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2003 chevy trailblazer_lt_ext
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Discussion Starter · #1 ·
I've got an 03 Trailblazer with 5.3L V8, 3.43 gears, 96K miles on the original drive train, and no tow package.

I'd like to tow about 7,000 lb behind it, and had my local transmission shop put in a stacked plate auxiliary cooler. The tech bypassed the radiator completely, so it wouldn't dump freshly cooled transmission fluid into the "hot" radiator before sending it back to the transmission, so now the only thing cooling my transmission is this new cooler.

Is this the best approach, or should I be using both for maximum cooling? I'm thinking it would be better to run the fluid from the torque converter to the radiator, then through the aux cooler, and finally back to the transmission, rather than skipping the radiator completely.

The same tech told me I should tow in overdrive and only downshift to 3rd for the hills, but I'm inclined just to leave it in 3rd and let the engine run a bit faster (~3K vs. ~2K in D) and keep the transmission from shifting so much. Is that a reasonable approach to keep things cool?
 

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2003 gmc envoy_slt
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7,190 Posts
:tiphat Welcome :tiphat Like the old guy said when asked how he handled his incontinence: Depends. It's been discussed here before. Use 3rd gear, specially in hilly areas. IMO it should go through the radiator. If you live and tow in an area that is warm/hot most of the year, run the aux cooler after the radiator. If you live/tow primarily in cool/cold areas, run the aux cooler before the radiator to help get the trans up to operating temp.:m2:
 

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Northwest Chapter
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7,000lbs is too much for your EXT man, sorry but IMO its not safe going over the weight limit.

For the cooler, lots of people including myself put the aftermarket cooler in after the radiator so the fluid goes from the hot trans to the radiator to the aux cooler then back to the trans.

trans->radiator->aux cooler->trans
 

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2003 gmc envoy_slt
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7,000lbs is too much for your EXT man, sorry but IMO its not safe going over the weight limit.

For the cooler, lots of people including myself put the aftermarket cooler in after the radiator so the fluid goes from the hot trans to the radiator to the aux cooler then back to the trans.

trans->radiator->aux cooler->trans
Sorry. I completely missed the 7000 lb weight. That's 1300 to 1400 over the limit. Not a safe situation for stopping.
 

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2003 chevy trailblazer_lt_ext
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Discussion Starter · #5 ·
The owners manual says it can pull that much with 3.73 gears, but not with 3.43 gears. The gearing doesn't come into play when stopping. I've got trailer brakes on the car hauler, and it stops without any trouble, even with a 5,000 lb vehicle on the trailer. I'm mainly concerned about killing the transmission, but don't want to spend the $$$ to regear the axles right now. I only tow maybe once a month, less than 3 hours at a time.
 

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2003 gmc envoy_slt
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The owners manual says it can pull that much with 3.73 gears, but not with 3.43 gears. The gearing doesn't come into play when stopping. I've got trailer brakes on the car hauler, and it stops without any trouble, even with a 5,000 lb vehicle on the trailer. I'm mainly concerned about killing the transmission, but don't want to spend the $$$ to regear the axles right now. I only tow maybe once a month, less than 3 hours at a time.
Good point and good luck.
 

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Northwest Chapter
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The owners manual says it can pull that much with 3.73 gears, but not with 3.43 gears. The gearing doesn't come into play when stopping. I've got trailer brakes on the car hauler, and it stops without any trouble, even with a 5,000 lb vehicle on the trailer. I'm mainly concerned about killing the transmission, but don't want to spend the $$$ to regear the axles right now. I only tow maybe once a month, less than 3 hours at a time.
True but gears do make a difference when accelerating. What happens if you need to accelerate to avoid something and cant? Im playing devils advocate here, I just dont want something to happen is all.

Once a month for 3 hours is actually a pretty decent amount, I like to think I tow a lot but maybe only once a month in the summer.

Id have the shop change your cooler setup to go through the radiator first then to your aux cooler. And get a PCM tune, it will help with power and shifting (wont burn the clutches as it shifts, these shift waaay to slow from the factory). My .02
 

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2003 chevy trailblazer_ls
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1,236 Posts
The tech that installed your cooler screwed up. Always run it through the radiator cooler first, then on to the auxillary cooler and back to the transmission.

Coolers are more efficient when they are liquid to liquid, and you have eliminated the most efficient part of your system.

Your truck will pull that weight -- pull in 3 -- never OD. A fast and simple way to up the gear ratio is to run shorter tires. Instead of a 245-70, try a 225-60 or even a 50 series. As tire diameter drops, the gear ratio climbs (numerically).

I'd also get a weight distributing hitch setup and a brake controller. You will be wanting steeper gears, but for an occaisinal pull, it will work.

Here's a gear/tire calculator. Check out tire diameters versus engine rpm. Look to move your rpm into the red zone for towing.

 
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