So I put about 70 miles on my 1992 and I started to notice bluish white thin smoke coming from the exhaust. I popped the hood and checked my PCV valve and when i did that a decent amount of smoke came out of the PCV opening. The PCV valve checked out so that wasnt the problem... My first thought was bad piston rings so i did a compression test. Cylinder #8 showed about 85psi while all 7 of the others were inbetween 170-180psi. I also lost a noticeable amount of oil without seeing any leaks anywhere. So what are my options here? could it JUST need new rings? seems like the cylinder wall is probably severly damaged if I had noticeable loss of oil. Im not sure I have the confidence to tear her down and get a look inside the cylinder so I just wanted to hear what others believe the problem to be. A bit of history, the car had new forged pistons put in MAYBE 300 miles ago but it sat for years after that. Maybe piston rings are stuck? Any help is greatly appreciated,

 

On one cyl? Id guess a head gasket, rings are probably fine.
Both valves were closed when you did this?

 

Yea just cylinder #8. Both valves were closed. The spark plug from cylinder #8 was also covered in black soot. All others looked like they were operating in good conditions. The loss of oil made me believe it was not a blown head gasket, is that an improper assumption?

 

Did you do the pistons? Are you positive it ran perfectly 70 miles ago? 300 miles does not seem like enough to build up anything that could stick the rings. Could a ring have been broke on the install? Myself, I would pull the plug and put something in the cylinder like seafoam, deep creep, atf and acetone just something to loosen the rings if they are stuck. Let it soak in a few days. Put in a new plug and drive the **** out of it. If after this it is still low something is wrong inside. When you did the compression test did you add some oil into the cylinder to see if the compression went up? If it is rings the oil will help seal it very temporarily. Before planning on tearing it down I would do a leak down test as it COULD be a valve or as mentioned a head gasket. Dan

 

I did not do the pistons, they were done by the previous owner who is a friend of mine. Im quite confident he did them properly. I did another compression test this morning and then did it again with about a tablespoon of oil in the cylinder. the wet test was about 15 psi higher than the dry test. Ill put seafoam in there and let it soak for a while.

 

I would try using Marvel Mystery Oil in the #8 cylinder as it is a great penetrating oil. It is much thinner than most motor oils and helps free up sticky parts. I use a large syringe to put the oil in the cylinders individually. If the engine were still warm from running it might work better and faster. Heat helps oil creep into smaller gaps. The all time best penetrating oil (in my opinion) is made by KROIL's Oil and that stuff can get in between a Millionth of an inch according to the manufacturer. I have been using it for decades for removing stuck fasteners. Heat and Kroil's Oil will get most stuck fasteners freed up.

My 1968 C3's 427 sat for a while and it did the same thing, some of the plugs were black and sooty after starting it. It might have been due to the thicker oil I used to lubricate the cylinders before cranking the engine burning off. They were iridium Plugs and they got fouled very quickly by the oil I put inside the cylinders.

Before cranking it for the first time I run the oil pump with an electric drill to pressurize the oil system and get the stuff everywhere it is supposed to be. I also put 1-2 ounces of 30 weight motor oil inside the cylinders before cranking the engine. So I then went to a quart of Marvel Mystery oil added to an oil change. That works great but I would not drive it hard with the marvel Mystery oil diluting the engine oil.

From now on I will put Marvel Mystery Oil inside the cylinders in place of the 30 weight oil. Marvel Mystery Oil is really great if you have a noisy lifter.

A "Leak Down" Test might help you identify what is leaking better than just a compression test. It is a better test after you have identified a problem like low compression as it will show you what is leaking, valves, head gaskets, valve seals or piston rings. It is not a hard test to do and is less common than a compression test. They use it to monitor the Engines "Overall" Health in piston powered aircraft like my old Cessna 172. It is a great diagnostic tool that is starting to appear more often on cars as well. I use it on every gas engine I have with "issues" including lawn equipment. They are available on Amazon and a lot of auto parts stores. The one thing you will need is a good air compressor to be able to do the test.

 

Marvel is better than Seafoam for this. Dan

 

Leakdown test of effected cylinder. Then you should know if it's rings or head gasket. Bore scope in could reveal if piston is broken. Remove valve cover and look to see if valves are both there.