I own a 2007 Volvo S40 2.4I, engine B5244S7. It as 140k miles. I'm second owner since 100k miles. It's a gas, not diesel engine. I'm consuming up to 1 quart of oil every 500 miles. When I first got it it was 1 qt every 1000 miles. Car is dry, no leaks. I replaced the oil trap PCV but no improvement. All the spark plugs are equally fowled with black sticky residue so I know oil is burning. I've inspected for leaking valve stem seal by reving from cold start as well as idle to rev when hot but no smoke at all with me at the tailpipe while helper is in the car. I've driven at night on freeway to check for smoke in rear view mirror against headlight of car behind me and again no smoke observed.

My guess is oil burning continuously cause oil getting past the rings. What do you think? I dont believe this model year engine had the problematic oil scraper rings.

What should I do? Maybe the oil scraper rings are clogged? Should I try cleaning the rings by introducing solvent into the air intake (careful not to hydraulock). Or put some trans fluid or other solvent in the motor oil and run engine before performing an oil change?

I have a little cheap borescope camera that hooks up to my iphone. Inspect cylinder walls through the spark plug holes? Perform a a compression test or leak down test? Compression seems ok from the seat of my pants.

 

No responses. Anyone have a suggestion where I should post my question?

 

This is fine. I've been on a road trip, and didn't have access to my "real computer" until now...

I did see an interesting approach to freeing stuck oil ring(s) which could apply to your car (or not). But it's cheap and easy, and (if was my S40) worth a shot (IMHO, YMMV).

The process is to pour a couple ounces of Seafoam into each cylinder through the spark plug holes (leaving the plugs out, of course). Let it soak a couple hours, then rotate the engine by hand a bit and wait a couple more hours, then repeat. Apparently, the Seafoam migrates down to the ring, and the solvent action can free it up (or loosen the gunk causing the problem enough that the first drive will dislodge it).

Don't put TOO much liquid (of any type) in the cylinders, to prevent hydrolock. A really quick thumbnail calculation suggests that you COULD hydrolock a 2.4 liter 5 cylinder engine with 2 ounces of fluid (assuming a 10/1 compression ratio). So either use about one ounce of Seafoam, or pack a shop towel over the top of the engine and hit the starter for a couple seconds (which will blast out the majority of the fluid). That said, I suspect enough would evaporate over the 12 - 24 hours that you should use for this process that it won't matter one way or the other.

 

Sounds like a plan. What about adding a solvent (e.g. a 1/2 - 1 quart of trans fluid or some over the counter oil treatment) to the oil about 100 miles before oil change is due. Of corse making sure not to overfill the oil.

Any value doing a compression test while I have the plenum off and the spark plugs removed in order to pour in a bit of seafoam?

And finally should I squirt a bit of oil into each spark plug hole and rotate by hand so the rings dont score the cylinder wall on start up after flushing with seafoam?

 

that's basically what Seafoam is - an oil with loads of detergents - ATF does a similar job where old school mechanics would run an engine with some ATF to help clean out gunk. Sure you can do a compression test prior to doing the detergent treatment as a baseline but keep in mind a compression test after will be skewed by oil being washed off the walls (unless you drive the car for a bit after the treatment then retest).

 

I wouldn't hesitate to use something like Marvel Mystery Oil (or I suppose tranny fluid) though I might not want to drive quite as far as 100 miles before changing the oil).

And yeah, doing a compression test is a good idea (getting a before / after compression test is even better, if you follow mt6127's advice about driving a little prior to the after test).

And finally, I wouldn't worry about scoring the cylinder walls, but a little oil in each cylinder prior to starting up after the Seafoam soak can't be a bad idea.

 

So I went ahead and did the following:
Removed the 5 plugs (2.4L normal aspiration engine). Plugs only have 3k miles on them but they are already showing the start of carbon fouling. Not surprising as I'm burning over 1 qt every 600 miles.
Compression test 1-5 163, 165, 95, 160,165 psi. The #3 with low compression put in oil went to 163. Inspection of piston top and plug is not visually different than other cylinders. After 24 hour seafoam soak #3 went to 100, after oiling it went to 145psi. I wire wheel cleaned all the plugs. Added 7 ounces of seafoam to oil. Let idle for 15 minutes. Took car out for a a nice high rev drive. As always did not see oil burning out the tailpipe at idle, cold start or high speed. Leads me to believe its a steady oil burning past the oil scraper rings. I will perform an oil change in 100-300 miles. After that will monitor oil consumption to see if improved. BTW, I really cant do a compression test on a hot engine because I need to take off the plenum and it's a pain to put everything back together, get to operating temp and then take it all off quickly so engine doesn't cool, hence compression tests were all done with a cold engine.

Next (unrelated?) problem:
My long term fuel trim is almost -20% at idle. At higher rev it comes much closer to 0%. Scan of engine temp is correct. Air filter is clean. I did some scans of the MAF. Here are some snap shots at 3000, 1400 and 700 rpm. Is my MAF correct at these rpms? Why is my long term trim so far negative at idle?

 

I'm concerned that my post is getting a bit too technical. Does anyone know where I can post this for technical mechanics to help me? Thanks in advance!

 

This may not be the site that gets into this level of technical issues but I'll share my solution for the fuel trim problem I have. The brake booster is fed through an octopus assembly of vacuum lines. One line is attached to the plenum (downstream from the MAF). It is a controlled venturi "leak" and provides a continuous known air leak that is designed into the MAF map. At idle this controlled air "leak" is needed. My vacuum line was clogged, no vacuum felt at the air box end of the vacuum octopus so the ECU was compensating for this lack of air by leaning out my trim (large negative value) at idle. At higher rpm regimes the trim levels approach 0 because the air "leak" is a smaller percentage of the air coming in downstream from the MAF. I'm picking up a new hose, PN 31201430. Pretty certain this will fix my negative long term trim. Maybe this will help someone else out there. Especially if they get a OBDII code P0172, system too rich. That code along with LT trims that :fix" at higher RPMs can be due to a clogged brake booster vacuum line. Other cause of too rich could be a dirty/clogged air filter but LT trim will not improve at higher rpms in that case.