Recently replaced my cracked exhaust manifold and eliminated all exhaust leaks. (Running 14psi.) Took the car out on Friday for a tuning run and noticed a lot of blue smoke out the tail pipe when letting off the accelerator and when really getting on it. Pulled over, lifted the hood and noticed oil leaking from around the oil fill cap. Cleaned it up and then went to an autocross on Saturday morning. When I arrived at the event, there was more oil around the cap. Talked to some other fellow Miata-ers and they thought the PCV valve was bad and one suggested removing the PCV valve and capping where it was connected to the intake manifold. They thought there might be a little oil that might escape but it shouldn't be much. Wrong. After my first run, I lifted the hood and the passenger side of the engine bay was covered in oil. Got the car home and just did some diagnostics tonight.

* Ran borescope down each cylinder to see if there was any visible damage. They all looked ok but there was a little bit of oil in all cylinders but mostly in 3 and 4.
* Spark plugs looked ok.
* Did a leak test and found that cylinders 1 and 2 held 50 psi with no leak.
* Cylinders 3 and 4 only held about 10-15 psi when pumping 50 psi.
(I'm not sure I'm describing that correctly, but maybe you understand what I mean.)
* Put thumb over PCV valve opening and hand over the oil fill hole and could feel air pressure.
* Pulled the valve cover off and, while compressing cylinder 3, could hear and feel air coming from the vertical oil channels on the intake side around cylinders 3 and 4.
* Oil looks fine so figure no coolant getting into the oil.

Did fixing the exhaust leaks cause the head gasket to blow due to the increased pressure? Is the air that is going through those oil channels keeping the oil from flowing down from the head into the block?
Any other thoughts or advice?

Thanks.

 

Sounds more like you may have cracked/melted ringlands. Either way you need to just go ahead and pull the head off. You will know for sure what youre dealing with.

 

I love the friend who says" PC might be clogged, just cap it".

 

Valve stem seals perhaps?

 

your engine is ready for a build

 

I was going to vote ring/piston issue as well. Without knowing how bad it is, it seems possible that a catch can and new oil cap oring could buy you a little more time. At least it's not spitting the dipstick out yet!

 

Your post contains a list of symptoms of ringland failure. Blue smoke under power, oil residue from oil fill cap, excessive blowby from valve cover breather, wet cylinders, high leakdown percentage with air bypassing into crankcase. Nothing you said indicates any issue at all with the head gasket.

For anyone who finds this thread in future searching, let me help you out. There is a very simple litmus test for "does my Miata have a bad head gasket".

• If the engine runs, AT ALL, it does not.
• If the engine turns over freely, sounds like it has zero compression, and will not even come close to starting, and you have recently overheated it catastrophically, then you have a bad head gasket.

This is not a Subaru or Honda engine. It's a closed-deck iron block and a factory MLS gasket. The rods will exit stage left far, far before the head gasket is compromised from excess cylinder pressure.

 

The Miata head gasket will fail when the car is overheated and the car will still run contrary to what stated above.

But, as stated above, you do not have a failed head gasket. You have broken rings and or broken ring lands due to a timing problem, a fueling problem, or both.

 

I ran my car with a bad head gasket for some time this summer, and it actually ran pretty well. It kept pushing coolant out of the overflow tank due to cylinder pressure in the coolant system. I just would keep adding coolant and running it that way until I got another engine to replace it. Not all head gasket issues are so severe that the car wont start and run.

 

1.6 or 1.8?

 

1.8, I know the 1.6 doesnt use an MLS as OEM and the 1.8 does. I bought the car used with a ton of miles and apparently the previous owner had changed the HG. Im thinking the head was warped or it wasnt installed correctly. I still havent torn down the motor to confirm but all signs pointed to blown HG.

**Sorry to get off topic**

 

I have a 1.8. Last summer, I had a leak in the hose feeding water into the turbo, lost all my coolant, and overheated. After that, I definitely had a blown head gasket because during a compression test, I was blowing coolant out of cylinders 3 and 4. Had the head resurfaced and a valve job. The block flatness checked out ok. Put everything back together with a head gasket the speed shop got for me. Did another compression test and coolant still blew out of 3 and 4. Got an OEM head gasket and that seemed to fix that problem. Been driving it regularly since then; daily driver for a few months and about 6 autocross events. Everything was good until fixing my exhaust leaks recently...

After I posted on here, the friend helping me suggested I loosen the head studs and re-torque them. Tonight, when I loosened them, the ones around cylinders 3 and 4 were clearly looser than the others. Do you suppose it's possible that there is a minute path for compression to escape into an oil passage?

Plan to do another leak down test tomorrow.

 

Dont reuse head bolts..

 

Thought you could reuse ARP head studs.

 

Thought you said bolts. Studs are fine to reuse. My mistake