This is a schematic of a fuel injected thermostat bypass system. Coolant flows from the head of the engine to the
thermostat body. If the coolant's temperature is less than the opening temp of the thermostat, it will bypass and
go thru the insulated line to the water pump to be recirculated. Eventually, the coolant will reach the targeted
temperature and the thermostat will open. In the meantime, the engine will be warmed uniformly.
This is a schematic of a carbureted system. It is basically the same as the fuel injected system except the
bypassed water goes thru an insulated hose and on to the heat collar attached to the bell of the carb. This will
heat the carb to a temperature above freezing and will prevent ice from forming. This system works especially well
when used with our included neoprene carb jacket.
Our heat collars are clamp on style. This makes them easier to take on and off. You only have to loosen two set screws.
We have designed a clamp on style water jacket that fits on to the intake bell of the several carbs. The heat from the engine will warm the intake of the carb and help prevent ice. We have heater units for the Lectron, billet Smart carb, cast Smart carb, Keihin PWK and the Keihin FCR carb.
The picture on the left shows a standard carb heater kit. We have selected the finest quality components for this
kit that we could find. The bypass hose is made to be flexible in very cold temperatures. We supply an insulating
jacket for bypass hose.
The hose clamps are European style. They won't dig into the hose when you tighten them down. The "Home Depot" style will dig into the outer surface of the hose and damage the cover.
The thermostat body is six-sided. You can rotate the inlet and outlet to fit your particular situation. We include a neoprene carb jacket that will insulate your carb and heater from the outside environment.
The body is also threaded, so you can install a temperature gauge. You will know the temperature of your coolant
right out of the head at all times.
Our thermostats are specially made with stainless steel bodies. They will hold up under extreme vibration. We have a choice of 130 and 190-degree thermostats.
Below is a picture of our carb boot installed.
- One system for the carb models with the carb heat bypass.
- The other for the fuel injected systems bypassing the coolant directly to the water pump.
"Most internal combustion engines are incredibly inefficient at turning fuel burned into usable energy. The efficiency by which they do so is measured in terms of "thermal efficiency" and most gasoline combustion engines average around 20 percent thermal efficiency."
Motorcycle manufacturers know this. They also plan on their machines being run at 60 degrees and above
temperatures. There are several ways for these machines to get rid of heat. Heat can radiate out of the engine
case and exhaust pipe. If you have ever burned your leg on the pipe, you have experienced this radiated heat. Most
modern engines are water cooled. Water is heated in a water jacket around the cylinder and this water is pumped to
the radiators where the heat is removed to the ambient air.
Cooling systems are designed so that the engine will run at a designated temperature. The size of the radiator
etc. is adjusted so that the engine will run at these temperatures. Again the outside air temperature is taken
into account. In most cases, no thermostat is needed.
Most motorcycle thermostats are remotely mounted. That is, there is a length of hose from the cylinder head to the stat. Not a big problem in summer operating temps, but could be in the winter.
Depending on the length of hose, a lot of coolant temperature can be lost thru the side of the connecting hoses. You could end up with the coolant in the engine being too hot and the stat not opening because of this heat loss.
A bypass system solves this problem. The bypass line is plumbed before the thermostat and reconnects just before
the water pump. The water pump can flush the coolant thru the engine's head to the thermostat body quickly. If the
coolant temp is below the thermostat setting, the stat stays closed and the water returns to the water pump via
the insulated bypass line. The engine only has to warm up the coolant inside the engine and the small amount that
is in the bypass line.
Once the water reaches the stat's setting, the stat will open and the radiators will start operating. If for any reason the engine's temps drop below the stats setting, it will close and the whole operation will start over again. If you have a temp gauge, you should see the temps vary a little. If you have a 135 degree stat, you should see somewhere between 130 and 135. The temps will cycle back and forth as the thermostat opens and closes.
Manufacturers base their engine tolerances on an assumed operating temperature. Metals expand when heated. If you
run these engines cooler than designed, the piston/cylinder tolerances will be less than designed. In 4-strokes
the same can be said for valves and valve guides. EFI systems are also based on this same temperature. If it isn't
reached, the EFI will stay in "choke" mode and you'll end up over fueling your motor.
There are a couple of scenarios where this system isn't enough to control the engine heat. I get calls, usually
in December and January. The customer's bike isn't getting up to temperature. They think that the thermostat is
stuck open. Now anything mechanical can fail, but 99.9% of the time the customer has been riding thru handlebar
deep snow. In these conditions, the snow rubbing on the engine case and pipe is acting like a radiator.
It is robbing the engine of its heat before it can heat the coolant. This is where an engine cover comes in. In
deep snow conditions, you need one of these to get your cooling system to operate as designed.
From time to time I'll get calls about an overheating problem. These people are usually running the 500cc two strokes. On dirt, you can't run these bikes very hard as you can get going pretty fast very quickly. Not so with snowbikes. With track spin, etc. you can run the engine very hard and create enough heat, the stock system can't get rid of it quickly enough. Bigger radiators and/or other cooling systems are needed in these cases.