Compression and oil consumption

[19jacobob93]

Just wondering, say if you had an engine that consumed oil past the rings, would this engine have low compression and blow by to go with it?
If an angine had no abnormal blow by levels and burnt no noticable oil could you presume it had good compression across all cylinders?

My old Mitsubishi 2.6 with 270k (head blew at 299k) burned a lot of oil and smoked like crazy with 20w50 plus Lucas in the sump! That engine also had pretty massive blow by, when you loosened the oil cap with the engine idling it would blow the cap off! If you revved it, putting your hand over the fill hole blew more than putting your hand over the exhaust haha

My Falcon with 210k on it uses virtually zero oil with just 10w30 and at idle no air can be felt coming out of the fill hole at all and only a small amount when revved which is normal in even new engines. Could I presume from this that the Falcon has full/good compression?

 

[spasm3]

You can have stuck oil rings on some model cars and have good compression. For example, saturns. Most but not all saturn s models burn oil. They had low tension rings and no drainback holes in the ringland. The oil bakes in the oil control ringset and they are stuck. Yet most saturns do not smoke, they have good compression and burn the oil clean. My sons s1 now burns a quart in 400 miles, yet it does not smoke.

 

[19jacobob93]

Originally Posted By: spasm3
You can have stuck oil rings on some model cars and have good compression. For example, saturns. Most but not all saturn s models burn oil. They had low tension rings and no drainback holes in the ringland. The oil bakes in the oil control ringset and they are stuck. Yet most saturns do not smoke, they have good compression and burn the oil clean. My sons s1 now burns a quart in 400 miles, yet it does not smoke.

Yeah that would be an exception I didn't think about that!

 

[chrisri]

Originally Posted By: spasm3
You can have stuck oil rings on some model cars and have good compression. For example, saturns. Most but not all saturn s models burn oil. They had low tension rings and no drainback holes in the ringland. The oil bakes in the oil control ringset and they are stuck. Yet most saturns do not smoke, they have good compression and burn the oil clean. My sons s1 now burns a quart in 400 miles, yet it does not smoke.


But I'm sure whole car smells from all that burnt oil

 

[spasm3]

Originally Posted By: chrisri
Originally Posted By: spasm3
You can have stuck oil rings on some model cars and have good compression. For example, saturns. Most but not all saturn s models burn oil. They had low tension rings and no drainback holes in the ringland. The oil bakes in the oil control ringset and they are stuck. Yet most saturns do not smoke, they have good compression and burn the oil clean. My sons s1 now burns a quart in 400 miles, yet it does not smoke.


But I'm sure whole car smells from all that burnt oil

You'd never know it burned oil.
I did just do a 24hr piston soak with berryman b-12 and changed the oil, I'm trying a run of kreen in it to see if it makes a difference. If not its going to get a rebuild with sealed power rings and new pistons or the existing pistons drilled.

 

[Trav]

The piston has 2 different systems working at the same time. On a 3 ring piston (3 piece oil control ring). The top ring is what provides most of the cylinder compression.
The second ring act to help compression somewhat but acts more as a secondary oil control ring.
The oil control ring controls oil from getting up to the compression rings, the oil control ring also holds oil to lubricate the cylinder wall.

If the engine is neglected or oil change intervals too long the oil control rings can get stuck an/or filled with deposits and not work properly.
The top and second rings can remain basically unaffected. So yes you can have good compression/vacuum and leak down readings and still burn oil.

Enter the piston soak.
For lower compression a soak from the piston top will usually work okay, it is less effective on V and H type engines because its hard to soak the whole piston. L engines usually have better results.
For oil burning issues this approach is the least desirable, if the top and second rings are doing their job properly very little of the product used from above will find its way down to the oil ring.

Oil control ring issues are best addressed from below with a product in the oil, it is after all the ring closest to the oil and first in line to receive the cleaning product not the last.

Sorry for the rant, just some thoughts on your question.

 

[Jetronic]

if the valves are burned or the valve seats worn you can have very low compression and no oil consumption.

same thing if the head gasket leaks across cilinders.

 

[circuitsmith]

Originally Posted By: Trav
For lower compression a soak from the piston top will usually work okay, it is less effective on V and H type engines because its hard to soak the whole piston. L engines usually have better results.
For oil burning issues this approach is the least desirable, if the top and second rings are doing their job properly very little of the product used from above will find its way down to the oil ring.

Oil control ring issues are best addressed from below with a product in the oil, it is after all the ring closest to the oil and first in line to receive the cleaning product not the last.


How 'bout this:
1. Remove engine
2. Remove oil pan
3. Flip engine upside down for L, to appropriate angle for V
4. Pour solvent into pockets behind pistons and soak
5. Work the crank back and fourth periodically to shake things up

 

[Trav]

Thats works. LOL But hey your not far from wrong, with a lawnmower you have a much better chance if you stand it upright sand gas and oil so the cylinder is pointing upwards.

 

[spasm3]

Originally Posted By: circuitsmith


How 'bout this:
1. Remove engine
2. Remove oil pan
3. Flip engine upside down for L, to appropriate angle for V
4. Pour solvent into pockets behind pistons and soak
5. Work the crank back and fourth periodically to shake things up


Well i quess you could, but while you have the engine out and upside down and the oil pan off , you might as well slap( I know there is more to doing it right that this) some new bearings and rings in there and be done with it.

 

[Quest]

@ circuitsmith:

sure! by then when you have get that far, why not tear down the whole thing and rebuild it instead?

New bearings, gaskets, new rings, sometimes new pistons, etc. will restore the engine block good as new again for many more miles to come..

And then there's the additional work on the cylinder head part...

Q.

 

[circuitsmith]

Originally Posted By: Quest
@ circuitsmith:

sure! by then when you have get that far, why not tear down the whole thing and rebuild it instead?


Same reason one might pull the engine and put in a used one.
Pulling the head(s) off is a lot more wrenching than lifting out the whole engine.

If I knew there was only gunked up rings and no excessive wear I might consider it.