Hello,

I was doing spark plug maintenance on my Lexus and as I pulled plug #5 I noticed it had coolant and oil on it around the threads, does this definitely mean a head gasket issue if no other plug had coolant on it? Is there a possible leak from a temp sensor or sender unit?

I also noticed each plug had a decent amount of oil on the threads with the valve cover not leaking into the spark wells, where is the oil coming from?

The compression tests on each cylinder ranged from 145-160 with no leaks detected. I'm not sure how the car is burning oil if the valves, rings and cylinder are holding decent pressure.

Not sure what to do next. I've attached pictures of plug #5 with coolant and oil and pictures of the cylinders from an endoscope. Any and all advice and opinions are appreciated.

Edit: After looking at each plug, almost all of them seem to have coolant on them, hence the steam clean cylinders in almost all the cylinders. It's likely 100% a head gasket. Yay 😊 Rebuild with lots of power?

Thanks 🙏

Cylinder #6 , also oddly clean with some built up of carbon deposits

Cylinder #5 , too clean, from coolant getting in cylinder with deposits visible

Cylinder #4 , relatively dirty with carbon deposits visible

Cylinder #3 , relatively dirty with carbon deposits visible

Cylinder #2 , relatively clean with some oil visible

Cylinder #1 , relatively clean with some oil visible

Spark plug from cylinder #5 coolant, rust and oil on the threads

 

Hello,

For the Pistons to get to that level of clean, at the very least you will see the Coolant Level drop every time you go for a ride, not to mention the consistency across 5 out of 6 Cylinders. My point is, before tearing into the Engine, invest in either a blow-by (here), or leak-down (here) tester, preferably both, it would be an objective, definitive proof on whether you need a new Head Gasket at this time, and at least last time I checked, those testers cost considerably less than rebuilding half of the engine..

Hope this helps and best of luck!

 

Arsenii,

This helps a ton! Thank you for the response. The weird thing is this, the radiator is totally full and doesn't show signs of consumption.

It does read slightly higher than the gauge should sit at for OE temps, but it doesn't really over heat, so to speak. Like there isn't any smoke out of the tailpipe and the radiator is always topped off.

Backstory, I bought this car at auction at the start of summer 24'. Never really dug into it aside for fixing an exhaust leak and having mufflers welded on. Wanted to get it road legal for emissions where I live in Colorado and started with a tune up. Plugs clearly showed signs of oil and coolant leaking and oil consumption. There is a noticeable lack of power in second gear and thru the power band which I was assuming was the clutch and transmission, but this shows otherwise.

Next step is a leak down, which I've never performed. What will this show?

 

Got to give you credit here, if any work at all is being done on the exhaust of those cars, it's usually quite the opposite unfortunately..

There is a reason Spark Plugs have a Crush Washer on them, the thread alone will not create a proper seal, but what it can do is start trapping some of the material that ends up in the Combustion Chamber, which is why the Thread can end up being Wet, while the rest of the Spark Plug is Dry. Aside from the fact that it has been a while since that Spark Plug was replaced, and an apparently damaged Boot on the Spark Plug Wire judging from all the Gunk on the Insulator, I honestly can't see anything in the picture that you posted that would be a cause for concern. And as for the Oil Consumption, for the engine well into 6 digits on the odometer, which I presume is the case here, it is just the unfortunate reality that you will have to deal with.

One thing I neglected to mention is that you will need at least some type of Air Compressor, even the most basic one will do, at least if your Engine isn't completely shot.. If you don't have it, I would suggest starting with the Blow-By Test first, below is a video on how that works.


Back to Leak-Down Test, the idea is quite simple - you Pressurize the Combustion Chamber through the Spark Plug Hole and see where the Air escapes. The leak-down tester is nothing but a set of manifolds screwed together, one shows pressure coming In, the Pressure of your Compressed Air, the other pressure coming Out, the Pressure inside of the Combustion Chamber. The difference in those Pressures, the Pressure Drop that occurs as the Air escapes the Combustion Chamber determines the Severity of the Leak, the bigger the difference, the more Air finds its way around the Combustion Chamber, the Sound of Air Escaping determines where it escapes, if you hear the air in the Intake or Exhaust, one of the Valves is not seated correctly, if you hear it in the Dipstick or PCV Line, the Piston Rings are busted, if you see Coolant start to Bubble, then you know you have an issue with the Head Gasket.

Below is a video that shows how to use this tool, the design is a little different, but the concept is still the same. Do keep in mind though that you are working with Pressurized Air here, there is a chance that if you are not perfectly at Top Dead Center, the Cylinder may shoot down without warning when you pressurize it, it won't damage the Engine, but it will for sure cause havoc if you leave the wrench of any kind on the Crank Pulley Bolt before pressurizing the Cylinder, so make sure to remove anything that is not part of the Engine out from the Engine Bay, especially if it's near anything that rotates, before connecting the Air Hose.


Hope this helps and best of luck!

 

Aha! Thank you for the detailed response and break down. You are truly a gem of a person.

I'm going to harbor freight tonight to get a leak down tester and a stethoscope to listen to the leaks. I'll also be using some small tubing to amplify the noise once the system is pressurized.

As for the compressor, I just got one last week at a garage sale! Winning.

 

Arsenii!

Just completed the leak down test and it isn't a head gasket, which is good, but the 5 & 6 cylinders are leaking terribly on the intake side and passed the rings.

When watching the cylinders with an endoscope to get to TDC I also saw exposed metal on the tops of pistons 5 & 6 on the intake side. Which tells me the valves are not sealing properly on that side and the valves need to get worked on. Pistons are probably okay, slight marking on them but no damage to the walls or the integrity of the piston.

Another weird thing that was revealed between 5 & 6 was the source of the leak, I could feel air coming out of cylinder hole #5 when testing #6 and vice versa. Double checked to make sure the tester was sealed and it still happened. Almost felt like it was coming out of the valve cover gasket.

Results of the leak down
Cylinder 1 - 75/80psi - air hissing out of oil filler
Cylinder 2 - 64/80 air hissing out of intake manifold
Cylinder 3 - 78/80psi air hissing in oil filler
Cylinder 4 - 78/80psi air hissing in oil filler and intake manifold
Cylinder 5 - 26/80psi air hissing out of cylinder #6 and oil filler
Cylinder 6 - 48/80psi air hissing out of cylinder #5 and oil filler

Attached are some photos of the pistons and intake manifold. Please give me your thoughts and potential next steps. Will probably send out the head to get worked on.


Cylinder 5 and 6 spark plug wells, cylinder 6 is in the rear closest to the firewall. This is where you can feel air in either cylinder leaking by.

Top of piston #6 with exposed metal visible and shiny

Top of piston #5 with valve damage , exposed metal is visible and shiny

Intake valve from inside manifold

Another intake valve from inside manifold view

 

Did you make sure to do the test with the Engine on the Compression, and not on the Exhaust Stroke? With the way a 4-Stroke Engine works, there will be 2 times the Piston will reach TDC - the First time when it Compresses the Air/Fuel Mixture to Ignite it (Compression Stroke), and the Second Time, after the Piston is pushed down by Combustion, when it comes back up to Vent the Exhaust Gasses (Exhaust Stroke), refer to the animation below for a visual of the process.



When performing this test, you have to set the Engine to the Compression Stroke, not the Exhaust Stroke, otherwise you will get the symptoms you described earlier. Try repeating the test, take the Upper Timing Cover off and align All the Timing Marks, that way you will know that Cylinder 1 is currently at TDC of the Compression Stroke, and perform the test again, then follow the Firing Order for the next Cylinder to check, which, for 2JZ appears to be 1-5-3-6-2-4, that way you won't have to think about which Cylinder is at Compression Stroke.

With that, other than Cylinders 5 and 6, which, again, I am pretty sure are a result of the test being conducted incorrectly, those numbers look markedly better than for most engines I've ever worked on, there is barely any air that finds its way past the Combustion Chamber, so you really don't have anything to worry about, so long as the other Cylinders will show similar numbers if the test is conducted correctly that is.

Hope this helps and best of luck!

 

Unfortunately it is the compression stroke, I made the mistake of doing it during the exhaust stroke and the numbers dropped out to about 8psi, I then turned the engine 180° to compression and retested multiple times to make sure I didn't miss anything. The numbers were above 8psi but way below what they should be for a healthy engine. Each time the numbers matcher what I posted above I'm kind of dead in the water right now 😅

 

Well, it does appear that you are at the point when one starts counting money..

It's hard for me to say anything definitive without actually being there to observe the test procedure, and this is the case where it is quite important. I would probably suggest getting a second opinion, find a local mechanic that would be willing to either do the test in front of you, or observe from the side as you do it, and perform this procedure again, that way the mechanic would be nearby to spot any potential issues, either with the engine or the test procedure, even though I can't really think of such mistake in the test procedure that would cause the Air to leak from one Cylinder to the other. Either way, it's a simple enough procedure, it will cost a lot less to do a thorough test than to pull the Head and realize that it was fine all along.

That said, should you decide to ignore the advice above and pull the Head anyway, before doing anything to the Engine, find a Machine Shop first and make sure that they will take your Head for repairs, those are getting few and far between, at least in the area that I am in, and get all the parts that you will need for this project, lest you end up with an anchor for however long it takes to source that one part that, as it turns out, is no longer in production and can only be hand-delivered from another end of the world, that way the car is at least somewhat driveable in the meantime.

Hope this helps and best of luck!

 

This will be my next move. I can drive the car short distances, don't want to risk anything long term. But I did the test multiple times and made sure I was doing it right... It was nerve wracking thinking I was wrong and then finding out again I was right and either the head gasket or the block itself is leaking by. Not sure. But a second opinion would not hurt.

Thank you for the responses, really helpful.