ATF. They react faster

Yep mine too. I've used 30w engine oil in all my Merc trim pumps. 30w for the Dana tabs also.

Mercruiser recommends for trim tabs. 10w 30 or 10w 40

http://www.ibs-ny.com/freedom/Engine...Tab%20Pump.pdf

I use 30wt motor oil. If I end up with a pump that's a little slower than another pump I put thinner oil in it. This usually helps to speed it up a little...

I've always used power steering fluid. It's always worked well and reponds quickly. When it comes right down to it I guess you can put in what ever you want. MerCruiser power trim amd steering fluid, 10w30, 10w40, power steering, atf, etc. Use what you have best results with.

For those having motorcycles, Fork Oil @ 15W works great as well too for trim pumps.

That's what I heard. I tried it and didn't really notice a difference.

I ended up putting the Mercruiser power trim fluid in.

I've used ATF in both trim and tabs and never had an issue. I also use ATF for my steering.

I have found you can use either one.(power steering or ATF)..you probably wont notice any difference since they are both hydraulic fluids and both are in the neighborhood of a 20W oil in viscosity depending on who makes it....the advantage ATF has is in the detergents and friction modifiers in the oil to help keep things clean and keep heat buildup down.....Since the trim/tab pumps are not constantly being used like a trans or a power steering pump, its not really required for them....so basically any good hydraulic fluid will work just fine
Oil depending on the weight may slow the pumps down a little...