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  1. #1
    radio-active's Avatar
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    Oil fill warning in manual

    Does anyone know why the MSX 140 owners manual has a stern warning about not filling the oil tank to the brim?

    Add the recommended oil. Fill to within severalinches of the fill hole opening. NOTE: Do notfill all the way to the opening. Wipe up any spillsimmediately.

    I've asked around here and no one seems to remember -- or I haven't asked the right guys yet.

  2. #2
    Moderator HiPeRcO's Avatar
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    Perhaps because they knew about the crappy design of the level sensor mounting, often known to leak like crazy

  3. #3
    radio-active's Avatar
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    Someone here suggested that as well, but it doesn't make sense. If you fill the oil to within a few inches of the cap, it's already well above the oil sender level -- by at least a foot. What's another few inches? A little more oil in the fill tube isn't going to affect head pressure significantly.

    I'm wondering about the possibility of oil escaping from the cap -- which must be vented to prevent oil tank collapse. Or maybe a concern about oil somehow getting into and blocking that vent, keeping it from operating.

  4. #4
    martincom's Avatar
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    The cap is not vented. There is a vent on top of the tank that consists of a thread in elbow, short length of hose, and a check valve. The elbow to tank threaded connection is also pretty crappy and known to leak. When I have a tank out, I add an O-ring or two to the sender neck, a gear clamp around the tank sender opening boss, and I apply 3M Structural Adhesive around the perimeter of the vent elbow, to seal it.

    Assuming the tank didn't leak, you would not want to fill the oil tank to the brim. Typically, the temperature is quite a bit cooler when filling the oil tank. Factor in hot day in the sun and/or engine operating temperature, the hull interior temp will easily exceed 100F. The oil in the tank will expand with the temp increase and something will have to give. Again, assuming a tight tank, I would speculate the vent check valve would fail, ceasing to be a check valve. Then you would have the oily hull mess that most MSX140s normally have.

  5. #5
    radio-active's Avatar
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    Yes -- that makes sense -- I'd forgotten about the tank vent. The empty space under the cap is basically just an air space for the expanding oil.

    So maybe sealing up the vent elbow isn't a great idea? Maybe a little leak is a good thing. No one likes the oil mess (I probably mopped up a quart when I had my gas tank out of the way), but it's a reasonable trade-off when one considers the alternative.


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