660 thermostat and fan - Yamaha Grizzly ATV Forum
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post #1 of 7 Old 01-22-2010, 12:53 PM Thread Starter
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660 thermostat and fan

I recently bored my 660 out .080. I would like to know what the stock opening temp is for the t-stat and what part number I could possibly find a lower temp under at a local parts store. Thanks.
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post #2 of 7 Old 01-22-2010, 01:26 PM
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The OEM thermostat for the 660 (Part # 5KM-12411-01-00 ) starts opening at 129 degF and is fully open at 158 degF which are industry standards. As for local parts stores, I don't think ones around here can help you. Trying to find one that fits at a lower range may be a problem.

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post #3 of 7 Old 01-22-2010, 02:29 PM
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USNY is correct. You need either Red-Line Water Wetter or Engine Ice to cool her down some. More and more brands are coming out and Evans and Be-Cool are choices as well. I have Engine Ice and it performed as stated, I'm happy w/it.

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post #4 of 7 Old 01-22-2010, 03:01 PM
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There is a little trick you can try. I used to do this on cars or trucks to help keep the temp down. Take the thermostate and drill a tiny hole on both sides of it. This way it will let the water threw without opening up fully,this will help keep it running cooler since you have a constant flow of coolant. Now, I can't tell you how big to drill them its just a trial an error thing. If you really want it to stay cool take the thermostate out. I wouldn't do that because it would probably run to cold and thats not good. I think the special coolant they have will work but probably not enough for your needs. Let me know if you try curious to see if works. I know it does for cars or trucks.
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post #5 of 7 Old 01-22-2010, 05:52 PM Thread Starter
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Yeah, I've drilled holes in thermostats before too. I have used the Be-Cool additive in my 73 Nova before also. Good stuff. I was hoping for a lower opening but 129 does not sound too bad. I'll have to order one I guess. Yamaha parts nation has one for $16.25 (not too bad).

What is the normal water temp on these things? I would imagine they would not need to get much hotter than 215-220 at the highest with new 50/50 coolant.
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post #6 of 7 Old 01-22-2010, 05:57 PM
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I took my t-stat out and gutted it. I took the spring and all out and just put the outer piece back in to act like a restricter and it brought my temps down by 10-15 deg f.

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post #7 of 7 Old 01-23-2010, 12:35 PM Thread Starter
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That's a good idea too.
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