When should engine fans turn on to cool transmission?

Question

2010 Silverado 1500; automatic transmission; 500,000 km.

I suspect the engine fans are not turning on when they should.

Reason:

When stuck in traffic recently, the truck became sluggish and slammed into gear. It reminded me of when my 2005 Malibu is accidentally put into low gear instead of drive; you can feel the transmission isn't working right/is running hot.

When stuck in traffic or idling, the truck engine stays at 100-105 deg C (good). However, the transmission temperature rises to 90-93 deg C (bad, I think); whereas the normal highway tranny temp is 47 deg C.

Idling:

When should the engine fans turn on? Would they cool the transmission? For example, should the fans turn on when the transmission is above n degrees? When idling, I've only noticed the fans come on occasionally, and only for a few seconds.

For what it's worth, I noticed there is a smaller radiator in front of the main engine rad. I suspect the smaller rad is meant to cool the transmission.

I am a novice.

Answer 1

The engine fans won't turn on to cool the transmission. The transmission fluid is passively cooled in the cooler loop inside the radiator by whatever temp the coolant is at the time. Mind you, this is the coolant temp inside the radiator which will be way cooler than the coolant temps in the engine.

As far as temps for the transmission, at 95° C, you're still in the normal operating range, though getting close to the top. Your transmission shouldn't be in trouble until it's about 120° C or above. If you're worried about how hot it is getting, you may want to get an auxillary transmission cooler for it. They aren't expensive and aren't difficult to install.

As long as your engine isn't overheating, especially in traffic, your fans are most likely kicking on when they are supposed to.