unburned oil on spark plugs

D

Duffy1

Well-known member
My new spark plugs burn a dark gray and have unburned oil around the base of the plug . Engine runs good ,does not smoke and uses no oil .The oil level is in the middle of the F on the dip stick. I replaced the head gasket 1500 miles ago and everything looked good . No excessive carbon on the pistons , minimal ring ridge on cylinder walls, etc . This is a B engine , 60 over , inserts on rods only and was rebuilt about 5,000 miles ago . Only thing I can think off that would causes this would be that the oil level is to high splashing more oil up on the cylinder walls than the oil rings can hold back .Anyone have any idea why this oil is on the base of the plugs. Appreciate your responses.
 
could be several things, rings, valve guides, loose pistons, but i would try a hotter plug, one or two ranges hotter or even plugs with a little longer reach into the combustion chamber
 
What plugs are you running? A 3X plug has the tip (end of plug) closer into the combustion chamber than most others that are offered for the A.
 
Thanks for the response fellows .So you do not think the oil level is the cause ? Then of all the sources ford3 listed , valve guides ,in my case sounds like a candidate for the source of the oil getting into the cylinders. On an OHV engine I understand how oil can ,once it gets past the valve seal ,travel down the valve ,if the valve guides are worn . How does this work on non pressurized flat head engines .
 
The grey indicates the heat dispersion of the plug is within range to keep it from carbon fouling. Do not go to a hotter plug. That would make the center electrode and insulator run hotter, but would have no effect on the plug shell.

The oil deposits around the base indicate the engine head temperature itself is somewhat low. Are you running a thermostat? Unburned oil vapor condensation around the plug base is fairly common in low compression flatheads that run cold.
 
My A and B engines that I swap out both get a little engine oil around the base of the plugs especially #'s 1 and 2. They run great otherwise so I just wipe it off. I do think my gaskets are a little squished though. Never thought about vapor though.
 
MikeK and PeterJ ;

Thanks for the response . I am not running a thermostate and in the winter the temperature stays at about 140 so Mikek I think you have solved the mystery . This summer the temp . will be up to 195 . I will pull the plugs then and see how they look at that time . I have had this model A for one year and continue to climb the learning curve with the help of folks on the the ford barn .
 
When you say the base of the plug,do you mean the part of the plug in the combustion chamber? Or,around the base of the plug where it meets the head on the outside.On the outside you will find it is not oil,it is seepage from combustion by products creeping by the threads.After 80 years of overtightening the plugs and stretching the threads,running them too loose,or rust pitting from sitting water,damage from cross-threading,damage from twisting out carbon packed plugs,it can be hard to seal them up tight sometimes.I have one car that makes little rings of oil around every plug with use.It is just sap.If it is on the inside I would tend to think it is formed when you slow down after a nice drive,letting it idle,shutting it off,leaving a little unburned fuel and around the plug.All modern cars operate perfectly at all speed ranges now,with perfect amounts of fuel delivery at all RPM's. Back then things were engineered to give the best performance overall within the price/production/gas quality constraints.Give a little on the high end running,take a little on the low speed end.That's why the driver was given spark and fuel mixture controls.By the way it sounds I doubt you have a problem.
 
140 is too Cool for healthy engine life - the engine will suffer crankcase dilution and make sludge inside, even with modern oil!

Put a stat in it. 160 should be fine.

( I don't care that "Old Henry never used a stat", Packard and Cadillac did since about 1916, and Lincolns always used radiator shutters.)

If you're not using oil / blowing blue smoke, I wouldn't be terribly concerned.

Good Luck !
 
Thanks special coupe ; I am in Texas and it is starting to warm up. Only a few months out of the year where we can actually not continually be looking at the temp gauge. Won`t be long before ambient temp is 90-95 and temp gauge will be on 195 with AC running . Probably less than 100 miles put on engine at 140 .
 
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