Fluid change intervals for low mile cars

[wws944]

What are reasonable fluid change intervals for older vehicles that see only limited driving:

For starters, lets assume the following:

* A few hundred miles per year of driving on 'sunny sunday afternoons'.

* Normally garaged.

* Engine oil/filter changed every year or two

* Coolant changed every couple of years (can go 5 with modern orange like DEXCOOL?)

Hopefully the above is not too controversial. What I am really interested in is all the 'other' fluids. In particular, things like:

* Tranny - both auto and manual

* Differential (if it has one. Or in the case of 4WD, two.)

* Brake fluid (assume DOT-3 or DOT-4)

* PS fluid

I know in the case of brake fluid, most conservative folks recommend 1 year for DOT-3, and 2 years for DOT-4. But it seems this is very commonly stretched to 5-10 years or more. (I once had a service advisor at a car dealership tell me that brake fluid was 'good for the life of the car'.) If one lives in a fairly dry climate, it seems to me that 5-10 years on DOT-4 is ok. But in a humid climate might be much closer to the 1-2 year mark?

Also how do the intervals change by going to modern, e.g., synthetic, fluids? For example the newer DEXRON VI vs older DEXRON II or III?

Also, how would the above change depending on the age of the vehicle? Would a 1930s vehicle be different than a 1950s? Or a 1960s from a 1990s?

[Rusty_OToole]

Vehicles after about 1968 have a sealed master cylinder. The kind with the bellows like rubber thing under the cap. They will keep their fluid fresh longer. Other than that I don't know any difference in the brakes.

Cars without oil filters require more frequent oil changes than those with filters.

[Guest Jim_Edwards]

Regardless of the age of the vehicle or the amount of miles driven it is a good idea to change the oil in one infrequently driven every six months. Coolant should be changed every two years regardless of number of miles driven or age of vehicle, and should be of the type specified for the vehicle. For most older vehicles this means Ethylene Glycol based coolant/anti-freeze. Some older vehicles also need water pump lubricant to be added to the coolant.

Automatic transmission fluid is a whole different ball game. If the transmission originally specified TYPE A fluid any variation of Dexron is an appropriate refill when needed (note when needed). If the automaker recommends a particular fluid stick with it as the shift modifiers will probably not be compatible with Dexron, this is particularly true of Ford TYPE F and fluids specified for certain Chrysler vehicles. Flushing of transmissions and filter changes are probably not necessary unless abnormal shifting characteristics are observed.

Most brake systems in older vehicles were designed to function properly with DOT-3 fluid, so stick with it. Never introduce DOT-5 into a system specifying DOT-3. Always be observant for steel lines on an older vehicle that may have developed pin holes or deteriorated rubber lines.

Manual transmissions and differentials follow service manuals for the vehicles for proper level maintenance regardless of vehicle age or miles driven.

Others may have additional recommendations!

Jim

Edited February 14, 2011 by Jim_Edwards (see edit history)

[ted sweet]

why 2 years on coolant?

[junkyardjeff]

I usually change the oil once a year on my vehicles that dont go over 3000 miles a year,I do it in the spring when I get them out after sitting all winter. Had to change the oil in my 55 sunliner twice this year since I put about 3000 miles on it this summer and drove it to Florida in the fall and it needs changed again as that trip put about 3000 miles on it.

[wws944]

Thanks all for the responses!

What I am mostly wondering about at this moment is AT fluid, PS fluid, and diff(s). For example, is 20 years 'too long'? If the manufacturer specified a 30k mile interval on the tranny and the car is only driven, say, 500 miles a year, does that mean the original fluid is good for 60 years?

With respect to engine oils, it seems to me that with the change to unleaded gas, and far better oil formulations (e.g., synthetics) the original recommendations for cars built before the mid-1970s are probably way off. Though on a infrequently driven car, one year is still one year.

[92GTA]

Not at all scientific but....

If I had a car only driven 500 miles per year, I would change the ATF, rear diff, etc. every 10 years no matter what. Brakes I would do every 5 and coolant every 3 or 4. Engine oil has been beat to death so I won't touch that one...

[Guest Jim_Edwards]

why 2 years on coolant?

Ethylene Glycol, the functional ingredient in anti-freeze, tends to breakdown when mixed with water and thus looses its ability to function as a freeze prevention agent with the passage of time. Two years has been established as the critical point for replacement based upon the typical 50/50 mix that maximizes the ability of Ethylene Glycol to retard or prevent freezing in automotive cooling systems. In the most simple of terms anti-freeze looses its ability to provide adequate freeze prevention after two years. It actually begins to slowly degrade the minute it is mixed with water.

Jim

Edited February 15, 2011 by Jim_Edwards (see edit history)

[Guest Jim_Edwards]

Thanks all for the responses!

What I am mostly wondering about at this moment is AT fluid, PS fluid, and diff(s). For example, is 20 years 'too long'? If the manufacturer specified a 30k mile interval on the tranny and the car is only driven, say, 500 miles a year, does that mean the original fluid is good for 60 years?

With respect to engine oils, it seems to me that with the change to unleaded gas, and far better oil formulations (e.g., synthetics) the original recommendations for cars built before the mid-1970s are probably way off. Though on a infrequently driven car, one year is still one year.

I think you may be worrying about things unnecessarily. It is almost assured that before AT fluid would have a shelf or use life issue the darn seals in the transmission will begin leaking and require more than just simple maintenance. Power steering systems having flexible lines and multiple seals that will not last even ten years with even minimal use will also lead to replacement of fluid, often from massive unexpected expulsions. Differentials are typically filled with 80-90 wt. gear oil which is not going to degrade very fast in a closed environment. Again, seal, pinion bearing, wheel bearing, and axle failures may well lead to the need to refill long before the lubricant might begin to separate from age. I have several 50+ year old cars that have never had their differential opened for any reason to my knowledge and have the factory lubricant in them. I'd be more concerned about the lubricant in U-Joints drying out and causing problems before worrying about basically closed systems.

Jim

[Larry Schramm]

Here is a great article on transmission fluid.

http://www.lubegard.com/pdfs/shiftpointersbyWayne&Pat.pdf

[Rusty_OToole]

The 2 year change interval for antifreeze dates back to the sixties. Today's antifreeze lasts much longer. I first noticed in the nineties, working on 10 and 15 year old cars, that the water pumps and coolant passages looked pristine inside even though the cars were worn, had high miles, and obviously had not had their antifreeze changed. How long the antifreeze will last I don't know, but in everyday service it seems to last 10 or 20 years or longer.

By the way they don't use the same ethylene glycol formula anymore. I forget what they changed to but it won't poison small animals.