Indy Project Sled - Late-Model XC Coolers

Nov. 01, 2005 By ORC STAFF
Cost: $150 (US)
Risks: Requires modifying the tunnel, could cause serious problems if you misdrill
Benefits: Small weight saving, better cooling
Tools Required: Typical mechanic's toolkit, hole saws, ingenuity
Parts Required: Tunnel coolers, front cooler (optional)
Mechanical Skill Required: Slightly above-average "shade tree" skills

Here's another mod that I did because of other things I had done to the sled. The germ of the idea sprang from the chaincase roll, which sprang from the hope of weight saving. The reason I rolled the chaincase on a midwest trail sled was so that I could install a "super-cooler" front cooler and remove the side coolers. It turned out that for a trail sled, the single front cooler was not enough. I found that out after I had rolled the chaincase. Then when I tried to reinstall the stock running board coolers, I found that I had created some nasty clearance problems and had to hack up the right footwell to make it all fit.

Any rational person would have left well-enough alone, but then, what rational person would modify a snowmobile? Now that I think about, what rational person would *ride* a snowmobile? *grin*

So, when I first laid eyes on a new '99 XC, the first thing I noticed was the running board coolers were gone, replaced by small "tunnel protector" style coolers in the tunnel. The rusty gears began to turn and I realized what I had to do: install the '99 tunnel coolers on my project sled.

I was fortunate enough to find a set that had been removed from a sled that was being race-prepped and picked them up for a reasonable price, along with a used RMK front cooler. Now, you can only use the RMK font cooler if you've rolled your chaincase, but if you have an 80's or early 90's Indy, your front cooler is miniscule, replacing it with a large, later-model cooler is an option even if the massive RMK front cooler is not. And cost-wise, even if you have to pay retail for the parts from Polaris, they are not going to break the bank.

However, before you go grab your hole-cutting bits, there's more to the story, as usual with mods. I was also in the midst of replacing the stock Fuji 500cc twin with a Rotax. And at that stage of the project I was pretty sure I'd be running air socks and no airbox, the fact that the coolers' front connectors protruded into the engine compartment right under the airbox did not seem to present a problem to me. If you are running a stock Polaris motor and a stock airbox, it will be a problem for you. This is not a mod for an otherwise stock Indy, in other words.

But if you think it would cool to do (which, after all, is the main reason we do *any* mod, is it not?), it's not that tough, about a good afternoon's worth of work. It'll require some ingenutiy on your part to replumb the coolers. For me, the Rotax and the Polaris coolers mated up like they were made for each other. If you're going to put a Rotax in your Indy, this is a real neat trick to make it look like a professional job. But more on that later.

Start by yarding off just about everything anywhere close to the tunnel, including the seat, the gas tank, the oil and coolant bottles, the airbox, etc. The suspension has to come out also. Then drain the cooling system and start yanking out the hoses.

If you're going to replace the front cooler, it's a much more involved job and if you really want room to work the driveshaft has to come out. If you're putting in an RMK cooler, the outlet/inlet are both on the right side, so getting at them is a little easier with the motor in place. If you are going to install a newer/later-model cooler with the inlet and outlet on opposite ends, you'll have to figure out a way to get the hose clamp tightened on the end under the motor. The RMK cooler required covering up the steering post bolts, so if your steering post is in marginal condition, change it first. It also required cutting a new hole on the right ride of the bulkhead for the upper outlet. This hole is inconveniently located right at one of the bulkhead crossmembers on my '90 chassis. I left as much of it in place as I could, while still leaving room for the hose and clamp.

Putting the tunnel coolers in is much easier, in comparison. I used the rear cross-over coolant hose from Polaris as a locator guide when determining where to cut the holes. You'll need to cut two holes in the rear of the tunnel and two in the front. The two in the rear will stick up into the rear storage compartment - you'll have to cut a hole in the seat bottom.

After you have located and drilled the holes for the inlet/outlets, pop rivet the coolers in place.

Plumbing up the coolers will depend on what motor and front cooler you have in your sled. As I said above, with the RMK front cooler and the Rotax, everything except one hose hooked up like stock. Whatever your configuration, you'll have to improvise a little.

Once again, as with a lot these modifications, the benefits are not overwhelming. If you're doing a chaincase roll or an engine modification that will require more cooling, this might be a good mod for you. For a stock Indy 500, it's a lot of work and expense for little return. And it does have a downside: it takes away the built-in foot warming action of the running board coolers.

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