Re: Don't know which oil to use for tilt/trim
It is very difficult to find a non-detergent motor oil. Neither ATF nor detergent motor oil is appropriate for all systems. BN70 (BUNA rubber - aka nitrile - hardness 70) is the most common material used inside power trim. If the PSI goes much over 1200 then ATF and detergent motor oils can damage the seals.
I use ISO32 hydraulic oil in all systems except 1987-1992 Force. It can be mixed with ATF although it does not neutralize the damaging effects of ATF at higher pressures. It is engineered to maximize life of rubber, to absorb transient moisture, mitigate foaming, and withstand the shearing action of hydraulic pumps. However, some of the older Presolite systems will buck if the oil is too thin. If, after filling with hydraulic oil, the system bucks when lowering then drain s portion of fluid and thicken with 30w non detergent.
Most mercury and evinrude run great with maximized lifespan on straight ISO32 hydraulic oil. HO does have two drawbacks. 1) it costs more. Even in bulk a high grade HO can be $20 a gallon. 2) it is clear and difficult to tell fluid levels when filling.
In a pinch, hydraulic jack oil from auto parts store. It is a cheaper grade HO.
