Tunnel Heat Exchanger, Radiator Delete

Tunnel Cooler/ Heat Exchanger, Radiator Delete

So I know a few people have done this now, but I figured I'd give a quick description of how I did mine and how it has worked so far on my KX525 big bore 2-stroke. Feel free to post up how you went about it as well.

I used a front heat exchanger from an older Arctic Cat EXT 550. You can use whatever, that's just the one I found and it seems to fit very nicely in the Timbersled tunnel. I also used a radiator cap assembly from an '06 Arctic Cat Bearcat. Again, this just worked out because it was a 90 degree housing with a radiator cap, perfect for my needs. My cap is the highest point in the system, so it was fairly easy to bleed.

For a thermostat, I'm using the KTM 2 stroke thermostat and using the bypass to feed my carb heater. So, my circuit goes like this:

Head -> Radiator cap -> Thermostat -> Tunnel Cooler -> Water pump

I used smaller 5/8" hose to and from the cooler. The bike has 19mm or 3/4" hose everywhere, but I didn't want that much coolant in the system and 8' of 3/4" hose full of coolant weighs a lot. I think you save around .5lb running 5/8 hose instead of 3/4.

The bypass circuit is Thermostat -> Carb Heater -> Water pump (bypasses the cooler)

I first had the bypass routed Thermostat -> Carb heater -> Tunnel Cooler -> Water pump, but I couldn't keep the coolant temps up enough because there was too much cooling going on with the bypass circuit pushing coolant through the cooler.

For the first couple rides I ran a snow flap because I was concerned with not having enough cooling. It turns out that a tunnel cooler is extremely efficient and I haven't been running a flap for a while now.

At this point, I was still not able to keep the temperatures up in deep snow unless I was climbing for a while, so I made engine covers. Now I am running a fairly consistent 130ish degrees at all times. I also found that with covers, my coolant temp doesn't drop as rapidly when I stop to help dig someone out because the engine cases aren't packed with snow.

Going up a hardpack trail for a few miles with no ice scratchers, no snow flap, and staying out of the snow on the side of the trail, it climbs to about 165 degrees, but comes down quick as soon as you ride off the trail for a few feet. That's pretty good in my book. Ice scratchers would keep it more consistent, but I'll just get off the trail every once in a while like I should anyway.












I also found that header wrap on a 2 stroke snow bike pipe is not the best way to go. The wrap melts snow and sucks up water, giving the pipe a nice, cooling water jacket and makes it run like crap. I now have header wrap only in a couple places to avoid burning gloves or snow pants.

The other benefit of running no radiators is that you don't have anything there to rip off on trees.

I did the same exact thing on my yz300 and yz450f. all the info on my 300 one is on my yz300 thread, here are some pics from my 450f project, got rid of both rads on this one. I got my info from ravenous and egesledder and others on here so I would like to thank them for the ideas. I cut down a giant exchanger I had from a ski doo 800. It is 9 inches wide and I cut a 15 inch long piece of it using the end with the plumbing inlet and outlet. I had it welded back closed at a shop for 50 bucks. I had to mod the inside a little to allow the coolant to flow across the seperate chambers since I cut off the end where it originally crossed over. Its alot easier to start with a complete exchanger, the older arctic cat ones like egesledder mentioned are perfect, I used the one of those I had on my 2 stroke. I had a bunch of random hoses on hand from the donor sleds and then just bought about 10 feet of 3/4 inch heater hose from napa. I also used a few of the bikes original hoses here and there. I had a couple fill caps and fittings from the old arctic cat on hand as well. you must run a thermostat with this setup, I run the avid one, appropriate temp depending on 2 or 4 stroke application. most of the sled hoses were 1 inch so I had to size down and up here and there. I made some couplers and size adapters on my lathe from aluminum. you can buy plastic ones but I don't trust plastic too much, u could probably buy some brass stuff off the shelf (pex parts or just barbed stuff from a hardware store) if u don't have a lathe. I prefer aluminum. The hardest part is getting the air out of the system, I filled it from different points and let it leak here and there before tightening all clamps to get all air out, takes forever, makes a mess but once purged works killer, especially combined with scratchers on the skid for that icy trail. Temps are super consistent, no more wild swings! on cold pow days I run my engine enclosed, on warmer days without pow flying up I take the side panels off. I kept my radiator guards to suppport my bodywork in front, but I might ditch it all and go for the super naked look, not sure yet. I carry some pieces of hose and couplers with me at first, as well as some spare coolant, after u have done massive cooling system mods u better be prepared for a leak or other problem, if you are ready it wont happen! I also put little protective pads made from hose scraps on hoses anywhere they might rub, also watch out for the exhaust, this rearward exhaust yz was so easy to plumb and route hoses it was almost cheating!

Update, transferred my tunnel cooler setup over to my 2016 kit. I removed the rear plastic rod that supports the tank and the strap still has enough slack to hold the tank securely. I may make an extension bracket in the future if the tank moves around too much, but its really solid like it is now.

The rest of the setup is the same as it was last season, it all worked great. I mounted the cooler with 6 1/4-20 bolts.