Join Date: Oct 2005
Location: Pensacola, Florida
Re: Engine Temperature
You make a good point, Woody. We need all the cooling we can get in summer, but have too much in winter. Rock, and Hard Place.
The “too much in winter” part does seem, however, to be in large part from coolant passing through the radiator — even though the thermostat should not be opening. You can tell that this is true by simply feeling the radiator on a cold day after a ride. It will be warm to hot, but it should be cold because the thermostat should be closed and should be saving that heat for the engine.
The “too little in summer” part can come from a lot of sources, mostly having to do with scale build-up in the radiator, or inadequate coolant flow through the radiator, or inadequate air flow through the radiator.
There would certainly be a loss of coolant flow through the radiator if the bypass hole is reduced in size, but relative to the hole made when the thermostat actually opens this would be very small. I don’t have actual measurements available, but from memory the bypass hole is pretty large, maybe 3/16", and the hole when the thermostat is open is an inch or better. If I were to reduce the bypass hole to 1/16" that would reduce the hole area from 0.00276 inches square to 0.000307 inches square, a factor of nine reduction which should help the winter situation quite a bit.
Now, if we look at the effect of this reduction on the open thermostat (summer) performance we have to consider the area of the “big” hole. Again, just guessing, let’s assume the main hole is one inch, and the stuff in the middle is one half inch. That gives us areas of 0.785 minus an area of 0.196 (for the center part), or a total open area of 0.589 plus 0.00276 for the original bypass hole or 0.59176 square inches total, and 0.589 plus 0.000307 for the area of the reduced bypass hole, or 0.589307 square inches total. This is a reduction in area of 0.4%.
Of course we need some real measurements here, and I’m using that bike every day to commute and don’t have the time to tear it down just now. Maybe next weekend. But a nine-fold reduction in excessive winter cooling vs. a 0.4% reduction in summer cooling looks like it might just be worth it. Also, there is the fact that the summer case may not be relevant if the problem with inadequate cooling is not restricted flow past the open thermostat but lack of radiator capacity or internal radiator scaling.