DIY Coolant Overflow / Reservoir Tank

 How it Works

When a liquid is under pressure the boiling point rises. When things are heated they expand. The coolant system is a sealed system, and when the coolant system heats up, this automatically generates pressure, because of this expansion. This is good, to a point. The hotter it gets, the more pressure it builds, and the higher the boiling point of our coolant. We cant let the system get to hot (Not much over 235F) or build to much pressure because, the rubber hoses that the coolant runs through might fail or we might just end up overheating altogether and causing more extreme damage (most likely).

So what happens when the coolant system builds to much pressure?

The cap has a built in pressure valve that lets off the excess pressure. This excess pressure or excess coolant that has now expanded and needs to leave the coolant system needs some place to go other than the ground. This is where the Coolant tank or Coolant expansion reservoir tank comes in. The coolant is captured in this tank.

What happens when the Coolant system cools down?

When the coolant system cools down, the system creates a low pressure area (lower than atmospheric pressure). This void or vacuum in the coolant system draws the coolant back out of the tank and back into the system. (You physicist will say the atmosphere pushes the coolant back into the coolant system.)

Now you see why we just don’t dump the coolant out on the ground. We need it later when the system cools back down, so we have a sufficient amount of coolant when we go back out.

Now that we know how it works, LETS BUILD A LIGHT WEIGHT VERSION.

Materials list

• 2 1/4″ 304 Stainless Steel Vibration-Damping Loop Clamps with Silicon Cushion or maybe I should use Zip Ties (Probably most common method)
• Durable Nylon Tight-Seal Barbed Tube Fitting, 90 Degree Elbow, 1/4″ Tube ID x 1/8 Male Pipe Size This is a 10 pack so I only need one pack. $7.50
• 8oz Wide Mouth Plastic Shipping Bottle $6
• Loctite General 2 part Adhesive I use this 2 part adhesive around the house and shop so I can justify the price tag.
• High-Temperature Silicone Rubber Tubing 3/16″ID-3/8″OD With your choice of color 10ft is more than enough and will do anywhere from 2 or 3 bikes. There is no shame in using the old tubing that came with the bike, so this $13 item is optional.

Below is the most common way to build your own coolant reservoir.  There is nothing wrong with doing it this way, but I myself have a problem with it.  When the coolant system does boil over and the reservoir is filled or maxed out.  Where does the coolant go?  The coolant will go all over the place and possibly onto the racing surface This will cause issues for you and the guys behind you.  Not only is there the possibility of leaking onto the track, and shutting it down for a bit. Allowing the coolant to blow past the hose and go where it wants will also make a mess of your bike causing coolant to go everywhere. I feel there is a better way to control coolant overflow.

This is the most common way to make a coolant reservoir. A hole is drilled in the cap and pushed into the container until it reaches bottom.  This will then draw coolant from the reservoir and back into the radiator.

8oz bottle and 3 90 deg fittings

Drilled pilot holed in the cap

Enlarge the holes just large enough for the threads of the fitting to pass through the holes. I did not spend the extra time tapping the holes for the fittings.

This is basically how it should look. The coolant in and the coolant boil-over out.

Trimmed up one of the barb fittings like so. Leave some material, because some of the length will be lost when inserted into the male pipe thread end of the barb / pipe fitting. Trim up some of the fitting so that the cut end can slide into the other 90 deg fitting, like below.

The sanded down barb fitting will fit into the male pipe thread end of the Barb / Male pipe threaded end of the fitting. Before putting these items together with epoxy. Sanding the surfaces that will be epoxied will ensure a good mechanical bond. I recommend cleaning them thoroughly with rubbing alcohol. This will ensure all the excess release agent will be cleaned off and the epoxy will have a clean surface to adhere to.

I used a two part epoxy by 3M to fuse the two parts together. I found using this was the best method to seal up the nipples.

Mix the epoxy until the color is uniform. I only have 10 minutes to work with this stuff before it starts to set up. It takes 24 hours for full cure, and 3 days for maximum cure.

I twisted the trimmed fitting into the pipe side. Twisting helps get the epoxy into the joint for a solid seal and bond.

The epoxy works its way under around and through the hole. A bit more needs to be added on the underside to prevent the fitting from pulling out.

This is the finished unit. I placed epoxy onto the pipe threads of the fitting and inserted it into the slightly over-sized hole. I am trying to get the epoxy to seal the area around the fitting

Attaching a short length of hose to the flair fitting on the inside of the bottle. As long as the end of the hose in the bottle is submerged in coolant, it will draw coolant from the bottom of the bottle, and flow back into the radiator when the coolant system cools down.