So have an 1994 Aerostar with 42,000 actual miles, a garage queen. Service intervals are always listed in miles driven not time between services.

Specifically the differential oils and the transfer case fluids, on a 20 year old low mileage car should I just change them all anyways? Seems like the oil in the ground is millions of years old and we make the lubes out of them...TIA.

Same question on hoses and thermostat and pcv valves etc...Truck runs fine, hoses look good, thermostat opens and closes. TIA.

BRGDS,

p.

 

You need to remember that the oil in the ground has not synthesized and modified. Plus it is not usually exposed to air/water.

The diffs, trans, PS, ect are open systems that come in contact with moisture/contaminants in the air and odds are they have not been touched. I would flush/replace all fluids with fresh.

As for hoses, it depends on conditions over the past 20 years. Did it sit outside all the that time? The biggest killer of hoses is radical temp changes, chemical contamination, and UV. If it lived all of its life in a garage, then odds are the temps were not radical, and UV was blocked.

PCV and thermostat, if you want to replace them, you can, but those are more wear items then time sensitive. They are cheap items, and again, you can replace for piece of mind.

 

Lube change interval depends mainly on how the rig is used, towing heavy? short distance cold? long distance freeway w. light loads?

I've only used full 100% real synthetic lubes in my Aero since new, Redline. Mobil 1 and Amsoil are good also. Reduces how often it has to be changed, which is not fun in the diffs. Want a quality syn. in the auto tranny, front diff and the differential, they get hot in summer heat.

 

if it is not broken, don't fix it.

 

I agree with Jose, if it is not broken, don't fix it.
I have never changed differential oil or standard transmission oil in any vehicle I've owned. The automatic transmission fluid in my 87 is what was in there when I bought it in 98. Check it every oil change. Doesn't look or smell burnt. Have never changed p/s fluid. Brake fluid will get changed during pad or shoe replacement. Engine oil and filter every 5000 miles, with Pennzoil and these days a Fram filter with the rubber grip (never need a filter wrench). I have never replaced a fuel filter but I buy only top tier name brand gas. I've never changed coolant just to be changing it. I'm picky about the air filter and replace it every other oil change, more often if I think it looks dirty.
Never had a need for a 4 wheel drive, so can't speak to that.
All this assumes normal sane driving, no towing, off roading or racing.
Thermostat either works or it doesn’t.
I'm sure that there are many that will disagree with my service intervals but my 97 has over 220,000 miles and my 87 has over 300,000 miles.
As for the recommended service intervals, I've always believed they were intentionally short to increase the dealer’s maintenance revenue but should be followed (at the dealer if possible) as long as the vehicle is under warranty.

 

as a car collector with 2 old Jags I can say that I am guilty of not following my own advice. too much trouble!

engine oil & filter should be replaced after a long storage, that's it. Then after a few long drives and fillups to burn off the turpentine in the gasoline tank, the cooling system should be flushed and refilled.