1G Popping the oil cap. What could it be!?

[klipschaudio]

Hi, stock 1990 RS around 160k on clock, was fine but then started smoking and popping oil cap, issue came sudden.

Did compression test, was OK no major diff between cylinders.

Did a leak down test, all test around 20% at 15psi

Checked the PCV valve, blows out only, not in, ball is good.

Checked valve cover seems clean, blew air into pcv hole the air blows out of the other end.

I haven't driven the car in a while but I believe it smokes just idling now, if you drive it and give it some boost it will blow the oil cap off.

Stumped as to what could be causing this.

 

[motomattx]

Define "popping cap"? you might only need a new cap.

 

[klipschaudio]

Define "popping cap"? you might only need a new cap.

This issue had started around 2017 about 3000 miles of driving.

I first noticed pooling of oil in the valve cover indent, alot of oil, I believe I replaced cap with a new cap. Then I noticed the cap would be spun off and just laying on top of cover with oil in the indent.

I bet the metal retainer under the cap to make sure it holds very well and after just having reparked the car with zero boost I find that the oil cap basically lost it's retaining mechanism and it fell into the head luckily no damage.

The car does also smoke as well now...

So idk what is going on, maybe it's a combo issue with several defective caps coupled with real issue.

My next step is to take compression and to see what the blow by looks like with a paper at idle over the oil cap hole if I can get the engine to run again.

That's the oil cap that disintegrated looks like, the nut, retaining metal clip fell off and I have no idea how the tip of that center bolt got sheared off when the cap is sitting of top of the opening other then violent pressure but I still can't imagine it.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

Also I know hardened valve stem seals can cause smoke but usually only at acceleration, otherwise the car doesn't smoke as it idles. This car would smoke bad pretty much all the time.

I took the compression reading around 2019, and they were all showed low from what I recall with one being 10% or so lower then the rest, I will retest it.

 

[DSMTunedKvMan]

That's the oil cap that disintegrated looks like, the nut, retaining metal clip fell off and I have no idea how the tip of that center bolt got sheared off when the cap is sitting of top of the opening other then violent pressure but I still can't imagine it.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

Used any oil cap you want [modified-oem] make sure use OEM locking clip and 2xnuts if possible if not sit cap upside down tap bolt after nut install. Luck

 

[JusMX141]

Your cylinder head needs rebuilt. The exhaust valve stem seals are leaking pressure into the valve cover and it's overwhelming the PCV system.

 

[klipschaudio]

Your cylinder head needs rebuilt. The exhaust valve stem seals are leaking pressure into the valve cover and it's overwhelming the PCV system.

That night be the case, but isn't the sign of leaking stem seals was no smoke at idle and smoke UNDER load, no? Thanks

 

[klipschaudio]

Used any oil cap you want [modified-oem] make sure use OEM locking clip and 2xnuts if possible if not sit cap upside down tap bolt after nut install. Luck

You are saying that if I buy an after market cap, u need to pull the oem metal clip and install it on that cap securing with two nuts, if oem is not owned get that the aftermarket cap, place upside down and tap dorectly into the center of the retaining bolt and nuts, is that correct? If so, can you clarify what that accomplishes? Thanks

 

[klipschaudio]

Just did the compression test

Laser comp test

1 - 145psi
2- 138psi
3- 168psi
4-169psi

Nearly 20% diff between best and worst cylinder.

Would a leaking valve stem seal cause low compression? If so, am I safe to assume the rings are fine since I got a really good leak down test on all 4 cylinders? Thanks!

 

[DSMTunedKvMan]

2nd nut [will] secure bolt from losing the oem clip which will lock in place. Make sure rubber gasket its good condition not craked or worn.

 

[klipschaudio]

My brother said if you add oil to cylinder about half a cap full and do the test, if values change alot it's your compression rings, if they don't change much then it's your valves

Here is the test with both variants.

He said valve stem seals do not hold back the immense cylinder pressure, they only prevent oil from dripping down into the cylinders once the engine stops running that's why you see a puff of smoke at start up after car had cooled done but once it warms up it doesn't smoke.

I believe the issue is the bad compression rings at this point.

Laser comp test

1 - 145 (165 with oil added)
2- 138 (155 with oil added)
3- 168 ( 185 with oil added)
4-169 (175 with oil added)

I've added some pics of inside of cylinders as well.

Also I've read that a big sign of bad valve seals are spark plugs all oiled up, not the case with this car.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

 

[klipschaudio]

I'm also going to attempt to do a acetone/atf 50/50 mix and see if it will loosen stuck compression ring (probably just worn out though.)

 

[motomattx]

The cylinders look pretty good from what I can see, it seems that from the compression test that you may need new rings, do a leak down test to find out more information. Your oil cap falling apart has nothing to do with rings or compression though.

 

[DSMTunedKvMan]

Consider check for cracked valve guides or broken oil piston ring

 

[jed344]

Leak down test will tell a better story. I see you said above you did one but only at 15psi was 20% leakage? Should be done at a lot higher psi then that.