excess oil consumption

erubin · Post by **erubin** » 25 May 2023, 17:18

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.

Post by **volvolugnut** » 25 May 2023, 18:21

Two things typically cause excess oil consumption - worn rings or oil seal leaks. Oil seal leaks may be more common on these engines.
Do a two part compression test. The first, with all plugs removed, check each cylinder as they are now. The engine does not have to be hot.
The second part of the test is to add about a teaspoon of oil to each cylinder and retest compression for each cylinder. Higher reading the second test indicate ring problems. No change indicates valve seals are leaking.
Good rings should test 130 to 160 PSI.
volvolugnut

erubin · Post by **erubin** » 25 May 2023, 23:23

But if the oil scraper rings are gunked up the compression can be good since the upper compression rings are performing their duty. What if my oil scrapper rings are what is faulty but the compression rings are good? Please note that all the cylinders are showing gunked up plugs. The problem is not with the compression, hence compression rings are fine. Also I dont have high blow by into the crankcase and fuel economy is good.

Post by **volvolugnut** » 26 May 2023, 07:58

Testing gives more information for informed troubleshooting.
volvolugnut

Post by **Krons** » 26 May 2023, 10:48

If compression is good and you suspect gunk on the oil scraper rings you could pull the plugs and give the pistons a soak with a few ounces of Marvel Mystery Oil in each cylinder. Let them soak a day or two then crank the engine without the plugs in to clear whatever is left. Lay a towel over the engine as it’ll be messy. If some MMO gets to the crankcase not a big problem, just check overall oil level before firing it up.

Definitely time for testing and diagnosis.