678 Universal Rapid-Cool 9.5” x 11” Add-On Transmission Cooler – Not for Direct Replacement of the OE Cooler

First of all, the quality of the radiator itself is very very solid and well made. The heat sink fins are not too thin like many other aftermarket coolers. It’s very well made, and I’ve always had great luck with Hayden products, like their fan clutches, and transmission fittings. I originally bought a Chinese knockoff 40k trucool transmission cooler and I had to return it even before I even put it in my truck because of how poor the thickness of the radiator fins were. I could literally bend them with my finger nails. Did not feel comfortable about putting it in my truck. It was a massive leak waiting to happen. So I bought this Hayden cooler. It was actually cheaper than the 40k knockoff, and it’s much stronger and better built. I will be installing this tomorrow. EDIT: I installed these 2 days ago. Install was very easy, it look me about 3-4 hours because of all the custom mounting brackets I made, and all the hose routing with protective looms on it. But install was very easy and straightforward. I’ve been driving for the past two days with my scan tool hooked up to monitor the transmission temp, and I’m very happy to see that my transmission temperature does not go above 165F, even in slow stop and go traffic. Before I installed the cooler, my transmission temperature temp used to be around 190F-200F, but I’m glad to see how much cooler it is after the install. Very happy with the results, and this modification will definitely make my transmission last much longer.

After Rebuilding my BAYA V6 transmission on my 7th Gen Accord, I needed something to keep the transmission cool since it does not have a transmission fluid cooler. This has kepty transmission happy and was very easy to install. It is an incredible value for the price and looks great once installed. As you can (or can't) see from the photo: the cooler fits perfectly with very little modification and blends in with the radiator. I installed it onto the frame and not the radiator to allow for better airflow. The finished fitment of the cooler was easy and very compatible within the area I installed it. The size is perfect for cooling and quick installation! Highly recommend this cooler setup from Hayden Automotive!

Great item, working good so far. Install on XJ as extra transmission cooler and so far satisfied.

After reviewing many after market transmission coolers, I settled on Hayden and I'm glad I did. The install was simple enough. Drawbacks are the hose it came with (needed to order another) and the aluminum fitting is crap; I ordered a brass type from Hayden. The Install was pretty easy. Make certain you use compressed air to blow out the inside of the cooler. I ran ATF through it as well. I fabricated some simple brackets that I fastened to the radiator frame and then bolted the cooler up to it. Temperature dropped immediately, used to run at 190deg now it runs at about 150deg. Can't even tell it is there bc it is black and blends in with the truck radiator. Would buy again!

Good quality product installed on a 2011 Acura MDX. I followed the video installation guide for the MDX provided by a well-known internet trailer company but they used another manufacturer's transmission cooler. I used the Hayden because I put a Hayden on my last car and had thousands of trouble-free miles with it -- plus, it was significantly cheaper and virtually identical. Here are some notes for anyone else looking to install the Hayden 678 on a 2nd generation MDX (probably also applies to Honda Pilot but not sure): -When I installed the provided hose on the cooler hose barbs, the first one slid on effortlessly but the second was a battle, even with silicone lubricant. I fought it for about 30 minutes and still couldn't get it to seat all the way down. I ended up cutting about 3" from the hose and then it slid on perfectly. I examined the interior of the cut section and it didn't have any flaws. I can't understand why I had such trouble. -As in the video I mentioned, you can do this installation without removing the front bumper/fascia by bolting the cooler it to the existing transmission oil cooler bracket, however, the flange on the Hayden cooler is not wide enough. You will need to fabricate some metal tabs to add width to the flange. -Also as in the video, I secured the right side using one of the provided plastic "zip tie" fasteners. -You have to remove the plastic skid plate/cover from just behind the bottom of the front bumper to access the transmission lines. I also had to jack the front of the car up and put it on jackstands to get some clearance to maneuver my arms. -There is a flat, roughly triangular metal bracket right below the transmission lines that is held in with three 17mm bolts. I removed the front two and loosened the back one and pivoted the bracket out of the way. Unless you have incredibly small hands and/or a lift, I don't see how you can do this job without moving that bracket but in the video he somehow does. There is also a small hose in the way that I disconnected 2 white clips from the car frame so I can move it around a bit. -I was concerned that there wouldn't be enough hose but there was about 9" more than you actually need for the MDX. Just be very sure where you cut so you don't come up short on one end. I used a pair of anvil pruning shears and they cut it beautifully. -On my 2011 (and in the video) the return line was the line that has a canister-style filter on it about 6" from the metal barb. Confirm though by running your engine, shifting through the gears, then shut the car off and feel the two hoses. The cooler hose is the one you will tie into. -Slipping off the hoses results in transmission fluid loss. I probably spilled about 1/8 quart doing this. If you have another person with you it might help but the area to work in is so tight I can't imagine it would help much. I slipped the new hose onto the newly exposed metal barb and then connected the old hose to the other length of new hose using the flared aluminum pipe Hayden provides and 2 hose clamps. Make sure you have the hose clamps on the hoses before you do the switch. You will need an extra hose clamp as well with this installation method. -When I turned on the car to check for leaks, everything was fine except I was getting a few very tiny bubbles at one of the connections on the flared aluminum pipe. I think the hoses on the Acura are about 1/16" wider than the 11/32" hose Hayden provides. I tightened the clamp down further and the bubbles disappeared. -Remember that you MUST replace not only the transmission fluid you spilled but also you must add a little bit more as there is now more capacity due to the new cooler and hoses. I added about 200 millilitres to start and will check after driving for 15 minutes and top up as necessary. Adding transmission fluid to the MDX is a minor hassle - you either need to have a funnel with a long flexible tube to fill via the dipstick or you need to open the fill port on the transmission which requires a long socket extension and some brute strength. I hope this helps someone!

I put this on my Chevy Astro 2003 as I found out it can help out a lot with the 4L60e’s. Everything went ok… I did have to stop by napa and buy extra transmission hose because of the way I put mine together. You almost certainly will need to buy extra hose. The most killer thing I did was actually connecting the hoses to my return line.. since gm decided to make a serviceable crimp style hose section on the trans lines. I had to take about 2 hours to figure that out and also how to make it look clean. Other than that everything else went smooth. I could’ve made brackets but I feel like that was a little too much for my price range. I also considered the spacers it came with and the zip ties which made everything easier to mount. You can see in the photo.

Installed on a 2008 Jeep JK Installed today on 8/10/25. Wasn't a bad job to do. Hardest part was bending the brackets and drilling the holes to mount it. So far after a hilly ride, I was sitting at 185⁰ which is fantastic. I did buy the hayden bracket kit for it and extra tubing. After install and driving I checked for leaks and such so far seems to be good. Time will tell for sure. So far it's worth the money for me. Cooling seems to be good, won't be able to tell for sure until I drive it more but so far can't complain.

Made it fit my 2003 Silverado z71 only problem you going to run into is this but no worries I gotchu. So what I did was split the oem connector on top of radiator in half bec the one that came with it was not the right size and buy a extra hose also bec it only comes with one you will need two and that’s prettt much it easy.