possible blowby?
 

I have a 91' caprice ltz with 183,000 miles on it. why is the oil coming up thru diptube? i replaced the pcv valve and there is suction when tested.

Suction at the PCV valve or at the dipstick tube?

Blowby would cause there to be pressure at the dipstick tube and breather. The PCV system will negate some of this, but if the blowby is too bad, it'll overwhelm the PCV system.

One reason for oil to be coming out of the tube is too high of an oil level. Another is if the bottom tube inside the crankcase was missing/broken off. But if you have a bad ring or piston, you may see a puffing of blowby from the open breather at idle (see video below).

It's time you did a few tests. A leakdown test would be preferred over a compression test, but either will show you if you have leakage past the rings. A vacuum gauge can tell you quite a bit if you interpret the readings correctly.

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would a heavier oil or oil additive help?

Do the tests cobalt suggested.

In order for the pcv to work you need a fresh air supply into the motor. Check it first. Should be on the opposite valve cover to the pcv.

You need to diagnose the problem, then you can make an informed decision on how to proceed.

Additives rarely give acceptable results. If there's a real problem, a can of fluid will not help.

If a catalytic converter is blocked on a high mileage engine, the exhaust back-pressure at highway speed can by-pass the rings, over-pressure the oil pan and cause the engine puke oil out the dipstick tube or any openings that are open to the atmosphere.

In 1984, my daughter's 1978 Firebird did that when she was using leaded premium gasoline. The leaded gasoline stopped up the catalytic converter. There was some leaded gasoline still available at the pump in 1984 and was gone completely by 1986.

Ok, what if i just have rings that are just a bit stuck, would an engine flush like restore be helpful and then dump in a premium oil with an oil stabilizer like lucas? just trying to get ideas short of a new engine.

All the additives in the world do one thing, lighten your wallet.
Flushing your worn out engine with a can of snake oil will push it over the edge.
You need to determine the issue by using the info these guys gave you to figure out the EXACT problem. Until then you are throwing money at it blindly.
If you determine the rings are worn and it is blowby (which is almost 100 % gauranteed) you can dump in an oil change and substitute a quart of oil with a can of lucas oil stabilizer . That may help you 'limp " along for a while longer.
Dont expect a miracle though.:spank:

Restore isn't a "flush, per se. It's an oil additive that may or may not give a short term improvement in cylinder/ring seal. I would caution you against using a flush of any sort, anyway. It can cause way more problems than it helps.

I seriously doubt anything from a can or bottle is going to help but if you suspect stuck rings, you might want to try Marvel Mystery oil. Squirt some in the plug holes and use it in the crankcase per the instructions.

In the 1970's, Shaler Rislone worked for me on high mileage engines that had noisy hydraulic lifters and it also reduced smoking exhaust and oil consumption. In 1983, Rislone was reformulated after the introduction of catalytic converters and more stringent emissions controls.

In 2006, the old Shaler Company was sold to Bar's Products and I suspect that Rislone has become nothing but snake-oil. Give Rislone a try, I have not used Rislone in 35 years and I may be wrong about the product.

ok, so what could be reason for this blowby relocating from air/breather to the diptube then? this is confusing.

Combustion forces pressure past stuck or worn rings and pressurizes the oil pan. The excessive oil pan pressure becomes greater than atmospheric pressure and forces oil and oil vapor out of the openings in the oil pan such as breathers and dipstick tubes.

What is an ideal idle for this engine? take into account age(22yrs) and miles(183,000)

Standard idle sped is 650 to 700 RPM in Drive, no matter how much mileage the engine has. If the oil pressure is less than 10 PSI at 700 RPM, it indicates that the engine has worn out main bearings.

The red oil pressure "idiot lights" back in the 1960s were calibrated to illuminate at 7 PSI.