Brangeta

I created a "How to Install a Transmission Cooler on a 2005-2008 Pontiac Grand Prix GXP" website that gives a step-by-step guide with photos, diagrams, and written instructions on how to do the entire process. https://sites.google.com/view/grand-...grand-prix-gxp I have parts and tools lists on there as well, with links for where to buy everything. I created this because I was sooooo annoyed I couldn't find a guide online that I thought was useful or well done. What few still exist are incomplete... missing photos... full of dead links... or for custom transmission coolers you can't even buy from TEP anymore. This guide should be useful for Impala SS, Monte Carlo SS, or Buick LaCrosse Super and for people with 2004-2008 3800 V6 Grand Prix cars too, but it's specifically for a Grand Prix GXP. I installed mine in standalone configuration.

breakmyfootoff

Awesome! Thanks very much.

ozias

Hi,
I wanted to thank you for putting togeather the GXP Transmission cooler instructions.I used some of your ideas and some of mine. I chose to use AN line and fittings and i ran all new hose and fittings from the transmission to the cooler. I have a question about the noise have only in manual mode in 1st gear. I have the same thing and cannot figure out why the transmission line is vibrating as bad as it does. It seems like the noise/vibration is coming from where the line is connected to the transmission and vibrates all the way to the cooler. I am curious if you ever figured out why the line vibrates like it does. If i come across a fix for this i will pass it on.

Ozias
2005 Grand Prix GXP

Brangeta

I never fully figured that out in a 100% factual way.

I did, however, end up having the forward apply band breaking a piece off inside my transmission around September of 2022. That caused my transmission to fail. I lost 1st gear on the way to work, and by the time I got to work, I lost 2nd as well. Once I got in the parking garage at work, parked, went to work, and came out to go home, I lost all forward gears and had to get towed. Thankfully I was able to roll out of the parking garage, but I didn't make it past the first stop sign. Reverse was all that worked. When the transmission pan was taken off at the dealership, the technician found a piece of the forward apply band stuck to the magnet in the pan. The quotes I got for replacing the trans ($4k to $6k) were more than I wanted to deal with, so I sold the car to someone looking for a GXP instead of fixing it, and bought a 2023 car. To my knowledge, the buyer put his wrecked GXP's transmission in my car and is likely driving it around south Texas now. I've never texted him and asked, because I don't actually want to know. It's not my car anymore.

It didn't fail due to heat or due to transmission cooler plumbing though. It was due to a not-so-strong transmission in a ~84k mile GXP that was driven nearly entirely stop-and-go, red light to red light, stop sign to stop sign its entire life. I didn't drag race it and never did a burn out, but I do accelerate quicker than most people, and it was ready to break. Yet sadly, it did not fail under aggressive driving. It didn't go out in a blaze of glory. I was just driving as normal in 2nd gear approaching a light outside my neighborhood when I heard POP! Clang, clang and I had to drive to work entirely in 2nd and 3rd gears.

When I started to be able to hear the rattling in park, I should have gone ahead and had the transmission diagnosed, because I should have recognized that the noise was not normal and not just in first gear anymore. I had noticed it sounded like a coat hanger in a clothes dryer one day when I stepped out of my GXP to put a letter in a mailbox a few days before the transmission failed. However, I was unsure what it was, was busy with work and grad school, and did not want to spend $100s at the dealership having the transmission pulled in the middle of all that.

If your car is making the noise in park, I'd recommend you do what I didn't do, and get it diagnosed at a dealership or transmission shop before something catastrophic happens.

If your car is making the noise in only first gear, I'm not sure what it is. Maybe the new plumbing just makes it even more obvious that the forward apply band is about to break...? Or maybe it's just a rattle and unrelated. I never fully figured it out. All I do know is that my transmission did not fail due to heat. It failed due to being an old car that had accelerated hundreds of thousands of times from stop signs and red lights.