Car repair question - flushing the transmission fluid?

Factual Questions
1

I took my car into Midas today for a new muffler/exhaust system. As usual, I brought my car in for one thing only to have more work recommended. The Midas Minion assured me in the gravest of tones that if I didn’t also have my coolant and transmission fluid flushed shortly I was facing an even larger repair bill than the ~$300 extra (!) he wanted to charge for those services (apart from my new exhaust system).

Thanks to the cost of the exhaust system, there was no way I could afford to have anything else done today anyway, but these extra recommendations always make me a bit suspicious. Flushing the coolant is one thing, I’ve had that done before (and probably will anyway once I have some more spare change). But what’s this about flushing the transmission fluid? I’ve never heard of needing to do this; frankly, if it is such a necessity, I can’t see how no other mechanic has ever tried to get me to do it. And although my car is an '89 Corolla with 182K miles, the current transmission has only about 25K miles on it… so how does the transmission fluid get “full of gunk” and desperately need replacement?

Like a lot of people, I suspect, what I know about car mechanics is limited to the extent of work/repairs I’ve had done before. :o So tell me, fellow Dopers, is this something that really needs to be done, or was somebody trying to pull the wool over my eyes?

2

Overtime fluids breakdown,like everything else,They do not preform the functions that they were initally intended to preform.Whether ,or not the mechanic was shineing you on is beyond my knowledge.

3

You do need to have your transmission fluid changed periodically, just like the engine oil (not as often, maybe every 15K miles, check your owner’s manual).

But the transmission flush is I think a relatively new technique where they pump in fresh fluid to force out all the used fluid and sediment under pressure. They use special equipment, so charge a lot more. The theory is that merely draining the fluid doesn’t get all the gunk out. But I have no idea if this really is worth what they charge for it. I had it done once, I think it was about $125. I don’t think I would do it again.

At any rate $300 sounds like way too much, call the Toyota dealer and ask them what they would charge, just for comparison.

4

IMO you were smart to tell the Midas guy to shove it.

I change my transmission fluid & filter about every 25K miles. It’s a surprisingly easy job; the fluid costs about $7 and the filter about $18. Granted, it’s not a “forced flush,” but come on, is that really necessary?

One thing to keep in mind, however, is that simply removing the pan & draining the fluid (which is what I do) does not drain the torque converter. But by changing it every 25K miles eventually most all the fluid gets changed every 50K or so…

5

Here’s what the Car Talk guys say.

I’d get the flush done now, and every so often hereafter. You can get a much better deal than at this Midas, though.

6

I was looking into getting the ‘Power Flush and Fluid Exchange’ done on my car because I had heard some bad things from people about changing their fluid and having contaminants knocked loose causing damage. When you simply drain and refill the tranny you are leaving about 2/3s of the old fluid in there. The flush forces it all out and cleans the transmission out in the process. This is from what I have read and I haven’t seen it done. I talked to a local place about getting mine done but they can’t do it on BMW’s because they use banjo style fittings for their transmissions and the machine won’t work with those.
Here is a site for the place I was looking at. http://bgprod.com/bgconsumer/bgservices/transmission.html

7

First, we assume you do indeed have an automatic transmission. While it’s not a bad idea to change the fluid in manual transmissions about every 60,000 miles, it’s generally not a high-priority maintenance item. And it’s a simple drain and refill, I wouln’t expect it to run more than 50.

Automatic transmission fluid does break down, as it has a very tough job to do. It not only lubricates, it operates the “automatic” devices in the tranny and actually propels the car (fluid drive through the torque converter). The common recomendation is to service it every 30,000 miles, more often if you do a lot of towing or mountain driving. Tranny rebuilders, who spend all day seeing the damage associated with deteriorated fluid, typically service their trannies every 15,000 miles.

The traditional service, which is a partial drain and refill, filter replacement, and pan gasket replacement, has the disadvantage of leaving 1/3 to 1/2 of the old fluid in the system. The flushing service replaces all the fluid, but leaves you with your old filter and old pan gasket. A perfect thing would be to do both, but that’s not cost-effective. A good plan is to alternate–traditional service at 30,000 miles, flushing service at 60,000 miles, etc.

As fluid deteriorates, it typically goes from red to orange to yellow to brown to black, with an increasingly burnt odor. It’s best to change it while it’s still in the red to orange range. Don’t change it if it’s very dark brown or black–often by that point things have gotten so bad that fresh fluid will be the final straw, and it may stop working.

Engine coolant service (flush and fill) is generally recommended every 30,000 miles with traditional (ethylene glycol, but not long-life) antifreeze. An alternative to changing on a mileage basis is to measure the pH of the coolant, but it usually corresponds pretty well with the mileage recommendation.

300 sounds pretty dear for those two services, certainly in my part of the country. I would recommend having the tranny fluid inspected and the engine coolant pH measured by a competent repair shop to see if these services really are due. With 25K on your tranny, I’d be surprised if it were anywhere near the dire state suggested by Midas. But then my experience with the chain operations is that they train their people to sell rather than to have good mechanical judgment, and my belief is that they often oversell.

8

Thanks for the info, folks. It’s okay with me if such things really do need to be done (and that certainly appears to be the case here), it’s just that I hate the feeling that I might be taken for a ride. I’ll get my regular mechanic to deal with this, no doubt more cheaply too!