DIY: Trans Cooler Install - Hayden 678 does fit...kinda.

Disclaimer: I take no responsibility for any damage you may do to your car following this DIY. Any work you do on your car, you do at your own risk.

 

When I bought my '05 Legacy 2.5GT Wagon recently as a more "family" oriented daily driver, I was forced to opt for an Auto Tranny because the wifey can't drive stick. After catching a bit of the mod bug for this car, I read of some of the problems 5EAT owners have had with the increased power levels of anything over Stage 2 and figured a trans cooler would be a good addition to help dissipate heat from the trans fluid (also looking at a HexMods F1 Modded Valve Body and maybe a trans rebuild eventually). Searched on here and found an install thread with a dead link, but a google search led me to this pdf: subaru.rockhopjohn.com/Transcool.pdf

 

It's a pretty good install how-to, but IMHO the cooler was plumbed incorrectly (more on that later). I just did a similar install and figured i'd post it up here since the link in the other thread is dead.

 

Most of the people that have added trans coolers have done so using the Hayden 1676 or the 676...the smaller of the 3 sizes that Hayden offers. I wanted to try to fit a bigger cooler (was looking for a 677) and the only thing my local auto store had in stock was the 678. People have stated that this cooler would be too big to fit the LGT, but a rudimentary measurement of the available space suggested it may fit afterall. Plus, it was the only thing they had in stock, and I wanted to do this install today (had a little bit of spare time today - very rare with 2 kids:D), so I bought it along with a little extra ATF. Here's the Hayden 678:

http://i277.photobucket.com/albums/kk56/atchipmunk/05%20LGT%20Wagon/TransCooler-1.jpg

 

And here's what the cooler itself looks like:

http://i277.photobucket.com/albums/kk56/atchipmunk/05%20LGT%20Wagon/TransCooler-4.jpg

 

Included in the kit is the cooler core itself, 4ft of hose, 4 screw-type hose clamps, and the mounting clamps for the cooler. The other thing you'll need to buy is a 3/8" barbed hose union, like this (you only need one):

http://i277.photobucket.com/albums/kk56/atchipmunk/05%20LGT%20Wagon/TransCooler-2.jpg

 

So, I started by opening up the hood and removing the front grill to access the area where the cooler will mount. I chose to mount it in front of the driver's side of the condenser. Here's the space i'm looking to mount it:

http://i277.photobucket.com/albums/kk56/atchipmunk/05%20LGT%20Wagon/TransCooler-3.jpg

 

I ran the hoses to the core, secured them with hose clamps, and fed the cooler into place. I'm not really a fan of the clip mounts they provided for mounting the cooler to the condenser/radiator, but there aren't really any available empty threaded holes in the surrounding area that I could fabricate brackets to, so I just used the supplied mounts for now. Follow the manufacturer's instructions for proper usage of these mounts. Here's the cooler mounted in place:

http://i277.photobucket.com/albums/kk56/atchipmunk/05%20LGT%20Wagon/TransCooler-5.jpg

 

Yes, it BARELY fit in there. Honestly, it's actually a TAD bit to big. The core itself is perfect, but the hose connections actually slightly contact the hoses/mounts on the condenser. To help prevent it from wearing holes into the hoses, I put some isolating pieces in between the hose and the condenser mounts. I'll keep an eye on them to make sure they don't cause any issues, but it should be ok. In hindsight, it probably would been better to go with the Hayden 677 or the more commonly used 676, but oh well...on to the plumbing!

 

The LGT with the 5EAT already has an liquid to liquid trans cooler built into the bottom of the radiator using engine coolant to pull heat from the trans fluid. When adding an auxiliary liquid to air cooler to this circuit, you want to plumb it in in series after the stock cooler, before the fluid returns back to the transmission. This gives the most additional cooling capacity. The line that needs to be tapped into sits on the driver's side front corner below the framerail and battery. I was able to access it and do all the work from the top side of the car and didn't put the car up in the air at all. In order to access it, you must first remove the coolant overflow tank. To remove it, pull the hose from the top of the tank and press the retaining tab to release the corner of the tank. It then just pulls out of place. Here's a pic:

http://i277.photobucket.com/albums/kk56/atchipmunk/05%20LGT%20Wagon/TransCooler-6.jpg

 

Once the coolant tank is out of the way, you can see the trans cooler lines towards the bottom of the car. They can be seen here (2 hardlines coming down off the framerail connecting to 2 rubber hoses):

http://i277.photobucket.com/albums/kk56/atchipmunk/05%20LGT%20Wagon/TransCooler-7.jpg

 

The rearmost hose (top one in the pic) is the return line back to the transmission from the stock cooler. That is the one we want to tap into. It is held on by a squeeze clamp. Squeeze the clamp with a pair of pliers to release it and slide it downward and remove the hose. At this point, I plugged the stock hose with an appropriately sized bolt, and capped off the hard line with one of the plastic caps that came on the hose connections on the cooler core. This helped to minimize fluid loss while I was trimming the auxiliary cooler lines to the proper length.

 

About those lines. I mentioned earlier that I thought the cooler in the other .pdf was plumbed incorrectly. I say this because it was plumbed so that the fluid flows from top to bottom of the cooler before it heads back to the transmission. While there is much debate to which direction the fluid should flow through an auxiliary cooler, IMHO the proper flow is from the bottom up. The reason is to ensure it bleeds air properly as any air bubbles in the cooler core will reduce it's cooling effectiveness. Flowing from bottom to top practically ensures that the cooler will be bleed as it's much easier for the fluid to push air upwards (the direction it naturally wants to travel) versus pushing it downward through the core. That being said, we want to connect the upper hose off of the trans cooler (the outlet hose) to the hardline side of the return line. On the lower cooler hose you want to install one of those 3/8" Barbed Unions using hose clamps (don't tighten them too much) and connect it to the rubber side of the return line coming from the stock cooler. Here's what mine looked like after I connected the lines:

http://i277.photobucket.com/albums/kk56/atchipmunk/05%20LGT%20Wagon/TransCooler-9.jpg

 

And another one from a different view:

http://i277.photobucket.com/albums/kk56/atchipmunk/05%20LGT%20Wagon/TransCooler-10.jpg

 

Now, all that's left to do is to make sure the hoses don't contact any sharp edges (using zip ties to hold stuff into place if necessary), top off the transmission fluid (make sure it's at operating temp when you check the fluid level), re-install the coolant overflow hose, and enjoy the added cooling for your trans fluid. You'll definitely want to double check all your hose connections after starting and running the car to make sure they don't leak.

Total work time for me was about an hour, including clean up time of the fluid that did spill from the hoses. If I had even more time to work on it, I woulda chose to pull the radiator so I could mount the cooler to just the condenser using the supplied clips and not through both the condenser AND radiator. Maybe if I ever upgrade my radiator with an all aluminum one, i'll do just that. Anyway, I hope this helps anyone looking to add a cooler to their car...

 

Alvin Caragay

Hermosa Beach, CA

'05 BSM LGT Wagon (Cobb OTS Stage 1 tune)

Edited November 23, 2011 by atchipmunk

Someone feel free to factcheck me if I'm wrong. But I was always taught to plumb the auxiliary cooler in before the one in the radiator. This helps is done to help regulate the transmission fluid temperatures as ambient temps can have a wild effect on fluid temp throughout the seasons. Since the coolant in the radiator is basically a thermal mass that is a more consistent temperature as compared to ambient temps is can help prevent overcooling or continue to help any further reduction. The basic premise however being not only cooling of fluid temps but regulation as well.

 

Dan

Wow great write up. I might end up doing this as we hit the mountains a lot in the summer months with 100+ days.

Someone feel free to factcheck me if I'm wrong. But I was always taught to plumb the auxiliary cooler in before the one in the radiator. This helps is done to help regulate the transmission fluid temperatures as ambient temps can have a wild effect on fluid temp throughout the seasons. Since the coolant in the radiator is basically a thermal mass that is a more consistent temperature as compared to ambient temps is can help prevent overcooling or continue to help any further reduction. The basic premise however being not only cooling of fluid temps but regulation as well.

 

Yeah, there are definitely 2 schools of thought on this. The transmission fluid can be too cool, and if I lived in an area that saw all 4 seasons and had to worry about the fluid being cooled too much during the winter months I would probably opt to plumb the aux cooler in before the stock cooler so that the stock cooler could help regulate the temp. Here in sunny SoCal that shouldn't really a problem, hence the choice to plumb it after the stock cooler...

Thanks for the DIY.

I just installed a 678 this past weekend along with a Mishimoto radiator. I mounted mine slightly higher to avoid the hoses contacting the condenser inlet and outlet. The lower fitting on mine is just above the lower condenser fitting. I ended up having to trim a corner off of the condenser mounting bracket, but other than that, it's a clean install that just barely fits. Anything bigger would definitely be a no go. Trans temps so far have never gone past 195, but typically hover around 175 to 180.

How are you guys measuring ATF temps? I've got a Scangauge, and there's no temperature sensor connected to the tranny. Or is it just the same as the coolant/water temp, since the tranny is cooled by that?

is anyone using a thermostat to control fluid flow to the separate cooler?

faster warm ups, with no fear of over cooling sounds like a good plan to me..

I'm using a Tactrix 2.0 for logging the transmission temps. It's definitely not the same as the engine coolant temps, especially on my setup, since I'm running a Mishimoto radiator which doesn't have the built in trans cooler.

 

As far as a thermostat, I didn't install one. I'll probably do what I've done in the past on other cars and install a baffle during the winter to reduce cooling.

Thank you.

 

Pulled back fender liner to get better access and plumped in pre-rad for freezing temps we get here.

Went out and did some trans temp logging on a 100* day today. Started out with some driving, then 10 minutes of idling to cool down to a base temperature of 176/176. Several hard pulls later peaked out the system at 203/221. Temps remained 203/212 for 20 minutes of freeway cruising, creeping up to 203/216 with some accel at freeway speeds as well as on surface roads. Three minutes of idling and the temps came to 199/203 and dropping.

 

So the Hayden 678 works well enough to be used as the only ATF cooler. With those temps, it seems a good change interval would be about 30,000 miles.

that is great data koukis14,,,,

 

so 100 deg F at 5,000+ft elevation eh? yeah, that will strain all fluids and fluid systems.

Great DIY instructions! Thought I would throw in my experiences installing a Hayden 677 in my 2013 Legacy Limited. This is the 2.5 engine with the CVT. I made the assumption that the fluid lines flowed the same as the regular automatic. WRONG. The hoses are BACKWARD in the CVT. The REAR hose is the HOT fluid from the CVT. I verified this by installing a short piece of clear hose, starting the engine and watching the fluid direction flow. My install goes from the hot CVT through the Hayden cooler, out the top of the cooler and through a Magnefine filter. Then it goes through the radiator cooler and back to the CVT.

Update: After 30 minutes of highway driving on a 90 degree day, the temp of fluid coming from the CVT and going into the cooler is about 152 degrees. Coming out of the cooler 127. What I find interesting is that now the fluid goes into the bottom of the radiator cooler where the coolant measured about 145 degrees, so the radiator cooler is actually going to WARM the CVT fluid. This might be a good thing to keep the fluid at a more constant temperature, especially in the winter.

This is a good thing, since you have a more controlled temperature.

 

The tranny is connected to the rad to bring it UP to temp faster.

Does anyone have thoughts, or better yet actual measurements of the increase in pressure caused by placing a transmission cooler and/or fluid filter (like the Magnefine) into the cooling loop? I'm sure there is some added restriction that increases fluid pressure... just wondering how much and is that a negative affect? For instance, does it put more stress on the fluid pump mechanism in the transmission?

Considering that the trans pump is capable of generating several hundred psi, I'm sure any restrictions in the cooling loop are inconsequential. I seem to remember reading that typical cooling loop pressures are around 20 psi, give or take 10 psi, depending on the vehicle.

So the CVT doesnt have an OEM filter somewhere? Interesting.

 

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I have looked around on the outside of the CVT and not found anything resembling a filter. I'm sure it at least would have one internally, but I have no idea the quality of filtration on it. Don't have access to a FSM. Next time I head in for an oil change, will ask about built in fluid filter. If it has a good quality one, I might consider removing the Magnefine. I read a lot of good things about the Magnefine, and I especially like the fact I can easily change it out. It is strapped to the frame right near the radiator overflow bottle. I figured changing it every 25-30k miles would be good. I only have 8K miles on my Legacy and have a 2" receiver to do some occasional trailer towing. Probably get the CVT drained and filled when it's time to change the filter. While I don't do heavy towing, I don't buy the CVT fluid being "lifetime" under normal driving conditions.

 

QUOTE=jp233;4573466]So the CVT doesnt have an OEM filter somewhere? Interesting.

 

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Edited September 19, 2013 by mjb32803

Question regarding the size of the inside diameter of the cooler line hose!

 

The Hayden cooler comes with cooler hose that seems too small to fit/too tight on the Subaru's cooler line and radiator fittings. This is for my 2009 Outback LTD 2.5i by the way, but the cooler line size I believe should still be the same i.d. as the GT. Then went to the auto parts store with a sample piece (same size that fit my Lexus from that easy install), and they couldn't figure it out; I think they were just out of the right size and didn't know what they were doing, and it was late. My car is down now, because I thought I had all the parts but learned the hard way.

 

Is it just standard off-the-shelf 3/8" i.d.?

 

Thanks!

Just bought the cooler for my 5eat. How is everyone experience with it and with the walkthrough? My car is a spring and summer car but I do live in a 4 season area so the temps in early spring or late summer def go down to 40s

 

 

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I have my Hayden in for 60K miles. No issues. Just don't remember which model it was. It does have the thermostatic bypass.

Just bought the cooler for my 5eat. How is everyone experience with it and with the walkthrough? My car is a spring and summer car but I do live in a 4 season area so the temps in early spring or late summer def go down to 40s

 

 

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My experience was great with the Hayden cooler and a thermostat and computer fan on it, living in a warm and cool climate in So Cal, pulling hard in mountains and deserts four seasons. It also gave me a good way to purge fluid to all new. It kept the trans (and and as a secondary effect, engine coolant) cooler in hot weather but the engine thermostat prevents over-cooling.

 

Unfortunately, my beloved '09 2.5i Limited was hit on the driver's side front totaling it, end of that story. Fortunately, I installed the cooler and fan in a well protected area (all else in that area was really smashed) and I removed it at the body shop when they told me I wasn't going to get anything for any of my extras and care. It took about 15 minutes to remove and connect the hoses back to the distorted radiator and clean up my drips. I intended to find another '09 2.5i Limited and tried for many weeks, but no luck in So Cal in the limited time I had. I had to replace the car with a more modern Mazda CX-5 to get a car with a trans that shifts, but can't add a cooler to modern cars like CX-5's because the minuscule built-in coolers have engine coolant routed internally without external trans fluid circulation.

 

I think this is what is relevant to your question: The CX-5's light-duty internal cooler has the trans running at about 190 degrees+ (normal trans operating temp, give or take a few degrees from a dash mounted OBD gauge) and uses a special very expensive fluid, compared to about 160 degrees or less with the Hayden cooler on the Outback or my Lexus RX300 as measured by the Hayden adjustable fan thermostat setting that only needs to cycle momentarily when the engine coolant stops circulating when I stop the engine (heat soak) or in extremely hot weather in traffic.

Edited December 7, 2019 by 2000GTWagon
Grammar

Nice. I got the Hayden 676. Apparently a good size for the LGT. Doesn’t have any sort of fan or thermostat but should do the job. I have my trans drained so I figured what better time than now to disconnect some hoses. Should be here tomorrow and I can install that and button up my valve body install.

 

 

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All finished. Came out good. Only took an hour. Totally worth 38 bucks to do this.

 

 

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