Lower unit cleaner

Lime out, its a bathroom cleaner that works great for that.

Hull Brite is also a great product.  It's a dilute acid and cleans it right off.  Available at Walmart and other fine shopping centers.

id just keep my lower unit out of dirty watter............

seriously tho, hull brite. works great on river sludge

tyler

Newer high gloss paints as on Mercs I would not use the acid base bathroom and shower cleaners because it will dull and discolor the finish, older units it works very well.

On the newer paints use Vinager, works very well and is safe.

Vinegar and water mix does a decent job, I use it to get water spots off.  If it is really, really nasty, I use McGuiars Water Spot remover. 

I think most here are assuming you're talking about water spots and or grime from the lake. I'm taking it in a different direction and am assuming you're talking about the hazey grayish build up that froms on the upper leg of the lower unit below the hood cowl and is usually on the back and left side looking forward into the boat.

I assume this as I just last weekend spit shined the old rig and tackled this job. I tried some Mcguires Soap that was included in a boat owners kit and a lot of scrubbing. that got maybe half of it off. I next tried just buffing it out with the buffer as I was already waxing the rest of the boat. that really did n't work howeer I didn't have any rubbing or cleaning compounds, only wax. I then went with a little WD40 and elbow grease and then I rewaxed it. It got probably 90% of it off. If somebody has something better, let me know, this stuff is likea thin film of baked on grease!

One word...Ducky!!!

seriously, just try it. it will take all of it off. and will not hurt your paint.