Trim Pump Fluid

peters715

Seaman Apprentice
Joined
Sep 19, 2022
Messages
36
I recently had the joy of tearing apart my 1969 Starcraft Mercruiser 120 in order to replace the trim limit switch. All in all, the tear down was way past due as seals and u-joints needed to be replaced anyway. So in the end it was a good thing.

That said, I had to remove the rams during this project. I did not compress them, leaving the fluid in them well enough alone. In the pump reservoir there appears to be plenty of oil and it is clear, so good there.

Question though is what oil should I use should I need to top off or otherwise replace? The label on the pump states to use Kiekhaefer Formula Number 4-20W Oil, which near as I can tell no longer exists. I can't assume this unit is filled with Kiekhaefer oil.

If I want to go with a new fluid, would I just use a straight 20W? As for flushing, is it as 'simple' as running a lot of new fluid through the system or is a complete disassembly and cleaning of the system required?
 

Scott06

Admiral
Joined
Apr 20, 2014
Messages
6,432
Was my understanding you can use any 20W non detergent oil or something close to it. I think last time I bought a gallon of ISO equivalent jack oil for $15 at auto parts store.

Flushing would depend on how dirty the system is. You can leave the hoses off the cylinders or cracked and bump the pump to get fresh oil there, then run the cylinders up and down.

What I have done is every 5 or so years I suck the reservoir dry with a turkey baster, refill run it up and down a few times, then repeat to completely change out the fluid. You may not be able to do this with one of the older metal reservoir pumps.
 

Scott06

Admiral
Joined
Apr 20, 2014
Messages
6,432
So mixing oils is only an issue if you are switching weights?
I don't think mixing oils unless they are incompatible will be an issue regardless of weights. You have motor oil in there now so just adding slightly diff motor oil will not cause an issue.

Only place I've seen this be an issue is if you are switching DOT3 to DOT 5 brake fluid which is silicone based
 

Alumarine

Captain
Joined
Feb 22, 2005
Messages
3,733
If these were hydraulic pumps used all day long in machinery then the type of oil would matter more.
These pumps get used maybe a minute a day.
I bet you could use olive oil and it would work fine.
My pump is marked 10W30, but like Bondo I use ATF.
I use ATF for identification purposes in case there's a leak.
 

ScottinAZ

Master Chief Petty Officer
Joined
Jun 25, 2009
Messages
831
I just use Prestone power steering fluid. Its clear, and the right weight for the system. no issues.
 
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