Engine Temperature - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 15 (permalink) Old 11-26-2005, 01:10 AM Thread Starter
Dan
 
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Engine Temperature

I have a 2005 VN750 with 3500 miles. When I ride it on a cold day, about 40 degrees, the engine barely warms up even after 20 or 30 miles. The temperature barely moves, it just comes slightly off the peg. Although when I idle in traffic the engine gets considerably warmer. Does anyone think the thermostat might be stuck open? Does anyone else have an engine that stays real cold in cold weather? I'm not sure what to do.
Thanks,
Dan - Seattle
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post #2 of 15 (permalink) Old 11-26-2005, 07:12 AM
 
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Re: Engine Temperature

It doesn't sound like you have anything wrong. The engine is getting air-cooled when you're moving, and water-cooled when you're idling in traffic.

My Vulcans seldom show much on the heat gauge either, even down here in a warmer climate.

CD in Frederick, OK
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post #3 of 15 (permalink) Old 11-26-2005, 12:20 PM
 
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Re: Engine Temperature

Sounds OK to me, In the mornings when I was still riding to work my temp guage didn't move much either when the temp was below 40, below 30 it would cool all the way down at hiway speeds. Thing about building something to block off half the radiator for late winter/early spring riding until the nightime lows get up to the mid-forties.
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post #4 of 15 (permalink) Old 11-26-2005, 01:43 PM Thread Starter
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Re: Engine Temperature

Thanks Ol Poop and Woody. I think I will experiment with covering part of the radiator and see what happens.
Dan
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post #5 of 15 (permalink) Old 11-27-2005, 12:39 PM
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Re: Engine Temperature

I have the same problem with a ‘99 model. I even tried replacing the thermostat, but nothing changed. And I can tell that the radiator is getting water flow even though the temp is low because it does get warm, so blocking part of it should work even if this is less than an elegant solution.

My car definitely doesn’t work like this, and the whole point of having water cooling is to keep the engine at a nearly constant temperature so that tolerances can be closer, etc. So, I’m thinking that Kaw has designed this machine with an improper thermostat. By improper, I mean that the hole in it that allows a “small” flow so that the thermostat can respond to a temperature increase is actually too big and provides significant cooling potential all by itself. Probably because the thermostat is the same one used on an automobile and has the flow for those engines.

When I can get around to it I’m going to take out the thermostat and see if I can either replace it with an automobile model the same size and temp range, but with a smaller flow-through hole, or try to block off the existing hole with a bolt or something and drill a new, smaller one.

Has anyone tried this?

Bill
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post #6 of 15 (permalink) Old 11-27-2005, 10:49 PM
 
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Re: Engine Temperature

I wouldn't mess with the factory setup if it were my bike just for the simple fact that these are not car engines tucked away in a engine bay. Remember this is a small engine exposed to the elements, airflow all the way around.Doesn't take much to keep them cool in cold weather. In the summer when it's 90 these engines sometime don't seem to have enough cooling system capacity unless you are moving at a good clip. Kinda like being between a rock and a hard place. Just my .02
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post #7 of 15 (permalink) Old 11-28-2005, 04:36 PM
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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.

Bill
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post #8 of 15 (permalink) Old 11-28-2005, 09:14 PM
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Re: Engine Temperature

I have a real simple solution. I use Water Wetter in my radiator for summer and during the cooler months I use a velcroed panel across the radiator (Attaches to the sides of the radiator cover with industrial strength velcro.
Easy to adjust for weather and not a lot of ride time wasted *S*

Dianna
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post #9 of 15 (permalink) Old 11-29-2005, 12:10 PM
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Re: Engine Temperature

Another consideration on the issue of changing the diameter of the bypass hole in the thermostat that occurred to me last night: if the bypass hole is smaller then the thermal response time will be longer. That is, if you “hit it hard” and heat up the engine suddenly, then the additional temperature will not be sensed by the thermostat thus causing it to open as fast, because the flow is slower.

Which suggests that the whole problem could be avoided entirely if there was a permanent bypass around both the thermostat and the radiator, but located close to the thermostat so it would sense the coolant temperature and respond.

Dianna’s way is certainly the simplest, but it sure isn’t very elegant.
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post #10 of 15 (permalink) Old 11-29-2005, 11:15 PM Thread Starter
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Re: Engine Temperature

I wonder if actually is detrimental to have the engine run so cold in the winter?
It seems like Kawasaki would have thought about this.
Dan
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