Smoke coming from Catch can (video), low compression
 

The motor has about 170k miles and low compression across the board. Bought the car this way and is running a ebay setup at 8 psi.

dry: 90, 115, 70, 115
wet: slightly higher but not a huge difference

The motor was blowing air out of te dip stick and often knocked it lose out of the slot. Also oil was found in the intercooler pipping. I added a catch can to help relieve the positive pressure in the head. I set it up using the two valve cover ventilation ports and capped off the MAF and intake manifold ports (like pictured in the video).

After taking it for a test drive there is constant stream of smoke coming out of the catch can vent and exhaust.

VIDEO: (click to view)
https://www.miataturbo.net/attachmen...ine=1331004699

option 1:
Is there any chance I have a blown head gasket and am burning coolant which would also contribute to the low compression

option 2:
or is there a problem with my piston rings and I am getting excessive blow by and burning oil (need a new motor)

option 3:
other??? :hustler:



any input would be greatly appreciated. Thanks!

Very blown motor. Time for a new one.

glad to hear im not the only one dealing with this problem lol! I ran the vent tube out of my wheel well so i dont have to see smoke coming out of my hood.. ive only got low comp on cyl#1 its at 120.. but i think i also have an external headgasket oil leak... Sucks cus i just did a headgasket but didnt resurface the head like a dumbass... But i cant seem to pinpoint the leak after regasketing everything twice.... oh well pickin up a new motor this week.

Ya, i figured. Just wanted to double check before pulling the motor. Thanks for the help!


Try a leak down test. It would be very helpful to pinpoint the problem since only one cylinder is bad. My entire engine is messed up and all cylinders are crap so i guess theres not use in that for me...

I have a spare engine in my garage that I am doing maintenance work on before I drop it in. Hopefully that will solve all my problems.

Rev it up, see how much more smoke comes out :P.


Check the radiator, any bubbles coming out of the over flow tank?

I would say its your rings. A blown head gasket would show much more smoke in my opinion.

those compression numbers are pretty terrible, and cyl 3 is especially bad. sav's response is most appropriate. at this point, it doesn't really matter whether it's rings or HG (smoke looks fairly white for it to be JUST oil), that motor needs to be replaced/refreshed. not a ton of value in diagnosing it further, i don't think.

Drop new block in then bore,skim and build the old one for FI. Then drop in back in.

thanks for the input sire.

I agree. New motor going in soon. thanks for the help.

I'm just gonna run 8psi for a while so I'm hoping a stock block will hold up fine for a while. Ill definitely keep it in my garage for a while if I want to up the boost and do a serious build. Thanks.

8 psi or a bit less will be fine, it shouldn't put any real strain on a stock motor at all.

I am having a similar issue but my compression numbers are good, engine was rebuilt but still blows oil out of oil cap. And smoke from catch can. Running FM upgraded pcv valve.