Safe to change Transmission Fluid

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Pulled a 1989 Ski Nautique out of a 5 yr storage and have been cautiously trying to ease it into service.  Pumped out  and replaced all the gas, changed the oil, replaced the cooling impeller (See my other post about cooling system troubleshooting).  Seems to be running OK.  Now I am starting to think about the transmission fluid.  I have no idea when it was last changed.  It certainly is over 5 years old and could well be 10-20 years old.  The boat only has about 500 hrs on it so total run time is probably not an issue (fluids are good for 100,000 miles in a car) but just straight age could.be.   I am all set to pump it out and replace it as the cost is cheap but then I stumble onto a post about how many problems can occur after a change as the gunk/lacquer in the system gets dislocated and clogs up the system especially if you are not changing it regularly.    Boat runs fine.  I don't want to make more problems than I solve.  Thoughts?  
Is there a way to test the fluid?  The color and clarity looks good.  
Does it really deteriorate much just with age?  I am a long way from the natural run-time limit and may never hit it
Is there a compromise - I have seen suggestions to just replace half of it every year assuming you are easing into it 
I have also seen suggestions about performing your own flush by doing two full changes in a row separated by minimal run time - this seems logical but I'd hate to mess up the process (not get all the fluid out etc) as I would be doing it for the first time

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Whitefish1989 Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: June-14-2023 Location: MN Status: Offline Points: 15	Post Options Post Reply Quote Whitefish1989 Report Post Thanks(0) Quote Reply Topic: Safe to change Transmission Fluid Posted: July-16-2023 at 12:57pm
	Pulled a 1989 Ski Nautique out of a 5 yr storage and have been cautiously trying to ease it into service. Pumped out and replaced all the gas, changed the oil, replaced the cooling impeller (See my other post about cooling system troubleshooting). Seems to be running OK. Now I am starting to think about the transmission fluid. I have no idea when it was last changed. It certainly is over 5 years old and could well be 10-20 years old. The boat only has about 500 hrs on it so total run time is probably not an issue (fluids are good for 100,000 miles in a car) but just straight age could.be. I am all set to pump it out and replace it as the cost is cheap but then I stumble onto a post about how many problems can occur after a change as the gunk/lacquer in the system gets dislocated and clogs up the system especially if you are not changing it regularly. Boat runs fine. I don't want to make more problems than I solve. Thoughts? Is there a way to test the fluid? The color and clarity looks good. Does it really deteriorate much just with age? I am a long way from the natural run-time limit and may never hit it Is there a compromise - I have seen suggestions to just replace half of it every year assuming you are easing into it I have also seen suggestions about performing your own flush by doing two full changes in a row separated by minimal run time - this seems logical but I'd hate to mess up the process (not get all the fluid out etc) as I would be doing it for the first time

Jonny Quest Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: August-20-2013 Location: Utah--via Texas Status: Online Points: 2981	Post Options Post Reply Quote Jonny Quest Report Post Thanks(0) Quote Reply Posted: July-16-2023 at 4:23pm
	Change the fluid. I like Valvoline Max multi-vehicle synthetic (gasp!). Easy. Don’t look back. JQ
	Current 2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11125	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: July-16-2023 at 7:23pm
	Since you have an 89 which was the first year of the 1.23 to 1 transmission, do you have Red ATF in there or brownish engine oil In the early years of that transmission, PCM couldn't make up their minds about which to use and they were each recommended at different times, till they settled on ATF (Dexron 3 or an equivalent) Dino or synthetic discussions never have a definite answer. Both work, but PCM recommended dino Changing half of the oil would be like changing half of your engine oil, every other spark plug, wiping half of your butt, brushing half of your teeth etc And what are good numbers or change intervals for a car really mean nothing in a boat. Some people change their fluid every 50 hrs, some every year, some go years and years. PCM says every year And.............how are you gonna get the old oil out? More than one person around here has used a plastic suction tube and broken it off or got it stuck in the transmission. Sometimes they got lucky and fished it out.........some had to take the transmission apart enough to get the tube out. There's a tiny hole inside to get the tube through so you can get all the oil out. You don't wanna be that guy Plastic is a no no

uncle-buck Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: June-14-2004 Location: United States Status: Offline Points: 330	Post Options Post Reply Quote uncle-buck Report Post Thanks(0) Quote Reply Posted: July-21-2023 at 9:44am
	I use a vacuum type oil extractor with thin copper HVAC tubing to evacuate the used fluid. Work it gently and carefully into the trans. housing through the dipstick port.
	1990 Ski Nautique (original owner) PCM 351W with D.U.I.

Safe to change Transmission Fluid

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