2004 3.5L using oil, do I have low compression??

[sagacious]

Guys/Gals,

I have a 2004 Vue with the 3.5L V6 @ 178,000 miles and I've noticed that it's consuming oil in between oil changes. I have no idea how long it's been doing it since my wife used to drive it all the time but I did make sure the oil was always changed every 3k miles since we bought it used at 72,000 miles.

Anyway, since I just noticed this I don't know how quickly it's using oil yet but I'll start tracking it. So, my question is pretty generic at this point. Is there any other possible cause for oil loss besides low compression? I've already replaced the PCV valve and I don't see any visible oil leaks. I also don't see any engine oil contamination in my coolant or transmission fluid.

So, I topped off the oil yesterday and went driving around to let it warm up and then I floored it while looking in my rear view mirror to check for any white/blue smoke. I didn't see anything visible until sometime after the VTEC has already kicked in, maybe around the 5,500-6,000rpm mark...at that point just before it shifted I saw a white puff that dissipated pretty quickly.

so, I am fairly concerned about worn piston rings at this point but I've been watching my short term and long term fuel trims and I should be able to tell from that, right? Because... if I had a low compression issue, there would be excess raw hydrocarbon in the exhaust system and the O2 sensor would read this as rich and the computer will lean out the mixture (causing negative fuel trim) to compensate. However, I don't have negative fuel trims. My Short term fuel trims stay positive in the 1-3% range and my Long term fuel trim stays in the positive from 0-1.6%. Any ideas what's going on??

[SL2 Ride]

I don't follow the oil loss being because of low compression.

[sagacious]

Originally Posted by SL2 Ride

I don't follow the oil loss being because of low compression.

Because when you have low compression the oil can easily slip past the piston rings and get burnt in the combustion chamber...

[fdryer]

Whether or not anyone can determine oil consumption based on stft/ltft is debatable. One site describing how stft/ltft may help; https://www.autoserviceprofessional....for-you?Page=3. If you notice after reading thru all three pages, no mention is made of oil consumption issues. Observing tail pipe exhaust is one of several ways to determine if oil is being consumed in combustion chambers but doesn't tell you if this is valve seal leakage or piston ring wear. White smoke indicates steam, moisture turned into steam from humidity in the air since water doesn't combust. Condensation from overnight cooling is boiled as the exhaust system heats up, seen more in winter temps. Some questions need to be asked and may point to either normal or the beginnings of oil consumption issues.

If you search threads, you may come across periodic valve adjustments due to certain issues. If there's concern about possible compression issues, the best way to determine compression is with a compression gauge. Loaners from AutoZone make it less costly for one time use without buying it. Diagnosing problems can require mechanical as well as electronics knowledge since all EFI engines still use mechanical fundamentals for timing, compression, oil pressure, etc. Not everything can be determined solely from reading OBD II displays.

[SL2 Ride]

Originally Posted by sagacious

Because when you have low compression the oil can easily slip past the piston rings and get burnt in the combustion chamber...

but it's high compression that does that, not low compression.