T-stat or no T-stat...that is the question.

[Decreasing_Dave]

I'm running the fan.  I even have a switch to turn it on while I'm waiting on the grid (this is the SW you know).

Do you guys and gals run a T-stat or just run an open flow??

Thanks,
D. Dave

[T595]

I am no mech. nor an experienced racer (am. only) but when i requested my mech. to remove t-stat he almost shot me... something to do with the overall running of electrical system and sensors etc... the fan starts in mid june in southwest/pacific and doesn't turn off till' late october...

[Eric Kelcher]

If you don't want the thermostat then gut it and reinstall just the housing or a large washer. You need a restriction to keep pump from cavitating at high RPM and also slow the water down so that it can absorb as much heat as possible and then shed that heat. if run full open then water does not rise to very high temp when it passes through engine so it is not very effiecent. The greater the temp differential of water to engine/radiator the more effective it is.

[TZ_Boy]

The thermostat has nothing to do with the electrical system of the bike.  The restriction that the thermostat gives is what in most cases helps the system to build pressure.  Pressure is what raises the boiling point of water significantly.  Most systems run 13 pounds of pressure.

[lightsmith]

The purpose of the thermostat is to constrict flow to aid in getting up to temperature.  Some systems are plumbed so that it actually diverts coolant through a bypass around the radiator.  If you have the bypass setup (not that common), don't mess with it.  Otherwise take it out.

Running a higher flow rate will help cooling as it brings as much hot coolant through the radiator as possible.  The metal to liquid heat transfer is much more efficient that the metal to air transfer rate.  The higher your flow, the more heat will be extracted from the metal.  

Pressure in the system is built due to the heated liquid being unable to expand because of the spring sealed radiator cap.  The cap is what limits the pressure.  If you have a 13 pound cap, that is the pressure that the system will run at.  Anything higher will be purged to the catch can.

Cavitation is not a result of the pump turning too fast, but rather the coolant boiling locally in the low pressure area of the "draw" side of the pump.  The high-school chemistry experiment shows how water can boil at room temperature if it is in a vacuum.  Coolant pumps typically drop the pressure on the "draw" side by about 5 psi.  

If you have cavitation problems, the solution is to raise the overall system pressure by changing to a higher pressure cap, or using a coolant with a higher boiling point.  

[Decreasing_Dave]

OK....Now I'm a little confused.  

Eric made a good point about the higher pressure and lower flow.  Lightsmith made a good point about the higher flow and the radiator cap controlling pressure.

Eric, when I read your post, it brought back memories of what I had learned in the past and had just forgot.  I felt good, kind of like an idiot, but good just the same.

Lightsmith, when I read your post, it reminded me of the very same reasons that I posted this question in the first place (i.e. faster flow, moves more heat).  I felt good again, but just as confused.

Maybe I should make this one of those "poll" post and we can all vote. ;D

Thank all of you for replying, but I still need help. ???

[TZ_Boy]

"When water pump speed increases to its peak efficiency speed it is not the radiator cap that stops boiling but water pressure created by the water pump.  Even many race engine tuners do not seem to understand that regardless of the radiator cap pressure a water pump spinning at maximum efficiency rpm will produce a pressure head of around 30-40psi in the engine when the water flow out of the head is limited by a thermostat or resrtictor.  This pressure packs coolant around the top of the cylinders and around the combustion chambers to carry away combustion heat and stop an insulating blanket of gas bubbles forming in these areas.  An old wives tale states that if you remove the thermostat the enginge can be damaged due to the water flowing to quickly to draw off heat, or it is flowing through the radiator to fast to give up it's heat.  This is not so, what causes the engine damage is a loss of pressure, so coolant isn't being packed in tight around hot spots in the engine."-A. Graham Bell
As far as having a switch to turn on your fan on the starting grid you have more important things to be thinking about than turning a switch on and off.  Removing your fan should drop your operating temperature slighty due to the fact that it is a 4" square blocking airflow through your radiator.

[lightsmith]

While it's true that a restriction on the exit of the cooling jacket will raise the pressure and boiling point inside the jacket, that won't stop localized boiling, hot spots, and detonation. It will slow the process, but under extreme conditions like high loads and hot air temperatures the problems will persist.     The real problem with the system is the pressence of water.  This is the reason that I'm happy to promote Evans NPG as one of our sponsors.  If you insist on running water, I suggest you leave the thermostat in (or at least the T-stat frame) and buy a bigger radiator.  I encourage you to visit the Evans website, www.evanscooling.com for lots of technical information as well as other interesting reading.  Check out the article about the demonstration they did at a construction site at 16,000 feet near Tibet!