I just replaced my trim pump reservoir for my drive. I brought my old tank with me. The owner of the boatyard asked why my tank was stained red. I told him from dex /merc transmission fluid He told me not to use that and use motor oil. He didn't have a tank in stock so I went to another Merc parts dealer and bought the reservoir and two Mechanic's were buying parts I asked them and they said the same. Use motor oil. I have been using transmission for years. The paper that came with the reservoir said to use hydraulic/power steering fluid. Isn't power steering fluid Automatic transmission fluid? Now I don't to what use use. Any info is welcome and appreciated. PS, My Tab pumps are the same as my trim pump.

My trim tab pumps said to use 10-30 or 10/40 motor oil.

Mine use Dex/Merc...

Motor oil was the #1 recommended fluid as it has a higher level of lubrication but the ATF has more anti-foaming properties, quicker purging of air in the system and response time (from back in the day with the 2stroke O/B's)

At the end of the day it is a very BASIC hydraulic system - use one oil (and don't mix) and the system works

I have always ran motor oil in mine. That being said, ATF or PS fluid will work fine too. The ATF and PS fluid will move the trim a little faster.

run what your owners manual says. that being said - my manual says:

"Quicksilver Power Trim And Steering Fluid "
orMaintaining Power Trim Pump Oil Level

IMPORTANT: Check the oil level with the sterndrive unit in the full down position.

IMPORTANT: If quicksilver Power Trim and steering fluid is not available, SAE 10W-30 or 10W-40 engine oil can be used in the system.

CAUTION

Avoid pump damage. Vent reservoir pressure by backing out the vent screw two turns after tightening completely. Units without a vent screw have a vented fill cap. Remove the fill neck seal on models without a vent screw.

1. 2.

Raise and lower the sterndrive unit 6 to 10 times to purge air from the system. Check the oil level visually.

Maintain the oil level between the “Max” and “Min” marks on the side of the reservoir. Fill to the bottom lip on the fill neck.

I use 10w30 synthetic since it's easy to get and cheap...

Out drive trim pump or hydraulic trim tabs pump?

If trim tabs, Bennett suggested using ATF fluid in the installation instructions.

I have always been told 10w30 for drives and atf for the tabs.

One of the Mechanics told me ATF lets the pump gears wear and the pump becomes very noisy. Motor oil he said will not do this. Automatic transmissions in autos have a pump, gears and clutches, seals and use ATF and seem to last but do have a filter. They also use ATF in their Power steering pumps so I don't see problem. Maybe having Hydraulic pistons is the difference. I do like the idea that motor oil slows the reaction time. My K tab's use the same type pumps as the drive and react to fast so I'm going to drain my trim pumps ,lines and rams and see it they become more controllable with motor oil. Probably do the same for drive trim. The hydraulic power steering I would think uses ATF because it uses a automotive type steering pump Difference again is Hydraulic rams so do I stay with ATF?

The label on the pump for my K-Plane says that it wants engine oil. The labels on my Mercury trim pumps say that they want Power Trim fluid, which is Type F ATF. It probably doesn't matter, but I feed them what they ask for.