Keeping Your (Engine) Cool

Home-Made Race Sled Cool-Down Cart

Nov. 01, 2005 By Steven LaMunion

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Figure 1 - Basic Cool Cart
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If you’re going to race your snowmobile during the warm weather seasons of grass or asphalt then you’re going to need a way to keep your engine temperature in control. 

Cool down carts, or “cool carts” are used to cool the engine coolant after a pass down the drag strip. These cool carts are usually home made. There are as many different designs as there are racers. While construction techniques vary widely the operating principle is the same: pump cool liquid through the engine to take out the heat. 

The most basic of systems can be made for under $100 worth of parts that are all available at your local home improvement store. The top end systems are limited only by your imagination and budget. I’ve seen systems as extravagant as 110 volt powered chillers that circulate coolant through a refrigeration system. I saw one unit that was so large it was servicing 4 snowmobiles at once. Cool cart construction is almost an art in itself. Walk around the pit area of any major race and you will find all kinds of ways to achieve the same end result. 

A basic system (Figure 1) consists of:

  • Cart to carry it all
  • Reservoir to hold your coolant (usually a cooler)
  • Pump (a 12v bilge pump works good) (Figure 2)
  • Hoses with quick connect fittings
  • Power source (motorcycle battery)

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Figure 2 - A simple 12V bilge pump sits inside
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The basic system shown in figures 1 and 2 is an “open” system. That means the coolant is dumped into a reservoir that is open to the atmosphere. A “closed” system would have a heat exchanger in the tank. The heat exchanger keeps the coolant from getting mixed with whatever is used in the tank. If you’re using ice to cool with and water/antifreeze as your coolant, you’ll want to use a closed system to keep the ice from diluting your antifreeze mix. 

 

This basic system relies on ice as the cooling media. With this system the sled is using straight water as a coolant. The water is pumped by the bilge pump, through the sled, and back into the reservoir. The ice is dumped directly into the reservoir. 

The pros to this system are:

  • It is the least expensive to build
  • Easy to Maintain
The cons are:
  • You need a much, much larger cooler to carry all your ice
  • If you run out of ice, you cannot cool down any more
I used a system just like this one for a couple of years. One particularly blistering hot day at the asphalt drags in the middle of July it came to me that there had to be a better way than hauling 100 pounds of ice around to the race track every weekend. I was spending more money on ice than I did to get into the race. 

That night, back in my air-conditioned garage, after a couple of icy brews and a pizza (Two necessary items for brainstorming. The brews help free your mind of preconceived constraints and the pizza box is where you write down your ideas) I wrote down a list of features that I thought a cool cart should have.

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Figure 3 - Combination Pit Cart/Cool Cart
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  • No ice required!!! (1st priority)
  • Inexpensive to build (2nd priority)
  • Self contained, holds all hoses, battery, pump, fluids etc
  • Easy to move, large tires to push through grass
  • A shelf for tools and a small work space to do clutch changes
What I ended up with was a pit cart that served two purposes. It served as my cool cart plus my pit cart with space on the top for a tool tray and an area to work on clutches (Figure 3). 

To break the dependence on ice, the cool cart had to provide cooling by other means. All the racecars at the track had the answer right under the hood. A radiator, pump, and fan. It’s not practical to install all that on your sled, and not really necessary either. For the amount of time the sled runs, from staging to returning to the pit, your water temp will be ok. The objective is not so much to keep the sled cool while running, but to cool it down to starting temperature for the next run.

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Figure 4 - Cross flow radiator and fan
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I scoured the local junkyards for a radiator and scored a “like new” cross flow radiator for $25 (Figure 4). The utility cart is right out of a industrial supply catalog for $59. Check around where you live for a surplus industrial equipment shop. Sometimes you can find these carts used. The twenty-gallon cooler I caught on sale at Walmart for $35. Inside the cooler are two 12-volt bilge pumps at $15 each. The fan came from Pep Boys for $50. The most expensive part of the whole setup is the Sears deep cycle marine battery. Some people use a motorcycle battery but I wanted the biggest, longest lasting battery I could get from Sears. I didn’t want to risk running out of juice. It would be just as bad as running out off ice.

 

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Figure 5 - Bilge pumps - visit your local boat shop
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I installed two bilge pumps but only one is working as part of the system. The second one is there as a spare (Figure 5). The biggest ¾” pumps available are rated at 800 gallons per minute. That is how much they pump when used as a bilge pump. In this installation they pump about 10 gallons a minute due to all the hose length, bends and other restrictions in your engine. You don’t need anything bigger than ¾”. If you put a huge pump in there it will force the water through your engine so fast that it will not pick up the heat from the engine.

 

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Figure 6 - Coolant return line feeds into the top of the radiator
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The pumping circuit starts at the bilge pump. It pushes water into the engine, around through the tunnel coolers and dumps back into the top of the radiator (Figure 6). The water gravity feeds into the radiator. When the radiator fills to the height of the tank return hose, the coolant spills out into the cooler. 

One thing I would do different if I were to build another cart would be to use something different for the coolant reservoir. The coolers are what 99% of people use but, to me, it doesn’t make sense that we are trying to cool down hot water while holding it in an insulated container. What would work really well here would be an aluminum container. Maybe an empty beer keg? The aluminum would dissipate the heat. There was only one event that I went to that the cart could not keep up with the heat and on that day I was cooling two sleds with it. Near the end of the day I finally dropped a bag ice into the cooler. One thing to note is that this system will only bring the coolant down to whatever the ambient temperature is. If it’s 95 degrees that day, then the coolest you will get everything is 95 degrees. Another tip - I found that when the system is not running on the sled, that if I just circulate the water through the radiator with the fan on, it will bring the temp down in the coolant to ambient. Last thing to remember, don’t leave the cart parked with the radiator directly in the sun. It heats up the water in the radiator. I usually throw a cover over the cart or park it in the shade.

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Figure 7 - Hoses coil up on bracket for easy storage
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The bilge pump and fan draw such little electricity that I’ve gone 3 race weekends without recharging it. I don’t recommend doing that, but it just happened that way and I was pleasantly surprised that the battery was up to the task. I’d skip the motorcycle battery and go right for the deep cycle workhorse. 

In my cart I run a 50/50 mix of water and antifreeze. I carry 8 gallons of it in two five gallons jugs. At each race I empty the coolant into the cart. When the races are over, I pump it back into the jugs and stow it in the trailer for the next race.

 

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Figure 8 - Switches mounted below the top tray on the cart
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On the end of the cart, fabricate up some brackets to coil your hoses on when not in use (Figure 7). Separate on/off switches for the pump and fan are mounted underneath the top of the cart (Figure 8). They are out of the way so they do not get turned on/off accidentally.

On a 95 degree day, with the sled at 180 degrees I can plug in the hoses, flip on the pump and fan. By the time I have the belt off the clutches, the spark plugs out and get the leaf blower started, the engine is cooled down. I usually let the water circulate for 5-10 minutes just to make sure all latent heat is pulled out of the pistons and crankshaft. Here is a tip for a good cool down. While the cool cart is running, as you are cooling the clutches with the leaf blower, rotate the crankshaft a ¼ turn or so every 10-20 seconds. This moves the pistons up/down in the cylinders and ensures that you don’t have one piston that stays hot because it was down in the crankcase while you cooled the engine. 

After you get a setup like this, you’ll wonder why you spent so much money hauling around ice before! 

Contact the author Steve LaMunion

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