Re: Mariner 55el gearbox oil level check.
There may be three plugs. One on the bottom for draining the gearlube, and one on the top as a vent for filling and draining. If there is a third, it is for flushing the cooling system and will be labelled on the casting.<br /><br />To drain the gearcase, crack the vent plug to relieve any pressure in there and snug it back up a bit. Then remove the drain plug and finally remove the vent plug.<br /><br />To fill the gearcase, pump gearlube from the drain hole until it comes out the vent hole, plug the vent, and then plug the drain. If either of the gaskets are damaged, replace both.<br /><br />As far as checking, remove the vent plug ant there should be some lube there. I also like to check at the drain to see if any water has accumulated.<br /><br />You can tell a lot about the condition of the gearcase by the lube that comes out of it. A milky color indicates that water is getting in there. Very black oil is usually the result of age and use, but could indicate a bad bearing if it turns black within a single season. A somewhat metallic look isn't unusual, but a lot of fine metal in the lube could indicate a problem. Naturally bits of metal in the lube would be a bad thing. Many oil drain plugs have magnets on them to attract and hold metal. A fine powdery accumulation is normal. Fine slivers indicate a stainless steel prop or high idle speed. Big chunks mean you'd better tear it down and find the source.
