# When to change transmission fluid/filter?



## Cats4Nat (Jan 28, 2004)

Hey, we have 1999 Yukon 3.73 with 70,000 miles....just started towing last month. We are thinking to change transmission fluid/filter before big trip in August along with P-tires to LT tires.

Since we are not do-it-yourselfers and will have to have trannie work by 'expert', we wanted to know if this is good time or what time is normal .....GMC book says at 100,000 miles if not hard driving....until we got TT, we towed 1200lb pop-up so it wasnt strained.....now it will be heavier with 25RS-S.

We try to keep up maintance on cars since we dont want any 'trouble'.....our little Subaru is at 152,000 and still running great at 26-28 mpg!

Thanks!
David


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## kjp1969 (Apr 25, 2004)

I'd start with the owners manual recommendations for "hard duty," and then adjust from there, depending on how much you tow and under what conditions.

BTW, they have a "flush" process for changing the tranny fluid where they push out the old and draw in the new through the cooler tubes. This method changes ALL of the fluid, vs just that in the pan. This is the way to go, even if it costs a bit more.

Kevin


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## camping479 (Aug 27, 2003)

I had a local transmission shop flush out and fill the trans with amsoil synthetic atf.

While it was in, they removed the stock trans cooler and replaced it with a Long brand stacked plate transmission fluid cooler. The combination of the synthetic atf and the larger cooler helps the transmission to run much cooler. The hottest it's gotten so far is about 180 which is quite a bit lower than the recommended 200 degree maximum. Seems regular atf starts to break down above 200 degrees. The synthetic can take more heat, but the cooler you can keep the transmission, the better.

They recommended changing the trans fluid every 25k miles or so since we use it to tow.

Mike


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## jgerni (Nov 10, 2003)

I would defiantly change the fluid before your long trip for piece of mind. I changed mine using 16 quarts of Mobile 1 synthetic. It is expensive but since we are really working the transmissions in these Â½ ton vehicles I figured it was worth it. Remember do the full flush torque converter and all.


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## j1mfrog (Jun 6, 2004)

kjp1969 said:


> BTW, they have a "flush" process for changing the tranny fluid





> Kevin
> 
> What does BTW stand for?
> 
> ...


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## California Jim (Dec 11, 2003)

BTW = By The Way.

Without doing any towing you should "Service" your automatic tranny about every 60,000 miles. With towing I would at least cut that in half and maybe more.

I also like the idea of having a full flush done as well. If you just drop the pan and drain it you will only get about half the fluid as about 5-6 quarts is still in the torque converter. I'll do this next time and maybe switch to synthetic as well.


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## j1mfrog (Jun 6, 2004)

Thanks Jim


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## kjp1969 (Apr 25, 2004)

BTW = By the way

Check your manual, my '98 Ford wanted new fluid every 30k.

Kevin


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## JimWilson (Feb 24, 2004)

There's no downside to getting the tranny flushed now. And if you replace the fluid with synthetic -- I'm using Mobil 1 in my truck -- you're doing an even better job.

Bottom line; if you're "into" maintenance like you say then that's all the more reason to do it, sooner then later too.


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