Questioni have a 1990 chevy pick-up with 218,000 miles on it. the automatic transmission hasn't had anything done to it for at least the last 118,000 that i know of. would it be safe to change the fluid and filter now, or would it harm the tranny? There's nothing wrong with it now, just want to do some preventive maintainence.
thank you
AnswerHi Billy - There are two schools of thought about this, one, that you leave it alone for fear of changing something in the oil and effecting seals in the tranny or something. The other that if you change the oil, you flush the entire system, that fresh oil is the best way to go.
This is something that you will have to decide on your own to do something, or do nothing, because if a problem occurs, then you get to pay.
If it were my truck, I would be flushing the transmission. There are two ways to do this so that ALL of the oil in the tranny is flushed, including the oil in the torque convertor which doesn't get changed in a normal, drop the pan and change the filter sort of maintenance.
A repair shop or dealer can have a machine that hooks up to the cooling lines on the tranny and pushes all of the old oil out and replaces it with new, and does get the torque convertor. This ensures new oil everywhere.
If you are a do-it-yourselfer, and KNOW what you are doing, you can do this with about a dozen quarts of tranny oil and a five gallon pail and a piece of rubber fuel line.
You take the top oil cooler line off, and add the fuel line onto the cooler line and down into the bucket. You have a helper turn the vehicle on (don't take it out of park!) and when the oil flow starts to sputter a bit into the pail, you have the helper shut the truck down. Add whatever amount of oil will bring the tranny back to full and do this again. You continue to pump out and add more in, until the oil looks a nice bright red, usually about 8-12 quarts, depending. Then the last time, you top up to the full, put the cooler line back on and you are finished. This doesn't change your filter which is something you may want to do as well. Make sure you have a certified disposal place take your used oil.
It's a term of some contention between techs for a long time as to what is better, and I don't think anyone really knows. I can only give you an opinion on what I would do, but this is your truck, so you will have to make this decision for you, but now knowing a bit more about what is happening.
I hope that this helps, and if I can be of further help, please feel free to drop me a line.
Automotively yours,
Dean
