: Compression and oil consumption



brmurph
05-26-08, 09:35 AM
I did a compression check the other day trying to diagnose oil consumption of 800 miles per quart on my Northstar. I was suprised how good the numbers where, the lowest pressure after 5 cranks was 180 and the highest was 188 which I thought was outstanding for 135000 miles. Also the first crank pressure was a low of 107 and a high of 118 (not sure exactly what this tells me but I have heard its good to check :-).

So my question is how useful is this info for oil consumption? Seems odd that I am going through so much oil with such good compression. I always figured it was rings causing the problem but after this test I am starting to think that the problem is valve guides (or seals) but I have never heard of a Northstar having problems with valve guides?? I see in my factory manual there is a process to replace the valve stem oil seals without dropping the motor, any chance this would help?

PCV valve is clean (no oil) and I do my WOT treatments, leaks very little.. Car runs great.

Thoughts?

Ranger
05-26-08, 04:47 PM
It most likely IS the rings. Have you read the Technical Archives at the top left of this page. It explains it pretty well.

brmurph
05-26-08, 05:39 PM
I have read most all of the oil consumption post and like you I always thought it was the rings but now I am doubting that as the compression is very good and the WOT treatments have not helped (keeps burning more and more oil).

Thanks Ranger.

Ranger
05-26-08, 06:13 PM
The ring issue is not because of worn rings, but rings stuck in the lands because of carbon build up as explained in the Technical Archives. If WOT has not helped, you may need the decarbonization treatment. I think AJ posted a tutorial on it. Maybe in the Tech Tips section.

brmurph
05-26-08, 08:42 PM
I hear ya but I have not heard of too many people having great success with the decarbonization treatment. I have had other cars that had gummed up rings that WOT did fix the problem (so I know it does help) just not in this case. I guess for so many years I have thought nothing but rings but now I am starting to think maybe thats not the issue (hence the question about what a compression test really tells you :-).. Another intersting thing to note is how clean the top of the pistons were when I had the headgaskets done..

Now that I think about it I have never read a post where oil consumption was fixed or improved other then WOT treatments. I am sure some folks have replaced rings but I don't remember reading about it (except from the guru years ago).

Thanks again Ranger..

krimson_cardnal
05-26-08, 10:30 PM
So my question is how useful is this info for oil consumption? Seems odd that I am going through so much oil with such good compression. I always figured it was rings causing the problem but after this test I am starting to think that the problem is valve guides (or seals) but I have never heard of a Northstar having problems with valve guides?? I see in my factory manual there is a process to replace the valve stem oil seals without dropping the motor, any chance this would help?

Thoughts?

I've wondered about this as well. What would be the indicator of valve guide or stem oil seal failure in a NorthStar? A classic indicator is white/blue smoke at start-up. Never hear of the valve stem/seal issue on a NorthStar, however. Are they that good? K_C

brmurph
02-24-09, 09:02 PM
I have some new information on this old post (still looking for an answer :-). The other day after driving for about 20 minutes my car was left idling for about 5-10 minutes (which I rarely do) after which I turned off the car. About 5 minutes later I started the car and for the first time I had a "very" large cloud of smoke (blueish/white as I recall) and everyone in the car not only saw the smoke screen but also commented on the oil smell, so much it made my nephew a little sick. BTW I have not seen this since but I have also not let me car idle that long.

So now I am convinced more then ever the problem is either valve guides or valve seals. Has anyone ever replaced just the valve seals and if so did it help with oil consumption? Any other information on valve seals vs valve guides?

Thanks!

Submariner409
02-24-09, 09:19 PM
Somewhere in here or Seville, last fall, there was a thread concerning valve seals. Not a common failure, but entirely possible for your 150,000 (?) miles. The rings and lower end on these engines are practically forever, so guides/seals are next suspect. There have also been a couple of threads with worn cam lobes at the same time as bad stem seals.........

Jake, 97EldoCoupe, NX8, will know........"damned motor mounts".......

ELDO GUY
02-25-09, 06:39 PM
You might try AutoRX .I thought I read somewhere where this stuff would take care of the carbon problem in the rings. Although with 135 k on the car I think your into the 2 treatment catagory so it would take awhile befor you would see results.

SupRNatural
02-25-09, 08:38 PM
:hmm: I too have noticed a puff of black/blue smoke after a WOT deceleration and flashing the throttle in the driveway. I too have the losing a qt every 700-1000 miles syndrome. I also have a leak undetermined although Sub told me to look in to the O rings on the oil filter adapter. 1 Point. I removed the MAF and took a look see. The whole inside of the intake manifold is loaded with carbon build up (The guy who owned this car was an older gent:yawn::shhh:). Is it advantageous to try and go in there? Is there any decent non evasive maneuver for carbon removal, or just leave it be? @ idle no smoke is noticeable

I really like my car, almost enough that if it needed a new engine I would put one in.:rolleyes: I believe I'm not anywhere near that with only 107K on the clock, and it still pulls hard with no real loss of power. I too have WOT this baby to see no changes.:rant2::yawn:

Ranger
02-25-09, 09:07 PM
Is it advantageous to try and go in there? Is there any decent non evasive maneuver for carbon removal, or just leave it be?
Yes, cleaning it is regular maintenance. I think it is called for every 30K. I do all my cars every spring. That makes them pretty easy because there is no real build up. Use TB Cleaner.

JohnnyO
03-12-09, 10:49 AM
Pre-2000 N*s simply burn oil. On the '99 we've had the dealer do the decarbonization, have run Auto-RX in it (which is a good thing to do anyway), nothing makes any difference. Cadillac will tell you that burning a quart every 1000 miles is "normal". The ONLY thing I've found that slows it down is using Valvoline's Max Life oil. Just change it with Max Life, put in 7 quarts not 7.5, add more when the low oil light comes on, change it when the OLM runs out, and don't worry about it. It is what it is.
Meanwhile our '04 never burns a drop.