“Oil level” plug vs “vent” plug on lower unit of 2003 90hp Mercury

[Bird River Dad]

Help a Mercury newbie. Changing lower unit oil and open the drain plug, then open the vent plug above to let it drain faster. Next to the vent plug is yet another plug labeled “oil level”, what’s that about? Please be detailed.

Also, none of the plugs I removed had gaskets. Is that normal for a 2003 4stroke 90hp Mercury ELPT or was previous owner doing a no-no?

 

[QBhoy]

Help a Mercury newbie. Changing lower unit oil and open the drain plug, then open the vent plug above to let it drain faster. Next to the vent plug is yet another plug labeled “oil level”, what’s that about? Please be detailed.

Also, none of the plugs I removed had gaskets. Is that normal for a 2003 4stroke 90hp Mercury ELPT or was previous owner doing a no-no?

Hi. Not that I’m questioning your familiarity at all…but perhaps maybe your eyesight is as mine is these days…are you sure the small seal gasket isn’t stuck in there at the base of the threads ? Usually they stick in there. Can be blue or yellow usually. Normally involves a wee pick with a fine screwdriver to get them out.

 

[Bird River Dad]

You were right, great tip everyone should know otherwise people will install a new washer on top of it. Thanks!

I found out my 2003 is one of the few with 2 vents at top of lower unit.

So weird.

If anyone else has this issue, open both vent plugs (the one on right is named “oil level”) to drain. Refill from bottom drain plug with pump like normal and when it comes out of “vent” -screw in plug and then keep pumping till it comes out of “Oil Level” plug as well which is actually positioned a little lower (weird).