Transmission Oil

[89Vette]

My flush at the Isuzu dealer was 13 years ago (18K miles). So the fluid is old now. I hear you when you say that it doesn't get "old" but it has been a long time. I know the filter was never changed so I thought at 55K, now would be a good time.

I actually didn't say it never gets old. It does. But it tends to "stabilize" after a period of time (after opening/use). It breaks down a bit (upon initial use) then settles at a longterm weight. But I am talking about normal use.

You make a good point about maintenance schedules. Manufacturers don't make maintenance schedules with collectors in mind. Driving 1k/yr isn't something they normally have in mind. In fact, I would venture to say most vehicles are designed for a 10-20yr lifespan. For example, manufacturer's documentation on the design of the C4 Corvette's FRAME talks about designing it for a 20-yr-lifespan!!! They don't consider you'll keep it for 50+ years....just to look at it.

Owning a collector car (OK two of them) gives me a bit more perspective. Even at my low use level, I don't treat fluids as lasting forever. Somewhere between 5-10yrs would be the maximum I'd let a fluid remain in my car. I think most collectors would lean toward the lower end (5yrs) as a reasonable flush/change interval. I wouldn't disagree. Items exposed to the outdoors visually degrade after 5yrs. OTOH, when sealed/protected, items last much longer. (I'm speaking about cellular decay.)

You should consider changing ALL fluids every few years including brake fluid -- which many never consider. On my 89 Corvette, the manufacturer's guide doesn't list an interval for diff fuild change. Dealers would say never change it. With a 20-yr "shelf life" and/or 200k miles, they might not be wrong. I wouldn't bet on it though....especially when fluid is cheaper than a component overhaul.

Here, the question is about trans fluid. I would categorize our transmissions as sealed since they don't even have a dipstick. As such, I would consider transmission fluid safe for a longer period of time -- but not 13 years. Plus, you wouldn't be spending excessive money on maintenance to swap fluids every 5-10 years! LOL Seriously, lubricants can/do separate/congeal under extreme circumstance. Driving keeps them "mixed". Sitting for long periods does the opposite. With lack of use, lubricants separate and gaskets dry out. Letting a vehicle sit really isn't good for it. Start and drive it every week or two....is something else I recommend you do.

And, what the heck, change fluids every ten years or so -- whether they need it or not! LOL