Radiator Performance - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 18 (permalink) Old 06-03-2012, 11:01 PM Thread Starter
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Radiator Performance

My bike very slowly runs hotter and hotter in the summer. I'm limited to 90 minutes of riding because that's when it starts to get into the red. The warm up is very slow.

Testing temp with an IR thermometer I'm showing 250F at the thermostat housing, about the same at the top of the radiator and varying between 160F-200F at the bottom of the radiator when the gauges reads on the edge of the red (bike idle, fan on) (IR readers can be a bit finicky so some of the variation could be the instrument). I'm thinking about taking the radiator to a radiator shop for a rod out. The bike was left sitting for some time before I got it. I installed a new OEM thermostat about a year ago. Based on the temps provided does it sound like the radiator is cooling properly?

-Robert
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post #2 of 18 (permalink) Old 06-03-2012, 11:10 PM
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Have you ever done a good rad and system flush,changed coolant? Like on a car can be a lot of things to cause what you describe. A simple air bubble can cause problems if not purged correctly. Can also go to a 75% water and 25% coolant mix seems to help!

04-3,200 miles bought July 2011 with 928 miles. Loaded with acessories to many to list here, see my albums for more details! I also make a custom tank bib specific for the 750 if anyone is interested, ck my albums for some pics.
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post #3 of 18 (permalink) Old 06-03-2012, 11:16 PM Thread Starter
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Originally Posted by romeobravo172 View Post
Have you ever done a good rad and system flush,changed coolant? Like on a car can be a lot of things to cause what you describe. A simple air bubble can cause problems if not purged correctly. Can also go to a 75% water and 25% coolant mix seems to help!
Thanks. On a car I get air bubbles out by running high RPM. The bike has been running like this for awhile and I do go up pretty high on the RPM during acceleration. Is there anything else I can do to push out any bubbles? (I did think about bubbles but figured I'd run enough high RPM that it may not be an issue).

Hmmm, I just noticed in the service manual that there is a procedure for bleeding air out of the system using the bleed nipple. Could it be that I have air in the system after multiple rides? Is the air that stubborn? I guess I'll try their bleeding procedure.

-Robert

Last edited by RobertGary1; 06-03-2012 at 11:22 PM. Reason: read the manual
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post #4 of 18 (permalink) Old 06-03-2012, 11:26 PM
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On your thermostat housing there is a bleeder valve on the top to do that, not much difference in height than the fill cap, think trick is to fill (say after flush or fluid change) very slowly!!! Someone posted on here great pics on doing a coolant drain and change, ck that out. Think there is about 5 drain plugs to do it.

04-3,200 miles bought July 2011 with 928 miles. Loaded with acessories to many to list here, see my albums for more details! I also make a custom tank bib specific for the 750 if anyone is interested, ck my albums for some pics.
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post #5 of 18 (permalink) Old 06-07-2012, 01:25 AM Thread Starter
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Well I bleed the system but got no air bubbles. Bike is still very slowly getting too hot. Next step will be to remove the new thermostat and see if it still gets too hot without the thermostat. If that test doesn't work the next step will be to rod out the radiator. I'm still limited to 90 minute rides in the summer.

-Robert
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post #6 of 18 (permalink) Old 06-07-2012, 08:46 AM
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Sounds like your temp sensor is bad. Everything sounds like it is working in the proper heat range. If you remove the thermostat it will run cooler, not hotter. make sure you do a good system flush.
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post #7 of 18 (permalink) Old 06-07-2012, 08:51 AM
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Is it possibly the thermostat was installed backwards? I hate to admit it but I've done that on my truck once.

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post #8 of 18 (permalink) Old 06-07-2012, 12:46 PM Thread Starter
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Quote:
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Sounds like your temp sensor is bad. Everything sounds like it is working in the proper heat range. If you remove the thermostat it will run cooler, not hotter. make sure you do a good system flush.
IDK. 250F seems really hot. Even for a modern car with emissions, etc that would be hot.
You are correct, the purpose of removing the thermostat is to see if the bike no longer overheats. If it does, that indicates a restricted thermostat.
I think that there is a lot of long term benefit of a system flush, but for the purpose of solving any specific mechanical issue I think its snake oil. The only part of the cooling system narrow enough to actually plug up is your radiator and a plugged up radiator vein can't be flushed because it has no flow. In my experience the only way to correctly fix a plugged radiator is to remove the top and bottom and rod it out. Fortunately we have a couple shops near here that do that all day long. Good welders.

-Robert
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post #9 of 18 (permalink) Old 06-07-2012, 06:30 PM
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250 is to hot, there is some sort of restriction in your system. I read wrong, I thought you said it was running about 160-200 and the gauge was reading 250.
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post #10 of 18 (permalink) Old 06-07-2012, 08:13 PM
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One thing I haven't seen anyone touch base on, Take a light and shine it through the backside of the radiator while looking through the front to make sure the cooling fins aren't clogged up with road grime and dead bug parts. Radiator gets more flying debris than anything on the bike.

Last edited by Chuck A.; 06-08-2012 at 01:45 PM.
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