2008 Silverado 5.3 With Tow Package - Safe Transmission Temp?

[metchall]

I just purchased a 2008 Silverado with the 5.3 engine, tow package, and I beleive it has a tranmission cooler, as it has the KNP RPO code. I would like to know what the the real safe temperature range for the transmission is. The book says 180-200, but it will hit 200 towing nothing. When I'm towing my 4,000lb 18foot travel trailer with a light load the transmission will easily go above 200, anthing slighlty uphill and it hits 205-210, any prolonged gradient and it will hit 215 to 225. 225 is the max I have seen, but outdoor temperature is only 65. I'm going to be towing alot with this in the summer adn expect it to be 85 degrees outside.

 

Can someone tell me what a real max temp to pull over and cool it off is?

 

Should i flush the transmission adn change the filter since it hit 225?

 

Should I add something else for cooling this summer? If so do I have to do it at hte dealt not to void my extended warranty?

 

Thanks,

 

Mitch

[dvkillar]

Mitch, I have the same Truck\Powertrain you have. I also see my tranny temp rising above 200 when towing most anything. I have not found a good answer to this yet, but tell me this; Does the truck seem to lose power after it gets over 200 ? mine does.

[Carder09]

Performance tranny oil coolers aren't too expensive if you wanted to swap those out, other than that I think, maybe royal purple may make some additive that keeps your tranny cooler, but im like 48.7% sure lol, it may be another brand or there may not be an additive.

[Stevens03]

I think I've read the fluid starts to break down above 265 degrees. I don't believe you'd ever reach that temp unless you had issues. Your trucks more than capable without upgrading the transmission cooler but if you wanted added security, well it's up to you.

[Doug_Scott]

Since the cooler lines go through the rad as well, I would think the rad cooler is actually a heater since engine temps are generally around 200-220. If the trans temp is 180, it will actually take heat from the rad. Way back in the day, I was told by the guy that trained me on chrylser transmissions (he started with them in '32 at the same dealership we were working at when he trained me to replace him) that an average temp of 215 is normal, and for every 20 degrees above that it will cut trans life in half. That does not mean that if you hit 250 today the trans will grenade tomorrow. He was talking about average temps. If the transmission was driven all the time with the trans at 235, it will last half as long as the trans that is driven at 215 all the time.

These are average temps over the life of the transmissions. And no, running the trans at an average of 100 degrees does not mean it will never fail. Transmission oil temp should be kept over 180 to get all the "good" out of the fluid.

Keep in mind I was told/taught this back in 77. Other than the addition of electronics for shifting instead of a valve body, transmissions have not really changed much since then.

[music]

My normal operating temp range when towing a 7k lb camper (loaded) is approx ambient plus 100F (+/-). Climbing a steep grade is *not* normal operation. Expect to see higher temps during severe/long climbs. The "self protect" mode kicks in around 260 to 270F, iirc... but I've never seen that happen. Later models use Dex-VI fluid, and it will not degrade at these temps like the older stuff could.

 

For reference, I recently spent the better part of an hour climbing a 6 to 8% grade to an elevation of 9700 ft in WY, with camper in tow and family on board. The entire climb was in 2nd @ 40 to 45 mph (with the occasional shift to 1st on steeper sections and/or needing to run slower). The maximum trans temp I saw was 227F, with ambient outside temp @ 45F. It wouldn't have mattered which motor or transmission I had... you wouldn't have wanted to go faster than 40 mph up, or down, that mountain