How bad is it to have oil on your spark plug threads?

[Newhart111]

I had a misfire code on cylinder 5, so I decided to start by first changing all the spark plugs (which it was time to anyway). I pull the spark plug for cylinder 5 and it looks like this:

Very bad right.. couple of other spark plugs also have oil on the threads but not as bad. It's only on the threads not the electrodes.

I also decide to swap the ignition coil with one in the front - #2 to see if that is the problem. The misfire code moves to cylinder 2 and cylinder 5 no longer has a code. This is telling me its the ignition coil. I change suspect ignition coil and the car is back to normal.

I'm not sure whether the oil on the threads was also contributing to the misfire, however the car is running now without any codes (with the new plugs).

----

The first time I changed the plugs on this car (that I bought brand new), some of the plugs already had oil on the threads. I suspect this car had a problem right off the line. The interesting thing is that many people with this same engine (Toyota 2GR-FE) have oil on the plug threads of the same exact cylinders. It seems it is a common problem with some Lexus/Toyota engines. I suspect that it is either, or both - the valve cover gasket or the spark plug tube gasket.


The question I have is: other cylinders were working fine without any codes while having oil on the spark plug threads. How bad is it considered to have oil on the Spark plug threads? Is a little bit to a moderate amount of oil not a big deal?

Another question I have is: is there an easy way to clean the oil off the spark plug threads on the engine side? Should I even bother doing it?

I'll come back to this thread in the afternoon to respond to replies. Thanks in advance.

 

[FowVay]

It's not a big deal but you do need to identify and correct the cause of the leak (needs plug tube seals and quite possibly the valve cover gaskets).

If it's time for a plug change then just throw those things in the trash and install a fresh set of exact replacement plugs. If you're going to reuse the plugs then spray them off with some solvent (brake parts cleaner), wire brush them to get any carbon out of the threads, and stick them back in (after the new gaskets/seal install). If you break any coil harness clips then replace them at this maintenance event.

 

[Newhart111]

If I put fresh plugs, should I clean the threads on the engine side. Is there a way to do that safely?

Should I be concerned about oil there? Does it impede the electrical connection?

If you look at the cylinder 5 plug - that’s a lot of oil. I imagine there is a lot of oil on the plug threads of the engine.

 

[Newhart111]

As far as changing the gaskets - I think I have a lot to learn before I can do that.

I also have to figure out what is inherent - maybe there’s a problem that doesn’t go away even if I change them.

 

[SC Maintenance]

The oil if it gets in the boot can cause a misfire. I would consider new valve cover and spark plug tube gaskets eventually.

Did the suspected bad coil have oil in the boot?

A cracked boot can cause a misfire also. Sometimes you can change just the boot, and sometimes not.

 

[Analog-1]

Seen this a million times with Honda engines. It's the spark plug tube seals and yes once it fills with enough oil it will cause a misfire. Easy fix though replace tube seals and valve cover gasket. If you have a cam plug seal replace that while your in there as well. Done..

 

[slo town]

Weird how it looks like the washer hasn't even been crushed.

Scott

 

[Gyro Gearloose]

Weird how it looks like the washer hasn't even been crushed.

Scott

I had the same comment. Looks like it wasn't fully torqued. I wonder it that oily goo is condensed hydrocarbons from fuel, oil, and partially burned hydrocarbons seeping past the threads.

 

[LongTime_Lurker]

This can be caused by a few different situations:

-Valve cover gasket or spark plug tube oil leak
-Excessive oil being burned in the combustion chamber
-Unburned fuel / soot accumulating on the threads over time

How far is this vehicle driven and does the engine reach operating temperature during this time? How long did your ignition coil last mileage-wise?

The porcelain and electrodes look relatively normal so you shouldn't worry about that substance unless there is a mechanical condition causing it. Inspect the area around the spark plug for any obvious signs of oil leaks and correct them if necessary. Clean spark plug threads are preferable as they will provide a better path to ground which is easier on ignition system components.

 

[Newhart111]

The oil if it gets in the boot can cause a misfire. I would consider new valve cover and spark plug tube gaskets eventually.

Did the suspected bad coil have oil in the boot?

A cracked boot can cause a misfire also. Sometimes you can change just the boot, and sometimes not.

There was no oil inside the boot. For #5 there was no oil anywhere which seemed like a mystery. So how would the oil get on the threads?

Maybe #2 answers the questions because there was a little evidence of oil:

It’s surprisingly clean down inside the tube.

So I guess what’s happening is it leaks from the spark plug tube seal, drips down to the plug and then down through the threads and whatever makes it to the electrodes gets burned up. I guess good thing it can make it down the threads, otherwise I would have oil pool up by the boot.

I feel like Toyota owes me and everyone else with this problem because like I mentioned, I believe it was there from when the car was brand new. I know because I’ve seen pictures of people who pulled the plugs on an almost new car and had the same problem on the same cylinders.

 

[Newhart111]

Seen this a million times with Honda engines. It's the spark plug tube seals and yes once it fills with enough oil it will cause a misfire. Easy fix though replace tube seals and valve cover gasket. If you have a cam plug seal replace that while your in there as well. Done..

Thanks I’ll have to look into what’s involved.

 

[bobdoo]

I think you could coat the spark plug insulator with dielectric grease, which is an insulator, and would stop oil short-circuiting the plug. A quick fix, for now.

And torque those plugs down per specs.

 

[Newhart111]

I had the same comment. Looks like it wasn't fully torqued. I wonder it that oily goo is condensed hydrocarbons from fuel, oil, and partially burned hydrocarbons seeping past the threads.

Its possible. I used a torque wrench (Precision Instruments split beam - supposedly same as Snap-on.)

A Toyota tech on a video said 13 ft-lb. I believe I did more. For now on I think I’ll use the technique to turn additional half turn after it stops.

 

[Newhart111]

This can be caused by a few different situations:

-Valve cover gasket or spark plug tube oil leak
-Excessive oil being burned in the combustion chamber
-Unburned fuel / soot accumulating on the threads over time

How far is this vehicle driven and does the engine reach operating temperature during this time? How long did your ignition coil last mileage-wise?

The porcelain and electrodes look relatively normal so you shouldn't worry about that substance unless there is a mechanical condition causing it. Inspect the area around the spark plug for any obvious signs of oil leaks and correct them if necessary. Clean spark plug threads are preferable as they will provide a better path to ground which is easier on ignition system components.

Yes I drive professionally for a car service.

These coils lasted 190k miles so far (5 still working). That one bad coil went out about a month ago (not sure how many miles). It doesn’t feel too great after I changed the plugs and that one coil - less power maybe.

I bought new set of Hitachi coils (all six). Going to change today and check plug gaps and reinstall. This time I’ll do 1/4 turn after seated or more if washer is not crushed.

 

[Newhart111]

I think you could coat the spark plug insulator with dielectric grease, which is an insulator, and would stop oil short-circuiting the plug. A quick fix, for now.

And torque those plugs down per specs.

I don’t think I have to worry about that since no oil is accumulating by the boot.

And that’s another mystery - how does oil make it past the crush washer?

 

[nascarnation]

Seen this a million times with Honda engines. It's the spark plug tube seals and yes once it fills with enough oil it will cause a misfire. Easy fix though replace tube seals and valve cover gasket. If you have a cam plug seal replace that while your in there as well. Done..

Here's what I don't understand.
If the spark plug is sealed to the cylinder head surface by the crush washer or tapered seat well enough to seal engine combustion gas pressure (500 to 1000 psi typical), how can it leak oil at atmospheric pressure going the other way onto the threaded portion?

 

[Newhart111]

Here's what I don't understand.
If the spark plug is sealed to the cylinder head surface by the crush washer or tapered seat well enough to seal engine combustion gas pressure (500 to 1000 psi typical), how can it leak oil at atmospheric pressure going the other way onto the threaded portion?

Good question!

 

[Gus_Mahn]

To me there's 0 evidence of that being a valve cover leak. I'd say that cylinder is burning oil, but not to the level where it's fouling the business end of the plug. Does the Toyota 2GR-FE have any history of oil usage? Does yours use oil between changes? Do you have a scope to look into the cylinders and maybe up at the valves?

 

[Accent Abuser]

I had a misfire code on cylinder 5, so I decided to start by first changing all the spark plugs (which it was time to anyway). I pull the spark plug for cylinder 5 and it looks like this:

View attachment 238426


Very bad right.. couple of other spark plugs also have oil on the threads but not as bad. It's only on the threads not the electrodes.

I also decide to swap the ignition coil with one in the front - #2 to see if that is the problem. The misfire code moves to cylinder 2 and cylinder 5 no longer has a code. This is telling me its the ignition coil. I change suspect ignition coil and the car is back to normal.

I'm not sure whether the oil on the threads was also contributing to the misfire, however the car is running now without any codes (with the new plugs).

----

The first time I changed the plugs on this car (that I bought brand new), some of the plugs already had oil on the threads. I suspect this car had a problem right off the line. The interesting thing is that many people with this same engine (Toyota 2GR-FE) have oil on the plug threads of the same exact cylinders. It seems it is a common problem with some Lexus/Toyota engines. I suspect that it is either, or both - the valve cover gasket or the spark plug tube gasket.


The question I have is: other cylinders were working fine without any codes while having oil on the spark plug threads. How bad is it considered to have oil on the Spark plug threads? Is a little bit to a moderate amount of oil not a big deal?

Another question I have is: is there an easy way to clean the oil off the spark plug threads on the engine side? Should I even bother doing it?

I'll come back to this thread in the afternoon to respond to replies. Thanks in advance.

You probably have a valve cover gasket leaking. Keep in mind this will ruin the new plugs and even the coils so your misfires will return if you don't address it.

 

[someonesomewhere]

If it was a valve cover gasket issue, there would be standing oil in the spark plug wells. Your socket would look like it had been dipped in oil when you pulled it out, because it would have been. The spark plug porcelain at the top would be oily. That just looks like normal thread carbon buildup. Remember, the threads don't seal to anything, only the crush washer or the machined seat surfaces do. To me, this appears as much-ado-about-nothing.

Drive it a few thousand miles, and pull a couple of coils and plugs, if everything is dry/clean except for the threads, and you're clear to keep driving with no further action required. Those plugs show absolutely 0 topside oil contamination currently.