Changing Transmission Fluid

I’ve a 2005 Chevy Astro AWD, 78,000 miles with a transmission cooler that I use for camping, towing, hunting, retriever training. While I change the transmission fluid at an increased frequency but I’m inclined to change it more often.

I don’t change the oil myself, but use a mechanic to drop the pan, change the oil, and change the filter. I found out about a device called liquivac that can be inserted into the pan and aspirate out the fluid in the pan. Since that won’t completely change the oil, I could aspirate out 4 quarts, replace with new oild, drive the care, and repeat the cycle for 3 total times to dilute the oil to the extend that only a little of the old oil remains.

How effective do you think this would be to do this between the 15,000 mile transmission fluid changes I already have performed?


The 3 cycle drain is what Honda recommends for the Accord. I also think that your 15,000 mile frequency is twice as often as you need to do it already. 30,000 miles is probably at least twice as often as Chevrolet recommends. The general opinion around here is that 30,000 miles is a good change frequency.

I don’t have an issue with what you’re doing although every 15k miles might be a bit more than necessary. However, if a lot of towing is done then it certainly won’t hurt a bit and the transmission fluid cooler is worth its weight in gold.

My hat is off to you for thinking about the transmission and actually doing something about it.
This forum is littered with questions about trans fluid changes and unfortunately, the majority are related to transmission problems and lack of ever doing a fluid change.

@ok4450 : yes OP is doing a lot more than the average person. However, most cars and trucks have a special drain schedule for towing. This used to be about 15,000 miles, but I don’t know if that is still the case.

On my Toyota, it is 24 months or 20,000 miles for transmission fluid and differential fluid. Regular interval is 72 months or 60,000 miles.

Thanks for everyone’s comments. I Don’t tow that much, about 2600-3000 miles each year. The owner’s manual recommends every 15000 miles for frequent towing. They don’t clarify “frequent” so I’m doing more not less.

I’m not dropping the pan and changing the transmission fluid completely. It’s by gradual dilution. I draw off about 2-3 quarts, and replace it, and repeat this for a total of 3 times. I’ve been performing this and the fluid is a nice red color. I could wait to see how many miles before the fluid becomes black, but then that is too late.

At the 15,000 mile interval, I’m sure the fluid is also red when my mechanic drops the pan. I’d do it myself, but I’ve never seen it done, so I’ll rely on the mechanic.

Your suction pump method removes virtually the same amount of oil as dropping the pan. Half the fluid stays in the torque converter regardless. One thing the pump can’t do is change the filter, so I would be doing that every 60K miles…If you remove the oil first, THEN drop the pan to access the filter, you should be able to do it with little mess…

Vacuuming fluid out is a somewhat tedious process. I believe it would be much less tedious to drop the pan and install a drain plug in the pan so that future service would be quite simple.

Sorry if off base on this, but my tb can only drain 1/2 the fluid unless you crack the case. A neat work around was disconnecting the from trans line at the radiator and dumping into a bucket while pouring new in until all was looking fresh and clean. 12 quarts in my example.


Your pan doesn’t have a drain plug, so draining the fluid can be tedious. I suggest you have your mechanic install one of these. Believe me, you’ll be making future trans services a LOT easier for the guy. He will thank you the next time he can remove the plug and drain the fluid, rather than trying to remove the pan without spilling a bunch of hot fluid.

Look on page 6-7 of this schedule. It seems that you should be doing a trans service every 15K, if it falls under severe service. You are doing the right thing.

And if you want to a drain and refill halfway between services, it’ll be easy with that pan I showed you.

Given your use, once every 15000 is plenty. So doing more won’t hurt I guess. Doesn’t really matter how at that point.

After draining the fluid and dropping the pan, watch out when you unscrew the 3-4 small screws (on a Camry) holding the screen/filter- it is holding back 2 or 3 oz…enough to make a mess if you’re not expecting it…then I like to wipe all the fine metallic paste off the magnets and out of the pan. I’d like to buy 4 more thin magnets - anyone know where to buy them ?

Get some of those super strong small magnet and attach them to the outside of the pan. No way for them to cause a problem that way.

The 4L60E transmission filter is not held in place by screws