C'mon now, y'all know the trans can't take it! The engine will outlive any automatic trans you bolt on it. Nuff said. How to keep that weak link healthy?!

1. Keep it cool! Trans coolers are your friend. My Bonnie didn't have one, but I got a FACTORY setup from a salvage yard SSE(i)!... run, don't walk to get these parts. (Put a piece of cardboard over it in winter if you have winter if you want to, I don't, but I rejected JCWhitney offerings also, so YMMV).

2. Change the fluid and filter! 25,000 miles?! THAT's a LOT of miles! Change it sooner. But MONITOR it: look at the fluid and SMELL it!. REGULARLY! (Can you distinguish good vs. bad transmission fluid by smell? It's "automobile mechanics 101" ("newbie") level of knowledge.)

3. No scientific proof offered, but: Use at least semi-syn fluid (could hurt alreadly old/damaged/done trannies though: it's not a REPAIR)... this is not "consumer chat"!

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'94 SLE, 169k: Black grill from a '97 (not shown). Raybestos Advanced Technology rotors and pads. Factory trans cooler from an SSEi. Silverstar Ultra high and low beams.

You also need a way to monitor transmission temperature to guard against over-cooling, especially the 98+ crowd with the 4T65. Those run a lot cooler than the 4T60.

I have a cooler, and it remained unhooked for the winter since the transmission never made it past 150* F without the cooler even on 2+ hour highway trips. The summer will see temps around 160 with a cooler.

For fluid, the cheap stuff works just fine. Doesn't have to be semi syn even. Just as long as it's changed regularly. If dropping the pan isn't an option, pumping out the old fluid in the pan and refilling with new works.

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2012 Chevrolet Cruze Eco - Current car

1999 Buick LeSabre Custom - Former car

Learn from the mistakes of others, that way when you mess up you can do so in new and interesting ways.

The 4T65E can run alot hotter than a 4T60 by the way it manages the TCC. 65's burn fluid faster by overmanagement of the controls.

If you get a cooler, get a viscosity controlled thermostatic cooler, not a basic tube/fin like the stock SSEi cooler.

And I agree, a trans temp gauge is a very good idea. Especially if you have a 93 or older that doesn't report trans temp through your scantool.

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Click here for mod list for both cars
93 SSEi, 95 SLE (supercharged) 97 Buick LeSabre Limited
PontiacDad at WCBF '04: Cruise control? That's like surrendering!
Comprehensive guide to troubleshooting, rebuilding, and modifying Eaton Superchargers

I can attest to this. My '06 Grand Prix (4T65E) has a trans temp gauge through the DIC...it's not unusual to see 210-230* during the summer months. That's a bit hotter than I like. In contrast, I never see my '97 SSE (4T60E) get that hot. EVER.

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2005 GXP - White Gold Pearl, no mods...yet.
2000 SSEi - Resurrection in progress. Built L67 w/L32 fuel rail, ported heads, and cam. Camaro front brake system, GXP cluster, and much more in planning.

Yup. The 65 is much harder on fluid. But I'd still put a cooler (proper type and size for your climate) on any FWD auto. Especially one with an almost under-rated trans.

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Click here for mod list for both cars
93 SSEi, 95 SLE (supercharged) 97 Buick LeSabre Limited
PontiacDad at WCBF '04: Cruise control? That's like surrendering!
Comprehensive guide to troubleshooting, rebuilding, and modifying Eaton Superchargers

Agreed a cooler is absolutely necessary in the summer months.

Hottest I've seen my transmission temp go before the cooler is 200 on a blazing hot July day. But in the winter it's rare to see 150 for me without a cooler. Could be my car's an oddball.

With a cooler during the summer the transmission stays between 150 and 180* F.

This is all on cheap-o fluid that I've changed twice in the 30k miles I've had the car. Once when I got it a year ago and once just recently.

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2012 Chevrolet Cruze Eco - Current car

1999 Buick LeSabre Custom - Former car

Learn from the mistakes of others, that way when you mess up you can do so in new and interesting ways.

Cheap stuff works just fine. All Dextron III fluids have to meet certain requirements to be labeled as such.

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Bye Bye:

RIP sandrock

There's no true Dexron-III specification anymore since Dexron-VI came out. So it can be piss in a can they're selling you labeled Dex-III compatible. No specification anymore means anybody can claim anything to meet the now-vanished specification.

That being said, I don't see any manufacturers suddenly changing fluid formulations when they have a perfectly marketable product they've made for year after year with no changes needed. Just because the fluid meets a now-defunct specification doesn't make it any worse.

In short, it's still Dex-III with a different label on the bottle. And it's still fine for all the H-bodies.

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2012 Chevrolet Cruze Eco - Current car

1999 Buick LeSabre Custom - Former car

Learn from the mistakes of others, that way when you mess up you can do so in new and interesting ways.