BESTDOGEVER 218 #1 Posted August 15, 2015 Has anyone ever had to repair or replace the oil bypass valve on an onan p218 I have tried everything I know how to get this thing to stop pouring oil into the air cleaner. From what I've read that is my next step short of giving up. Share this post Link to post Share on other sites
boovuc 1,090 #2 Posted August 16, 2015 Hi Dodge,If cleaning the mesh in the crankcase breather filter didn't help and cleaning up the flapper, which is nothing more than a check valve didn't help, you may have to do a leak-down test on your engine. Valve stem seals, rings, etc when leaking will pressurize the crank case. I'm sure there are a few other issues that can do or imitate the same and some engine guys with more experience than I have will chime in. I suggested looking at the crankcase breather assembly when you have a pressurized crankcase on an Onan because that mesh screen can plug. Especially if the engine oil was overfilled at any time.When it gets fouled, the flapper also gets dirty and if that can't close all the way, you get the same effect.The easy stuff to do first is to clean the mesh filter, clean the flapper/check valve assembly and make sure the oil level isn't too high. (Check the oil with the dipstick fully inserted and screwed in slightly).I know you checked all these. If none of these worked, a would do a leak-down test and the rear cyl is the first one I would check. Share this post Link to post Share on other sites
boomers_influence 106 #3 Posted August 16, 2015 dodgewhat is the spec# of your engine?it will be 5 # and a letter.thank you boomer Share this post Link to post Share on other sites
BESTDOGEVER 218 #4 Posted August 17, 2015 Hi boomer its 10539B Share this post Link to post Share on other sites
BESTDOGEVER 218 #5 Posted August 17, 2015 (edited) Hi boovucI replaced the breather packing and check valve I had the rear head off and checked the valve seats the rings and piston are less than 80 hours old on that cylinder . It runs great but it's suddenly pushing lots of oil into the air cleaner I'm baffled Edited August 17, 2015 by BESTDOGEVER Share this post Link to post Share on other sites
boomers_influence 106 #6 Posted August 17, 2015 dodgeif i understand correctly you replaced the ringsand piston on the # 2 cylinder only??i recommend a leak down test.i believe poss. broken rings.thank you. boomer Share this post Link to post Share on other sites
BESTDOGEVER 218 #7 Posted August 18, 2015 (edited) The piston and rings on #1 were good #2 had the skirt busted when the conn rod broke thanks to p/o neglect I ran it all last summer with no problems I'm thinking that I would check the oil bypass valve first because the volume and pressure of the gases from the vent are not overly high but the amount of oil in it is and I never checked that when I had the engine torn down Edited August 19, 2015 by BESTDOGEVER Share this post Link to post Share on other sites
BESTDOGEVER 218 #8 Posted August 30, 2015 As an update on this I opened up the bypass and blew it out ,reassembled it rechecked the crankcase vent made sure the drains on both sides were clear and so far it's been working properly. My hope is that there was some sort of debris making the bypass stick and for a change I got off cheap. Share this post Link to post Share on other sites
