Compression good, but burns oil on highway

honda
oil
accord

#1

2000 AccordEX, standard, 4cyl. 117K- two recent compression tests were fine, but the car burns 1/2 qt of oil per 100 highway miles. No leaks on ground. Can anyone point to why this would be, and what I could do about it? Thank you.


#2

First, check your PCV system from end to end, not just the valve. Is there any oil in the air intake tubing? If that checks out, Hondas use what is known as a sleeveless alumasil block…The rings ride directly on the aluminum cylinder walls…This process occasionally fails, leading to extreme oil burning…Any past failure of the air filter element or seal that allows dirt and dust into the engine will quickly bring on this problem.


#3

One other possibility would be bad valve seals, which don’t affect compression. If the PCV system turns out not to be the problem I would suspect seals. Are the spark plugs black, maybe oily?


#4

What are the compression numbers? Just wondering because people often post on this forum with allegedly “good” readings which are in actuality, garbage. Even readings purported to be good ones from a shop are often no good.

It’s quite possible to have not only good compression but great compression and still have an oil burner.
The upper compression rings may be fine but the oil control rings (wiper rings they’re commonly called) may be seized in the piston ring lands.

Like valve seals there is no test for the oil rings, unfortunately, and curing the ring problem means an engine overhaul.
(The cause of seized wiper rings is generally any overheating episodes or failure to change the oil on a regular enough basis.)


#5

Yes, Caddyman,the ENTIRE crankcase venting system must be operating correctly. A perfunctory glance at the most obvious pieces is not enough. If the engine is run at highway speed for half an hour and the oil fill cap is removed while the engine is idling and smoke billows out the venting is not adequate.