Oily Spark Plug, Should I Go Thicker?

[camrydriver111]

Hi All,

I recently did the spark plugs in a Mazda 3 Skyactiv 2.0 with only 120,000 km. There was no CEL, it was preventative maintenance.

3 of the spark plus were fine. 1 was slightly oily.

The car has had regular changes with 0W20. The oil level practically doesn't change between OCIs (8000 km to 10000 km).

I am thinking about switching from 0W20 to 0W30. I'm thinking that once 0W30 gets sheared and diluted it will be 0W20.

However, fans of the Skyactiv engine are usually really adamant about 0W20 and most UOAs come back really clean.

Is there any issues with going up to 0W30 and could it help the oily spark plug situation?

 

[BMWTurboDzl]

If there's oil on the threads it could be a bad valve cover gasket.

 

[camrydriver111]

The spark plug holes themselves are clean. The oil is concentrated on the lower portion of the threads.

 

[KrisZ]

You sure it’s oil and not just normal soot?

 

[dwendt44]

You could go with 5W-30. That engine is near bullet proof and it's rated for the 30 weight in
most parts of the world.

My 2¢

 

[JohnnyJohnson]

Hi All,

I recently did the spark plugs in a Mazda 3 Skyactiv 2.0 with only 120,000 km. There was no CEL, it was preventative maintenance.

3 of the spark plus were fine. 1 was slightly oily.

The car has had regular changes with 0W20. The oil level practically doesn't change between OCIs (8000 km to 10000 km).

I am thinking about switching from 0W20 to 0W30. I'm thinking that once 0W30 gets sheared and diluted it will be 0W20.

However, fans of the Skyactiv engine are usually really adamant about 0W20 and most UOAs come back really clean.

Is there any issues with going up to 0W30 and could it help the oily spark plug situation?

Really over one the Mazda forum I've noted people using 5W-30 https://mazdas247.com/forum/categories/mazda-cx-5-forum.549/

But the oil isn't the issue or all 4 of your plugs would be oily!

 

[RDY4WAR]

First, you need to figure out where the oil is coming from. If it was mine, I'd do a compression and leakdown test of each cylinder. If that checks out, then the rings can be ruled out and the intake valve seal is the likely culprit. If you get high leakdown in that cylinder, indication of a bad rings, then it's a crapshoot as to whether higher viscosity will make it better or worse. Sometimes higher viscosity can make consumption worse around the rings due to the thicker oil film permitting more oil transport past the rings. Sometimes, it creates more of a "gasket" for the rings to help them seal and reduce consumption. It's hard to say which it is without tearing the engine down.

If a valve seal is the culprit, you can try an oil that contains a good bit of ester to try to condition the seal and slow or stop the leak. That also depends on the seal material which I'm not sure about for that engine.

 

[Vermess]

If you don't think that your vc is leaking, no oil is going to fix your situation, bud.

You have to find out if oil is getting past the rings. If so, some engine cleaner or oil high is esters will free them up.

I have had good luck with a simple bottle of windex filled with water sprayed next to the throttle body allowing the engine to suck that in....that worked like magic in a couple of scion TC's.

 

[Vermess]

First, you need to figure out where the oil is coming from. If it was mine, I'd do a compression and leakdown test of each cylinder. If that checks out, then the rings can be ruled out and the intake valve seal is the likely culprit. If you get high leakdown in that cylinder, indication of a bad rings, then it's a crapshoot as to whether higher viscosity will make it better or worse. Sometimes higher viscosity can make consumption worse around the rings due to the thicker oil film permitting more oil transport past the rings. Sometimes, it creates more of a "gasket" for the rings to help them seal and reduce consumption. It's hard to say which it is without tearing the engine down.

If a valve seal is the culprit, you can try an oil that contains a good bit of ester to try to condition the seal and slow or stop the leak. That also depends on the seal material which I'm not sure about for that engine.

With 75k miles on the engine, I was leaning more towards a stuck ring than seals. Never seen a Mazda engine or any jap 4 banger lose the valve seals at such a low mileage....except Subaru.

 

[Lubener]

The spark plug holes themselves are clean. The oil is concentrated on the lower portion of the threads.

If it's not on the electrode, I wouldn't worry about it.

 

[Vermess]

If it's not on the electrode, I wouldn't worry about it.

I would. Any oil on the treads I'd be worried about.

what people don't realize/know is that one of the main functions of the thread/body of the spark plug is to transfer heat from the plug and chamber into the head. Having a barrier between the threads and the head could cause a insulation barrier causing that plug/cylinder to run hot leading to pinging....that opens up a can of worms.

 

[DGXR]

Does the oil level stay consistent over a service interval, or is it losing oil? If it loses oil, are there leaks or does it consume the lost oil?

 

[KrisZ]

I would. Any oil on the treads I'd be worried about.

what people don't realize/know is that one of the main functions of the thread/body of the spark plug is to transfer heat from the plug and chamber into the head. Having a barrier between the threads and the head could cause a insulation barrier causing that plug/cylinder to run hot leading to pinging....that opens up a can of worms.

A thin film of oil does not impede heat transfer. Not sure where people pull their theories from.

 

[Vermess]

A thin film of oil does not impede heat transfer. Not sure where people pull their theories from.

It's not a theory, it's fact. Thin film or not, it had an effect.....in today's high compression engines, turbo engines, etc, it has a big effect.

As a matter of fact, most plug manufacturers recommend against any oil or antiseize on threads of plugs for the exact same reason I depicted above. But what do they know? They just make the stuff.

Regardless who's right or who's wrong, the dude has oil coming past the rings. That needs addressing and no change in oil grade will fix it. Mitigate it? Maybe.

 

[ZeeOSix]

It's not a theory, it's fact. Thin film or not, it had an effect...

What medium transfers (conducts) heat better ... oil or air? Oil on the threads doesn't really change the actual metal-to-metal contact heat transfer path - the heat transfer medium thickness is near zero in the areas where the threads make contact. If oil fills the air gap areas between the threads, it may actual help the heat transfer. Air can act like an insulator, then it would be radiative heat transfer in those air gaps, which isn't very effective. In any respect, if there is a difference in heat transfer, it's too slight to actually matter.

 

[ZeeOSix]

Check to see if the oily plug is the cylinder that's closest to where the PCV connects to the intake manifold.

 

[camrydriver111]

These are the plugs

 

[bobdoo]

As every PC overclocker knows, two bare metal surfaces don't have enough contact to effectively transfer heat. That's why very expensive (by weight/volume) thermal compounds are used. Oil will conduct heat through surfaces that otherwise wouldn't touch.

Oil is an insulator, so if it *did* prevent *all* metal contact, spark would diminish.

 

[ARCOgraphite]

As every PC overclocker knows, two bare metal surfaces don't have enough contact to effectively transfer heat. That's why very expensive (by weight/volume) thermal compounds are used. Oil will conduct heat through surfaces that otherwise wouldn't touch.

Oil is an insulator, so if it *did* prevent *all* metal contact, spark would diminish.

My old Pentuim is getting 7 years on. Not Gaming and overclocking, but do you recommend I take off the heatsink and clean and repaste it with fresh compound? Do you find they dry up on a medium case desktop? I jknow laptops cook.

Thank You - Ken

- sorry guys about the mini hijack.

 

[KrisZ]

My old Pentuim is getting 7 years on. Not Gaming and overclocking, but do you recommend I take off the heatsink and clean and repaste it with fresh compound? Do you find they dry up on a medium case desktop? I jknow laptops cook.

Thank You - Ken

- sorry guys about the mini hijack.

Yes, the usually cheap thermal pastes used on stock cpu coolers do dry out.
However if you are not experiencing elevated temps, a new paste will not make much difference.