Onan P216 oil cap frustrations

Discussion in 'Mechanic and Repair' started by 75, Jun 2, 2001.

  1. 75

    75 LawnSite Senior Member
    Messages: 992

    The welding machine on my work truck has an Onan gas engine:

    Model # P216G - I/11519H
    Serial # J987814561

    No complaints with starting/reliability/power etc BUT starting to hate the oil cap! It's designed to slide on, turn & lock into place with 2 tabs on the oil dipstick tube. Even new, it wasn't a tight fit - presumably to allow crankcase venting. This was in contrast to an older welding machine we have with (I believe - will check) the same engine - it's cap threads into place securely.

    The old machine still has the cap/dipstick it was delivered with about 6+ years ago. The machines with the newer style cap (we have 3 of them) seem to start out with breaking the dipstick off where they attach to the cap. (Thin metal, 90 degree bend, about 1/32" of material on either side of the hole) Replace cap, few months later same thing :mad: . I think this may be due to the fact that this style of cap vibrates more than the older setup. Gave up on leaving the dipstick attached to the cap - use the new cap with stick to check the oil and the old cap WITHOUT stick while running. Eventually, the plastic cap wears to the point that the tabs don't hold it securely and it can (has) popped off while running :angry: .

    Mounts for engine-to-welder and welder-to-truck appear to be OK and all 3 of our newer machines have done this, I'm wondering if A} anyone else has run into this problem and B} if there is a fix - other than replacement of oil cap every month or so! I wonder if the older style tube/cap can be retrofitted?
  2. sdwally

    sdwally LawnSite Senior Member
    Messages: 386

    We have some of the P216s on sweepers and never had a problem. I'll take a look when I go into work and see what I can find in our parts book. Most of the time the dipsticks tubes are interchangable unless they redesigned the hole. If the hole is threaded you could possible make you own tube and dipstick cap, the hole if threaded should be standard pipe thread.
  3. 75

    75 LawnSite Senior Member
    Messages: 992

    Thank you sdwally - thinking about the problem some more I wonder if it's because the welding machines have the auto-idle feature, where they stay at idle RPM until you strike an arc, then they rev up. In the course of a day's "burning", that adds up to a lot of lo/hi RPM cycles. Plus, the cycle is from idle to full throttle every time. One could leave the engine on the "rabbit" setting constantly, but I think that would likely create more problems.

    I'm hoping the older style tube/cap will interchange - as I mentioned, 6+ years without a problem with that style.
  4. John DiMartino

    John DiMartino LawnSite Silver Member
    Messages: 2,555

    75,I have 3 Onans,all have the threaded assy.My welder has a P218Onan,its a Hobart 8500.Never a problem with the oil cap-Y cant you buy the old style dipstick,and tube,if the lenth are the same?it would fix it once and for all.I have 3 Onan parts engines also,Im pretty sure they all have the threaded dipstick too.
  5. steve

    steve LawnSite Member
    Messages: 98

    Go to your onan dealer and ask for a kit to change the cap over, They had a problem with those. You will get a new cap and use your old dipstick.
  6. sdwally

    sdwally LawnSite Senior Member
    Messages: 386

    You need to check with a dealer. The last message hinted at recall notice on those caps. I did check my parts manual for the P216s, however my manual only goes to I/11313. You engine is diffinetly newer. In my manual they list 11 different caps w/dipsticks and 3 different tubes, all of which slide into a rubber seal at the crankcase. If you want to change tubes and caps you'll need to consult a parts manual that covers your specification number. The specification number designates all the different options available for each engine. The H in your spec number designates that engine has had 8 major manufacturing changes.
    The manual also list an o-ring that goes on the cap. Maybe try a new o-ring or one that has a slightly large diameter. Hope this helps.
  7. 75

    75 LawnSite Senior Member
    Messages: 992

    Yes this does help - and thank you to everyone for the info you've provided.

    8 major manufacturing changes - it ain't never simple, is it? :dizzy:

    I did a search over at the Cummins/Onan etc site & found a couple of places nearby to check with: One is a diesel shop in the same industrial park as my workplace & the other is a truck repair shop one of my friends from the parachute club works at. Small world!

    Armed with the part#, serial # and application (mobile welder) hopefully they will be able to come up with something!

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