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Discussion Starter #1
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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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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Discussion Starter #4
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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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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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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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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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*
 

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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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Discussion Starter #10
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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Whadda mean not elegant? Actually it looks very finished. I might even put studs along the radiator sides. I used a naughahyde type black material with a stiff panel inserted in a 'pocket' (slips into the hemmed areas top and bottom to hold it in place).
Might even put a Fire and Steel emblem on the front *G*
Now if I had wedged a flattened 12 pack carton in there then you could say.. 'not elegant', but I'd still be riding!
 

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Dianna, I am so sorry! Please accept my humble apology for the “not elegant” comment. I was thinking of the engineering, not the style . . .

But, you know some six-pack cartons are pretty fancy . . . in fact the fanciness seems to be inversely correlated with the quality of the beer. The Budweiser carton, for example, comes to mind for a very fancy radiator decoration. I’ve never seen a Newcastle Brown carton because I get mine on tap, but I bet it is fairly plain judging from the quality of the brew.
 

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I believe in giving credit where credit is due and I gfot my idea from gYpSy's site. just modified it a little. http://ourworld.cs.com/moonmist115/toocold.html
The engine now runs a bit warmer.. not close to the summer but warmer than without the blocking.
If you think of the marks as // | \ with the | being the thermometer one, I now run about // * | \, (where the * is) In the summer I tend to run// *| \
using the water wetter unless I get stuck in traffic then of course it climbs but not into the red
 

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That's better than me, with the temp about 50 and cruising around town without hot-dogging too much my temp stays about half way between the first two marks. Which is too cold! The bike seems to run just fine though.

I'm going to look into the by-pass line idea when I can. So far I'm thinking I can plumb into the temperature sensor port with a "T" fitting, and make a return fitting just ahead of the radiator return. Then I'll block off the bypass hole in the thermostat completely and run a quarter inch line between fittings.

I stopped at an auto parts place yesterday and just looked at the theromstats there, and not a one had a bypass hole at all that I could see. They were in blister packs though, and I couldn't see them very well.

Bill
 
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