3rd or OD in the mountains

[Burbski]

I would think with the 4l80 and a relatively low weight trailer, you should be fine most of the time. But wouldn't hurt to drop a gear during a harder climb.

Maybe get a dongle thingy for the OBD2 port and some app to keep track of the trans temps.

As for the winter and a cooler, don't worry about that at all. I'm from the frozen north and one of my trucks has a trans cooler, once it's warmed up, there is no difference from when it's warm out.

Good to know, appreciate the reply.

 

[Burbski]

3K trailer, dont worry about it. Run it in OD... it'll downshift if it needs to. Your drivetrain (not suspension) is built to run a 10,000lb GVW Dually with a bed full of bricks.

If it was a 4L60, I'd say go to 3rd in the hills.

And yea, for any 1996+ truck I'd recommend getting the trans temp app on your phone or tablet just because its so simple.

Thanks

 

[Burbski]

Consider plumbing a cooler through a thermostat.

That's a good idea, thanks

 

[Schurkey]

1996 Suburban 2500 7.4 4L80e

and will be towing a good amount in the mountains this summer. It is a small trailer (~3000 lbs) without trailer brakes.

Do you think I should be towing in 3rd or OD, or a combination depending on the hills vs flat?

PAY ATTENTION to the way the "automatic" transmission operates.

If it can hold the torque converter clutch "ON", you're probably OK in overdrive.

If the torque converter clutch disengages, better to be in 3rd or even 2nd gear with the converter engaged, than a higher gear with the converter unlocked.

I know I should eventually get a trans cooler,

Maybe. Verify your trans temp BEFORE adding another cooler.

Will the cooler have any adverse effects in the winters, it regularly gets below zero where I live?

Consider plumbing a cooler through a thermostat.

Consider plumbing the hot trans fluid through the aftermarket cooler, THEN through the radiator cooler. When it's hot, you have two coolers assuring that the trans temp is not overly-warm. When it's cold, you have the engine heat via the radiator to warm the fluid before it returns to the transmission. Speeds warm-up in the winter, prevents overheating in the summer.

 

[Komet]

Personally I'd drop it into D uphill but you're probably ok in OD on the flats.

Also, I'm a fan of trans coolers with integrated thermostatic bypasses plumbed after the radiator cooler. I might be getting ahead of myself with the science here, but my idea is you want the liquid cooler first because the higher the trans temp, the more it will try to normalize the temps as it passes through the liquid cooler, then the air cooler drops it further before going back in because the trans ideally wants to be slightly cooler than engine operating temp.

And of course, when it's cold the engine coolant warms up the trans fluid and the bypass is active so no further cooling occurs.

 

[Utah York]

I've towed my small car to Denver from Utah and shift to 3rd many times in the mountains. When I see my speed dropping below 55-60mph, I'll drop down to 3rd and get back up to 65mph. Some of them grades are pretty steep and 70mph is not important to me.

 

[Burbski]

PAY ATTENTION to the way the "automatic" transmission operates.

If it can hold the torque converter clutch "ON", you're probably OK in overdrive.

If the torque converter clutch disengages, better to be in 3rd or even 2nd gear with the converter engaged, than a higher gear with the converter unlocked.


Maybe. Verify your trans temp BEFORE adding another cooler.



Consider plumbing the hot trans fluid through the aftermarket cooler, THEN through the radiator cooler. When it's hot, you have two coolers assuring that the trans temp is not overly-warm. When it's cold, you have the engine heat via the radiator to warm the fluid before it returns to the transmission. Speeds warm-up in the winter, prevents overheating in the summer.

Thanks Schurkey - this is great. The suburban is such a great truck for our family and making small upgrades to get many more years of service is waaaay better than buying something new.

 

[Burbski]

Personally I'd drop it into D uphill but you're probably ok in OD on the flats.

Also, I'm a fan of trans coolers with integrated thermostatic bypasses plumbed after the radiator cooler. I might be getting ahead of myself with the science here, but my idea is you want the liquid cooler first because the higher the trans temp, the more it will try to normalize the temps as it passes through the liquid cooler, then the air cooler drops it further before going back in because the trans ideally wants to be slightly cooler than engine operating temp.

And of course, when it's cold the engine coolant warms up the trans fluid and the bypass is active so no further cooling occurs.

Thanks, I unfortunately need to take short trips around town and a little heat in the winter sounds like a good idea

 

[Pinger]

Bearing in mind that there's no heat from the saddle cooler to the trans fluid until the coolant thermostat has opened.

 

[udidwht]

PAY ATTENTION to the way the "automatic" transmission operates.

If it can hold the torque converter clutch "ON", you're probably OK in overdrive.

If the torque converter clutch disengages, better to be in 3rd or even 2nd gear with the converter engaged, than a higher gear with the converter unlocked.


Maybe. Verify your trans temp BEFORE adding another cooler.



Consider plumbing the hot trans fluid through the aftermarket cooler, THEN through the radiator cooler. When it's hot, you have two coolers assuring that the trans temp is not overly-warm. When it's cold, you have the engine heat via the radiator to warm the fluid before it returns to the transmission. Speeds warm-up in the winter, prevents overheating in the summer.

I own a 1994 P-32 Southwind Storm (28ft) 454 TBI w/4L80E trans the max tow weight is ~3500lb, but I do not tow. The weight of the RV combined with it's aerodynamics puts it into a completely different category. I know from my OBD scanner that even when not towing, you're towing. The RV weighs 11,*** unladen then include the aerodynamics of the RV and instances of headwinds, you have increased the tow capacity without even towing. You better be in 'Drive' as opposed to 'OD'. As for the trans line routing the correct routing is the output line from trans goes to the radiator side tank first then to the external cooler then back to the trans. This routing ensures the trans fluid reaches operating temp quickly during winter times. During moderate-warmer climate the fluid will reach operating temp quicker and be cooled further after exiting the radiator side tank and running thru the external cooler prior to returning to trans. (during grade climbs especially). This is how they are routed from GM.

The general rule with a vintage 4L80E class A RV is you are always towing even when not pulling a TOAD. If you hook up a TOAD... you put the selector in 'Drive' as opposed to 'OD'. That vintage RV were an oxymoron to say the least. Even not towing your towing. I quickly realized that when in "OD' the only time you're in OD is on perfect flats. Hit any type of grade (even an overpass) and the trans goes to 3rd. Even a stiff headwind will do it. Now a Suburban may yield different result/s given they don't have the weight and bread-loaf shape of a class A RV. But it would be as close to what one would expect once you pull something in terms of comparing.