! You need the plugs to ground properly
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What Mark 200 said^^^^^^
Take the intake off, and have a look at the back of the valves.....
You stated that the engine is "fresh". Does that include the heads?
Changing seals on a valve w/ excessive stem clearance, is of little value.
Take the intake off, and have a look at the back of the valves.....
You stated that the engine is "fresh". Does that include the heads?
Changing seals on a valve w/ excessive stem clearance, is of little value.
This crap won't happen to me. Assuming your heads oil control is proper another big source of oil migrating to combustion chamber is low tension oil rings in a performance engine that's one, another is ring gap, excessive gap will cause extra oil to reach the combustion chamber common with nitrous builds or overlooked excess gap left in some pistons and not in others.
This is some of the reasons I build my own engines and don't trust anybody to do my s--t.
I always only use high tension oil control rings in my performance engines, cause I HATE oily spark plugs and my ring end gap deserve a full day of my attention, so I do it by hand and take my time, the result is always the same,
exactly the same color on every plug and looks like the stock engines plugs.
This is some of the reasons I build my own engines and don't trust anybody to do my s--t.
I always only use high tension oil control rings in my performance engines, cause I HATE oily spark plugs and my ring end gap deserve a full day of my attention, so I do it by hand and take my time, the result is always the same,
exactly the same color on every plug and looks like the stock engines plugs.
