overheating issue - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 8 (permalink) Old 08-26-2017, 03:50 PM Thread Starter
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overheating issue

gauge says overheating.but no pressure builds up in system.nothing is going into overflow.i can take radiator cap off while it says hot.and stick my finger in coolant.it's hot.but not as it would be if it was as hot as gauge says.i have backflushed.clear water comes out head holes.out of radiator.i have removed hoses up top and sprayed water down through them.water comes out head holes clean and hard.so there's no obstructions in coolant system.has a new thermostat,new temp sensor,new impeller,new starter.it won't start after shutting it off,until you let it sit around fifteen minutes.so i'm confused.if it is hot as gauge says.then coolant would be boiling over into overflow tank.cap would explode off when I take it off being so hot.but none of that happens.but yet it won't start back up acting like it's hot.i can keep cap off.and watch coolant begin to flow when thermostat opens.so I know it's moving.fan is wired up to a toggle switch so I leave it on.so the fan works.and radiator looks new.no obstructions.anyone run into such a thing?it's an o3 seven fifty Vulcan.and yes,i have burped the air out by using the bleeder.many times.coolant always begins coming out.no air.thee only thing I can think.is maybe water pump impellers not moving.but is that possible.from looking in manual.it sits on a shaft that has to move.if it was off of shaft or broken,i'm sure youd know it.or it looks like theres no room possible for it to come off shaft.and again.i can see coolant moving when stat opens.and previous owner I have met recently as I was out and about.he told me he had same prob and put new impeller and starter on and couldn't figure this out.


Last edited by Jr Mullins; 08-26-2017 at 03:54 PM. Reason: needed to add more about issue.
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post #2 of 8 (permalink) Old 08-26-2017, 05:34 PM
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Could be some hard blockage in the radiator cores. It's a small radiator so it wouldn't take much to reduce the efficiency.

Rolling 30-35 mph should be enough to cool without a fan, so that makes low coolant flow in the radiator core more of a possibility.
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post #3 of 8 (permalink) Old 08-26-2017, 05:36 PM
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Sorting through your post again ..... It might pay to check the radiator with an IR temp gun to see what the temp actually is. Check all over the radiator to see if the temp is consistent or has hot/cold spots.
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post #4 of 8 (permalink) Old 08-26-2017, 08:43 PM
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head gasket.maybe pressure isn't building cause its being released into cylinder.going out on a limb here.

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post #5 of 8 (permalink) Old 08-26-2017, 11:37 PM Thread Starter
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I wondered about that.so I put water hose in top hose input.water flows strong out bottom hose.crystal clear to.not a hint of scale or any chunks like from additives.i sprayed hose through fins.comes straight out back with no dirt or bugs or anything like if it was jammed up in fins.all fins straight as a new one.thank you though for the suggestion.

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post #6 of 8 (permalink) Old 08-26-2017, 11:40 PM Thread Starter
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well I don't have the temp gun.but I took a thermometer.stuck it in filler neck and watched it.it stayed at one sixty degrees with fan running.thermostat didn't open.so I shut fan off.then could see raising coolant so thermostat opened.it began spilling out.temp of coolant then was around 180.but gauge on bike was over in hot zone.

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post #7 of 8 (permalink) Old 08-27-2017, 02:30 AM
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Quote:
Originally Posted by Jr Mullins View Post
well I don't have the temp gun.but I took a thermometer.stuck it in filler neck and watched it.it stayed at one sixty degrees with fan running.thermostat didn't open.so I shut fan off.then could see raising coolant so thermostat opened.it began spilling out.temp of coolant then was around 180.but gauge on bike was over in hot zone.
what type of thermometer are you using? the reason I'm asking is I am a cook,and the thermometers I use in ny trade need to be calibrated once in a while.

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post #8 of 8 (permalink) Old 08-27-2017, 12:11 PM
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I think you've probably got a bad temp sending unit (on the thermostat housing), as shown by the thermometer and your ability to stick your finger into the coolant when the dash gauge is completely in the red zone and pegged. Your finger should come out like a boiled hotdog if the coolant was really 220į.

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