84 Mercury 90hp I-6 impeller replacement help.

[444]

Edit: Found some instructions that answered my questions on the impellor.


Also, I was going to replace the oil in the lower unit while I'm at it, what kind of oil should I run in there?

 

[emckelvy]

Re: 84 Mercury 90hp I-6 impeller replacement help.

The standard replacement oil would be Marine Grade Hi-Vis gear oil.

If you want to splurge, you could get one of the Premium oils that Merc sells or an aftermarket synthetic.

Either type will keep your gears well-lubed. Theoretically the synthetic may unleash a minuscule amount of hp due to reduced friction.

If you're on a budget, Wal-Mart typically carries aftermarket Hi-Vis oil and also an inexpensive hand pump that screws into the quart bottle. You'll need about 22-24 oz. for a refill.

Note on the drain/refill procedure, always pull the drain plug first then the vent plug. The vacuum formed in the gearcase by leaving the vent plug in prevents the gear oil from rushing out when you pop the drain plug.

Fill from the bottom (drain) until oil gushes out of the vent in a clear stream (no air bubbles). Reinstall the vent plug then the drain.

Note that the motor should be in its normal operating position (tilted down) for the drain/refill.

HTH & enjoy the stinky gear oil (one of my least favorite tasks)!.............ed

 

[444]

Re: 84 Mercury 90hp I-6 impeller replacement help.

Is the lower unit oil basically just a rear diff gear oil like a 75w-90?

 

[emckelvy]

Re: 84 Mercury 90hp I-6 impeller replacement help.

Is the lower unit oil basically just a rear diff gear oil like a 75w-90?

"Basically", but Hi-Vis marine gear oil has additives meant to run in a marine environment. If you get water in the lower unit, the emulsifiers in Hi-Vis gear oil will allow the oil to mix with the water. If you use automotive gear oil, the water will 'stratify' when the motor sits, so you'll have a layer of water sitting right on the propshaft, bearings, and gears where it'll corrode them nicely. The emulsified water/Hi-Vis mix isn't as prone to doing this, since there's at least some oiling value left in the mix.

You can certainly use 75W-90 gear oil in a pinch, but it's worth the few xtra $$$ for the Good Stuff.

IMHO, ed