Cooling and Overheating Dangerously - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 8 (permalink) Old 02-22-2017, 10:50 AM Thread Starter
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Cooling and Overheating Dangerously

Hey Guys,
I just purchased a 1991 750 it has 8,000 miles on it. I'm having a problem with the cooling system. I will start the bike let it warm up but it will over heat. Then when I start rideing it cools to almost dead cold like it's been turned off for hours. I was just wondering what this sounds like to you guys.
My thoughts are a bad thermostat and a bad fan switch or fan. My other question is how would I test the fan switch and fan without flushing my coolant.
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post #2 of 8 (permalink) Old 02-22-2017, 12:18 PM
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bad fan/fan switch, bubble of air in cooling system, or thermostat. 'bout only thing that can do what your describing.

on a side note: I dont let my bike idle for warmup much more than 30 secs or a min.. when idling, the water pump is not moving coolant at its most effecient, and the charging system
is barely putting out enough grunt to charge the battery with out fan on.

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post #3 of 8 (permalink) Old 02-22-2017, 12:29 PM
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I'm kinda curious if it still has the original thermostat and maybe even original coolant. '91 is a long time ago but 8K miles is really nothing. Mine is an '06 and its a one-owner: me. Just this past season I finally changed out the original coolant. It only had a smidgen over 11K miles on it and had also sat for a few years. The thermostat still looked good and I hadn't been having any cooling issues but I changed it out anyway, along with all of the hoses (five). I did the distilled white vinegar flush and put in Engine Ice coolant. It runs cooler now but, as I said, wasn't running bad to start with. I just felt better KNOWING everything was fresh. You never know if-or-what kind of crud is floating around inside until you flush it. Parts for the system are available but I'm not the person to tell you how to go about testing it. I know you'll feel better when it is all corrected.

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post #4 of 8 (permalink) Old 02-22-2017, 02:00 PM
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Just touch a ground wire to the fan switch and it should run, even with the key off. You should still check for normal operation when the temp hits about midway on the gauge.

Sounds like the thermostat is stuck open or has been removed.

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post #5 of 8 (permalink) Old 02-22-2017, 09:59 PM
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I had this problem last summer. The fan is super easy to check. Like Spockster said, all you have to do is ground out the single wire on the fan switch. The bike doesn't even have to be on. If the fan is still good then it will come on when you ground out that wire.

The next thing would be to see if the fan comes on when the bike gets hot. If it does, then look at the thermostat. If it doesn't, then you need a new fan switch. They are expensive, but sometimes you can find used radiators on eBay for less than $40 and they will normally include the fan switch.

Good luck!
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post #6 of 8 (permalink) Old 02-22-2017, 11:30 PM
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With the engine cold, take the radiator cap off. If the radiator is full to the top, take a small amount of coolant out so the cores are just covered. Start it up cold and rev it a little while watching the coolant. If the coolant is circulating as soon as you start it, the t-stat is stuck open or has been removed.

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post #7 of 8 (permalink) Old 02-22-2017, 11:39 PM
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my fan never came on when the bike was moving. then when the fan switch crapped out I wired it to a switch.easy.just wire a switch and ground other side

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post #8 of 8 (permalink) Old 02-23-2017, 08:32 AM
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Or buy a sportster like mine which is faster than the very light of day.

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