2018 Silverado 1500 External Transmission Cooler?

Jon A · August 14, 2018

You can tune the fans with HP Tuners, https://www.hptuners.com/product/mpvi2/ . However, it really shouldn't be needed in your case (with that sized trailer, highway towing with no mountains) and probably not worth the possible warranty issues of a tune just for that, unless of course you just want to. Your truck really should be fine as is, I'd expect max temps around 200 degrees, maybe a bit more. I do believe such temps with modern fluids are nothing to worry about--but don't like it getting much hotter than that.

However, there's nothing wrong with lower temps and it can give you a lot of peace of mind to stay way, way out of the danger zone. If you want to do that, all you need to do is bypass the stock thermostat which can basically be done for free. Your stock cooler is big enough it's capable of keeping the temps much cooler, especially on the highway. I usually do recommend adding an aftermarket thermostat as well, but in the south as you are it's not a real high priority and is a lot more work, you could just run with the stock bypassed for a while and see if you feel it's needed.

I'm currently running an aftermarket 140 degree thermostat using the air/oil condenser cooler only, and that setup has dropped my average temps 30-40 degrees from stock in light to moderate use on the highway. I haven't done any heavy towing torture tests yet, just some light towing, I expect during heavy towing the advantage to be greatly reduced but still beneficial most of the time. I'll be hauling a pretty heavy load over some big mountain passes in a couple of weeks so I'll have more insight on how the setup does in those conditions soon.

BillNC · November 1, 2018

With lots of towing, transmission temp has never gotten over 170.

WilliamBos · May 7, 2020

On 8/13/2018 at 4:35 PM, Jon A said:

Yup, that IS your auxiliary cooler. It's actually quite big for a 1500. You have the best transmission cooling available on these trucks. You'll be fine. If you find you want even cooler temps, bypassing/replacing the thermostat with an aftermarket unit makes a big difference and tuning the fans to come on earlier helps as well, especially at low speeds but I doubt you'll find any of that necessary with a trailer that size. Is most of your towing on the highway or is a lot of it on slow gravel roads, etc?

Thanks for posting that parts diagram. I did not know they did that. It's likely the main reason some users of newer trucks have reported better performance (cooler transmission temps) than the older ones. If I had posted my rants on how dumb it was for GM to put an in-tank heat exchanger in the hot side of the radiator a couple of years ago, I might accuse GM of listening to me. Again, so there's no confusion, it's no loss. I have mine bypassed and the trans runs cooler for it. In all but very rare conditions, that radiator tank exchanger acts as a heater, not a cooler. And since we have a thermostat, the heating function is worthless at warmup anyway making it pretty much worthless all the time.

Did these changes happen for MY14? Interesting and great ideas. Is the in tank exchanged on the drivers side of the rad? Need to go have a look at my truck once it stops raining.

CWBB · July 19, 2021

On 8/14/2018 at 2:38 PM, Jon A said:

You can tune the fans with HP Tuners, https://www.hptuners.com/product/mpvi2/ . However, it really shouldn't be needed in your case (with that sized trailer, highway towing with no mountains) and probably not worth the possible warranty issues of a tune just for that, unless of course you just want to. Your truck really should be fine as is, I'd expect max temps around 200 degrees, maybe a bit more. I do believe such temps with modern fluids are nothing to worry about--but don't like it getting much hotter than that.

However, there's nothing wrong with lower temps and it can give you a lot of peace of mind to stay way, way out of the danger zone. If you want to do that, all you need to do is bypass the stock thermostat which can basically be done for free. Your stock cooler is big enough it's capable of keeping the temps much cooler, especially on the highway. I usually do recommend adding an aftermarket thermostat as well, but in the south as you are it's not a real high priority and is a lot more work, you could just run with the stock bypassed for a while and see if you feel it's needed.

I'm currently running an aftermarket 140 degree thermostat using the air/oil condenser cooler only, and that setup has dropped my average temps 30-40 degrees from stock in light to moderate use on the highway. I haven't done any heavy towing torture tests yet, just some light towing, I expect during heavy towing the advantage to be greatly reduced but still beneficial most of the time. I'll be hauling a pretty heavy load over some big mountain passes in a couple of weeks so I'll have more insight on how the setup does in those conditions soon.

Hi there, I was planning on putting a plate/fin after market cooler inline to add some additional cooling. Can you give me some more information (link if possible) on how you bypass the stock thermostat? Or adding and aftermarket? I have a 2018 sierra 1500 5.3 L. thanks for any help.