The Honda ST1300 and ST1100 are my favorite Sport Touring motorcycles. I have owned both, and they are very different machines. The ST1300 brought many improvements, but one very big problem. Riding the ST1300 throws off large volumes of hot air from around the engine. After an hour or more, the frame and fuel tank can be very hot to touch. That can be very uncomfortable for the rider's lower legs. The heat off the back of the fuel tank is severe. My private parts are so hot, it reminds me of the holiday song about "roasting over an open fire".
There have been many discussions of the cause and possible cures for this condition. Some believe the catalytic converters cause the heat, which can be rectified by changing to mufflers without cats. Been there, done that. No effect on the heat. That should not be surprising as the cats are contained within the mufflers out back, but the theory is the hot pipe carries the heat forward. I like my new mufflers, but if your goal is reduction of heat - save your money, it won't help.
The biggest source of heat in a water cooled motorcycle is very simple - its the radiator! In a well designed water cooled motorcycle, heat off the radiator is directed downward under the motorcycle, or well out to the sides. Unfortunately Honda did a really poor job designing the ST1300 cowl and frame with respect to heat dissipation. Not only does the design not direct heat around the rider, it actually traps the heat inside the cowling. This is really surprising, as most other parts of the bike show great thought. With the ST1300 cowling and air cleaner box removed, we can see two problems to correct . The pictures below show how I solved this problem for less than $30 in materials.
PROBLEM #1: THE ALLOY FRAME TRANSFERS HEAT DIRECTLY TO THE RIDER'S SHINS. The alloy frame begins just behind and above the radiator. That's not unusual, but there is nothing to deflect the air out or down, to reduce the heat transfer to the frame. Given time, the frame can get very hot. Notice the ST1300 picture above, the bright silver section just above the center stand? That's the exposed frame! As the frame is heated by the radiator in the front, the entire frame gets hot. If you like to ride on cool winter days, this is great, but most of the time that's a problem. The previous model ST1100 has tubular steel frame which is entirely covered by plastic. The ST1100 rider is not directly exposed to the hot frame. I don't know of a practical way to cover ST1300 exposed frame section, but if we can deflect the air down and away from the frame it won't get hot in he first place.
PROBLEM #2: THE COWL AND FRAME DESIGN ACTUALLY TRAPS THE HEAT. There are large openings between the frame and engine, directly behind the radiator as shown above. Hot air comes into those openings, and is trapped between the engine and the fuel tank. This heats not only the frame, but also the fuel tank that sits above. The only air exit from that space is at the back of the fuel tank, which exits directly into the rider's crotch! If we can block the air coming into this space, the problem could be largely eliminated.
Reflectix is a metal foil insulative wrap, sold at sold at Lowes, Home Depot, and other building suppliers. Reflectix does not tear or burn easily, but can be cut with a razor blade or scissors. It comes in many sizes. You want the 25ft x 24", for about $25. That is enough to complete several ST1300 in this process. There is a smaller roll, but that is 16" wide, which is not enough for some of the pieces.
You will also need foil tape. There are many varieties available, including one with the Reflectix brand, but any will work. At under $5 for the tape, our total investment for this project is about $30.
Step #1 is to remove the ST1300 side fairings and the air cleaner housing. Take it down to where you can see the throttle bodies in the pictures below. If you have never synced the throttle bodies (starter valves), this is a good time because they are now exposed. You'll see the big opening in the picture above.
The objective is to seal the gap all the way around the engine to the frame. Your first piece above goes at the right front corner where the biggest hole is. Trim openings for the cables and hoses as necessary. Don't worry about being fussy because gaps will be hidden by the foil tape. The Reflectix is cheap, so if you cut a piece wrong, you'll have plenty to use.
This is the first piece as shown above. Notice the idle adjustment cable coming through the insulation, you will reference that in the pictures below.
Again on the right front corner gap, now add another piece on the outside. More layers equals less heat transfer. Notice the idle adjuster at the top of the image, for location reference.
Now move to the left front corner. This opening is huge! Your ST1300 probably won't have the chain balls, those are part of the Audiovox cruise control I added.
Left inside the frame, continue all the way around both sides toward the back. Notice how the foil goes underneath the vacuum hoses at the back of the engine. The objective is to create a sealed area so the heat does not come up to the fuel tank or the motorcycle frame. Run the foil underneath the frame crossbar. We are going to continue the heat barrier all the way under the rider seat without a gap. Foil tape is your friend.
The fuel tank is metal, and touches the frame at the back. In order to reduce heat transfer to the tank, make pads at both sides. These cannot be thick or the tank will not sit properly over the frame. I tried insulating the entire way up the tank, but there is not enough clearance. Engine compartment and gas tank pads all done.
Remove the bracket which holds the back of the fuel tank to the frame. That will allow you to run the foil completely through and under the rider's seat. We are ducting the hot air down and below, so don't let it come back up to your private parts. Use as many pieces as necessary, just tape them together. With rear tank bracket removed, this area is exposed. Continue the foil all the way back on top of the lower fuel tank. Be sure to leave those bolt holes exposed, or you won't be able to reinstall the bracket.
This is the right side, where the cowl will later be reinstalled. The cowl is also designed to trap hot air within itself. Attach a large piece at the top, then reposition the cowl without all the fasteners. Use the cowl to mark the edges so you can trim the foil away from the openings. This will insulate the cowl and direct the air to the desired openings. There is not much clearance inside the cowl, so you may have to trim away some foil areas during reassembly.
Now on the left, outside the frame. Damn that radiator is close! Foil shown is on the outside of the big hole, protecting the frame against heat transfer, and deflecting the air downward. Now make a bigger piece on the outside left front. This one deflects more air downward, and gives us another layer against heat transfer to the frame.
On the left are the original Honda panels that fill between the radiator and the cowls. Many ST1300 owners remove these panels to increase flow of cool air to mix with the hot radiator air. Some others drill holes in the panels. Both methods help, but I did not want to leave the panels off for appearance, and I don't think the holes allow enough airflow. On the right are my modified radiator to cowl panels, with considerable area removed. Looks as if they were made that way, and lots more air.
Upon testing, I continued the foil panels down the side below the rider, along the battery and shock absorber adjusters. Be careful around the battery, as the foil panels will conduct electricity. I also added foil inside the back of the cowl, in front of the rider's knee. I neglected to take pictures of those areas, but will add them the next time my cowl panels are off for other service.
DOES IT WORK?
YES. This method absolutely does work. Heat spilling onto the rider is now negligible, no more than my other motorcycles. More important, my private parts are no longer being roasted over an open fire. The whole job will take 2 to 4 hours, depending on your experience in removing/installing the ST1300 bodywork. Good luck!