07 GP GXP 5.3 v8 4t65-e. Monitoring temps of my fluid I am seeing 190-225 degrees consistently each trip no matter the traffic. Does anyone know the expected normal temperature ranges the Trans fluid will be during normal operation? After seeing many recommendations to add a Trans fluid cooler which are the better built brands or model names of coolers? Which cooler unit stand alone or online with radiator would be most labor intensive to install? Thank you .

If the temp was too high, it would set a Transmission code......naturally, in summer, temps will be higher than winter.....how are you reading the temps, though the DIC?

How often do you change the fluid/filter?

I had been keeping my eye on the DIC and observing temps over the course of 2 weeks. The transmission had been rebuilt the oil and filters changed during that time. I bought this car with 75,314 miles and it'* now has 76,458 . the dealer had car and drove it about 800 miles after the rebuild. I have no idea what it'* symptoms where previous to its transmission failer. I would like to avoid having it get so hot it throws a code. Thought I would simply inquire here about the operating temps and what is normal. I want to add the cooler to prevent future trouble.

To my way of thinking you can do one of two things, either add an aftermarket trans cooler or do frequent transmission fluid and filter changes, kinda depends on your driving style and more importantly if you have extreme elevation changes. I live in the low country of SC now where it'* flat for 95% of the 151,000 miles that my wife and I have put on the Bonneville. Except for a couple of excursions into the blue ridge mtns it'* been a flat land car. From what I've read you can expect about 50,000 miles out of transmission fluid at a constant 195 degree operating temperature. Since you can only replace 55% of the transmission fluid in a 4t65-e with a pan drop, I generally change the fluid and filter every 30,000 miles or so, and if I'm feeling particulary trans paranoid I'll pump out about 6 quarts thru the dipstick tube between pan drops. This service schedule has worked so far, I've used Dex VI since it became available I think in 2006. I did install the trans-go shift kit at 140,000 miles to address the hard shift problem, worked like a charm. So at 151,000 miles on my 4t65-e maybe I'm living on borrowed time, but it'* performing like a trooper for now. I had mentioned elevation change earlier for this reason, back in 2007 I was visiting my home state of Wa. and had a rental GP that had trans temp in the DIC which my 2004 Bonneville doesn't. This was in July and from Seattle, basically at sea level, to the summit of Stevens Pass at 4000' elevation, the trans temp climbed to 255, at that temp the fluid is only good for about another 5000 miles. Whether or not you add a cooler, next time you do a pan drop fluid and filter change, throw out that little rectangular magnet and use 2 of those large donut shaped magnets, the little rectangular magnet was totally inadequate, there was a tsb about it.

2004 Bonne SLE
1971 Chevelle SS

Thanks kindly for your reply.. do you have a recommendation for model/ brand of is free market inine Trans cooler ? Thank you

Sorry typo * brand or model of after market inline Trans fluid cooler.

Hayden is the big name in transmission coolers, but Tru-cool has an interesting line-up of coolers too. If you live in a mountainous region of the country, an auxiliary transmission cooler would be the way to go.

2004 Bonne SLE
1971 Chevelle SS

True cool is my choice ..thank you