Resolved Leaky Oil Cap

sinned4g63 · Sep 5, 2020

Yep, I know it's been beaten to death many times. :beatentodeath:

This past week I changed out my valve cover because it was cracked by the bracket that holds 2 of the spark plug wires on the bottom right corner of the plug well, the well usually had some oil sitting in it and I knew it was cracked from when I tried to paint it many moons ago. Now that I've got a replacement on being overly careful tightening the bolts because that's how I cracked the last one, I'm still getting oil in the plug well. I've wiped it off multiple times only to find more oil is being pushed from the cap itself. I tightened the hardware to stop it coming through the middle nut/bolt, but is continues to leak from under the cap. I got a new gasket and doubled up but still nothing even though the cap feels a lot tighter. When changing the valve cover I did also have to re-use the PCV at the top left corner but I blew through it and it seemed to be working as it should. The cap is probably a year or two old so I'll probably replace it and throw the new gasket on but I'm not sure what else I can check.. I have been searching for solutions on the issue periodically throughout the week but am having difficulty seeing people share their solutions and how well they worked.

Thought about getting a Mishimoto cap or something but that would be a shot in the dark, I'm not sure an aftermarket cap is the solution quite yet.

Fyke · Sep 5, 2020

In many cases the best will be to clean it up thoroughly. Start the vehicle and check it to see if you can see where it might be coming from if need be operate the throttle at the throttle body. If you're still having a hard time tracing the exact source there is a diagnostic tool called trace powder that we use at the dealership that makes it much easier to determine the source. I've also used UV oil dye in the past as well. Are you using an OEM cap?

https://www.maperformance.com/produ...2006-mitsubishi-lancer-evolution-8-9-mn163112

This is my go to replacement caps for the 4G63 that don't tend to leak at all!

sinned4g63 · Sep 5, 2020

Fyke said:
In many cases the best will be to clean it up thoroughly. Start the vehicle and check it to see if you can see where it might be coming from if need be operate the throttle at the throttle body. If you're still having a hard time tracing the exact source there is a diagnostic tool called trace powder that we use at the dealership that makes it much easier to determine the source. I've also used UV oil dye in the past as well. Are you using an OEM cap?

https://www.maperformance.com/produ...2006-mitsubishi-lancer-evolution-8-9-mn163112

This is my go to replacement caps for the 4G63 that don't tend to leak at all!

It is OEM but for an Eclipse. I'm not having issues finding where the oil is coming from, it's definitely the cap. I just don't know why when everything seems to be normal (other then the leak). It's wrinkle black so it's very easy to see where it's wet.

Fyke · Sep 5, 2020

No damage to the seal of the cap when you look at it?

pauleyman · Sep 5, 2020

How are your leakdown numbers and how is the valve cover vented? If its going to a filter or open atmosphere catch can that can cause issues. If you have excess crankcase pressure it has to go somewhere.

Fyke · Sep 5, 2020

To go along with my above comment I'd verify that cap just isn't shot/torn seal, but If all that is in check I would start suspecting the PCV system. I recently had a PCV Valve fail that I still couln't blow through, but was still allowing boost pressure to enter the PCV system. This thread is a very helpful one on that side of things

https://www.dsmtuners.com/threads/the-4g63t-pcv-system.366890/

lasthope05 · Sep 5, 2020

sinned4g63 said:
It is OEM but for an Eclipse. I'm not having issues finding where the oil is coming from, it's definitely the cap. I just don't know why when everything seems to be normal (other then the leak). It's wrinkle black so it's very easy to see where it's wet.

Is the oil cap face on the valve cover bare metal or powder coated too? I've seen amateur powder coaters not mask that area off before and it will cause issues.

sinned4g63 · Sep 5, 2020

lasthope05 said:
Is the oil cap face on the valve cover bare metal or powder coated too? I've seen amateur powder coaters not mask that area off before and it will cause issues.

It is bare metal, I spray painted it myself and always tape off the "sealing" surfaces.

Fyke said:
No damage to the seal of the cap when you look at it?

It was brand new from extremepsi. I took a good look at it beforehand and didn't notice anything.

Fyke said:
To go along with my above comment I'd verify that cap just isn't shot/torn seal, but If all that is in check I would start suspecting the PCV system. I recently had a PCV Valve fail that I still couln't blow through, but was still allowing boost pressure to enter the PCV system. This thread is a very helpful one on that side of things

https://www.dsmtuners.com/threads/the-4g63t-pcv-system.366890/

I wouldn't mind trying an evo cap like you suggested. The design seemingly having a solid top as opposed to the eclipse having a nut and bolt through it for the tabs just sounds better all around. But like I said I can blow through that valve I carried over, what other ones should I check?

Edit: I should also mention I read somewhere that turning the VC oil cap back just a hair until its firm might be a simple fix.. I've done that since leaving work today and it did feel tighter but I haven't popped the hood since. I'll have to check.

pauleyman said:
How are your leakdown numbers and how is the valve cover vented? If its going to a filter or open atmosphere catch can that can cause issues. If you have excess crankcase pressure it has to go somewhere.

Unfortunately if it's not my cap it sounds like excess crankcase pressure.. everything is a stock setup for me with the only recent changes being a good VC, injen intake and cone filter, and a Greddy BoV. The VC had its vacuum lines hooked up stock routing otherwise. I've never done leak down, only compression which showed surprisingly good.

Fyke · Sep 6, 2020

My recommendation would be to order and replace a PCV Valve with a new OEM one and reevaluate. If it still has an issue I'd look at the cap at that point. PCV valve change is good maintenance and theyre not super expensive either.

steve · Sep 7, 2020

sinned4g63 said:
When changing the valve cover I did also have to re-use the PCV at the top left corner but I blew through it and it seemed to be working as it should.

You can't check that it works by blowing through it, only that it's broken if you can blow in both directions. The valve must seal against boost pressure in the intake manifold and not leak. Almost all new ones do leak right out of the package.

sinned4g63 · Sep 8, 2020

steve said:
You can't check that it works by blowing through it, only that it's broken if you can blow in both directions. The valve must seal against boost pressure in the intake manifold and not leak. Almost all new ones do leak right out of the package.

I could only blow air one way which would be flowing out of the VC, is that what you mean?

sinned4g63 · Sep 8, 2020

Fyke said:
My recommendation would be to order and replace a PCV Valve with a new OEM one and reevaluate. If it still has an issue I'd look at the cap at that point. PCV valve change is good maintenance and theyre not super expensive either.

Might just order both.. they get stuff to me like next day with no fancy shipping.
https://www.extremepsi.com/store/OEM-Oil-Filler-Cap-Mitsubishi-Lancer-EVO-VIII-and-IX.html
https://www.extremepsi.com/store/OEM-PCV-Valve-Mitsubishi-Eclipse-90-99.html

Fyke · Sep 8, 2020

sinned4g63 said:
Might just order both.. they get stuff to me like next day with no fancy shipping.
https://www.extremepsi.com/store/OEM-Oil-Filler-Cap-Mitsubishi-Lancer-EVO-VIII-and-IX.html
https://www.extremepsi.com/store/OEM-PCV-Valve-Mitsubishi-Eclipse-90-99.html

That would be a great route to go! From reading and my understanding is the blow test is kind of a false positive in a lot of cases. We can't really produce boost pressure with our lungs so sure it may hold back when blowing into it, but under boost is a whole different beast. Personally I replaced a PCV valve recently on a hunch on one of my vehicles even though it had passed a blow test and it took care of some oil consumption issues and rough idle issues I had been experiencing.

sinned4g63 · Sep 8, 2020

Fyke said:
That would be a great route to go! From reading and my understanding is the blow test is kind of a false positive in a lot of cases. We can't really produce boost pressure with our lungs so sure it may hold back when blowing into it, but under boost is a whole different beast. Personally I replaced a PCV valve recently on a hunch on one of my vehicles even though it had passed a blow test and it took care of some oil consumption issues and rough idle issues I had been experiencing.

Yeah I wasn't really sure how else to check it but I definitely can't make 14-16 pound of boost with my lungs.. Cheap enough to replace though that I should have done it beforehand. Thanks for the feedback, I'll get them on order now.

steve · Sep 8, 2020

You have to use compressed air.
Sadly, almost all of the cars that use the same PCV are NA and the ability to seal under positive manifold pressure isn't a key design feature, so they don't, even brand new. So you have to test each and only use those that work.

You find threads here describing the use of check valves and some of the pitfalls of using them.

sinned4g63 · Sep 8, 2020

steve said:
You have to use compressed air.
Sadly, almost all of the cars that use the same PCV are NA and the ability to seal under positive manifold pressure isn't a key design feature, so they don't, even brand new. So you have to test each and only use those that work.

You find threads here describing the use of check valves and some of the pitfalls of using them.

So basically cross my fingers and hope that I get one that works on the first order?

chrysler kid · Sep 11, 2020

I'm convinced the oil baffle for the pcv system and the cap design and location are not adequate for an older model dsm with a little bit of blow by from the piston rings.

1gs seem to pop out the dip stick, 2gs seem to push oil out of the filler cap

sinned4g63 · Sep 25, 2020

Installed the cap and PCV and seems to have fixed the leak. Still some residual in the spark plug well where its difficult to dab up with a rag but it certainly isn't accumulating anymore. The area around the cap is completely dry now.

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