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1995 kawasaki vulcan en500. My bike has been over heating. On a short ride the other day it started spewing radiator fluid. Today I took the radiator off. Gave it an at home pressure test by blowing on it, found no holes. And then flushed it. Once reassembled, I added coolant to the radiator and the coolant reservoir. Then turned the bike on and let it idle. After 10 mins of idling the temperature light turned on and the coolant resevoir began to fill up and overflow. Turned the bike off and in a couple minutes the coolant resevoir emptied back down to the normal level. I did not notice any leaks anywhere else then when the coolant overflowed. The fan is working fan and turns on after a few minutes of idling. The hoses are old but do seem to be in good condition.

Thanks for any insights
 

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Being not at all familiar with that model, I have to wonder -- is there a thermostat? Your symptoms are identical to those demonstrated by several cars I've fooled with over the years that turned out to have a thermostat stuck shut. I've also experienced thermostats stuck open, leading to an engine that took forever and a day to reach operating temperature.

If there's a fan, it could also be a bad switch that keeps the fan from kicking in when it should. Usually, that's when the bike is sitting still with no airflow through the radiator.
 

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Hello,
You need to replace your thermostat and your temperature switch, since boil over occurred. Also have your radiator cap tested.

Sent from my SM-G903W using Tapatalk
 

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The water pump could have stopped pumping, too; or, there could be an air pocket around the fan switch, making it come on later than it should.. Try this: lift the front, or roll the front wheel up on a brick - use something to stabilize the bike in the upright position. With the engine cold, start the bike and, as it warms, feel the radiator; it should begin warming from top to bottom, as the thermostat opens, and hot water begins to flow. After a while, it should be about the same temperature from top to bottom. If that is true, the pump and thermostat are working; of course,the pump could be weak, but that would be a less common failure mode.

As the engine gets hotter, and the coolant begins rising in the return bottle, any air should be pushed along with it. A rev or two should help. The fan should come on soon, and cool it back down.
 

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Did you get any "crap" out of the radiator when you flushed it out? If you did, there's going to be crap in the engine too. Did you "burp" your radiator when you reassembled everything?

When everything is cold, start the engine and let it idle again. Now I'm going to assume you can feel your radiator. As it heats up, is it all over evenly, or is it heating up only on one side, or only in the middle, something like that? I think it should heat from the top down. But there shouldn't be any "cold" spots.
Your radiator may pass a pressure test but some tubes may be clogged up inside.

Your hoses may look okay, but when the engine warms up, and the thermostat opens, as coolant starts flowing through one hose, it can create a vacuum that will cause an old hose to collapse, slowing the normal flow.

Thermostats are cheap, (or they used to be) you might just replace it and cure your problem. If you don't know how old the parts are, I think I would start with the hoses and thermostat.
I'd save the water pump for last.

If I've told you anything wrong, someone will be along shortly to make a correction.
 

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I'm pretty sure your bike has the same engine as mine.




Does this look at all familiar?

What your describing, 9 out of 10 times, ends up being a warped head. Sometimes described as a blown head gasket. But technically you can't "blow" the head gasket on these engines. The fix is not expensive, but is quite involved. I could get you some info on it if need be.
 

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Discussion Starter #7
I'm pretty sure your bike has the same engine as mine.




Does this look at all familiar?

What your describing, 9 out of 10 times, ends up being a warped head. Sometimes described as a blown head gasket. But technically you can't "blow" the head gasket on these engines. The fix is not expensive, but is quite involved. I could get you some info on it if need be.
Yes this is the same engine. I am waiting the new thermostat in the mail. I am going to replace hoses. And then if that doesn't work the head gasket is probably the issue. Thankyou. Will keep you updated
 

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Discussion Starter #8
Did you get any "crap" out of the radiator when you flushed it out? If you did, there's going to be crap in the engine too. Did you "burp" your radiator when you reassembled everything?

When everything is cold, start the engine and let it idle again. Now I'm going to assume you can feel your radiator. As it heats up, is it all over evenly, or is it heating up only on one side, or only in the middle, something like that? I think it should heat from the top down. But there shouldn't be any "cold" spots.
Your radiator may pass a pressure test but some tubes may be clogged up inside.

Your hoses may look okay, but when the engine warms up, and the thermostat opens, as coolant starts flowing through one hose, it can create a vacuum that will cause an old hose to collapse, slowing the normal flow.

Thermostats are cheap, (or they used to be) you might just replace it and cure your problem. If you don't know how old the parts are, I think I would start with the hoses and thermostat.
I'd save the water pump for last.

If I've told you anything wrong, someone will be along shortly to make a correction.
I will burp the radiator in the morning. thankyou. I have a new thermostat coming in the mail and I will change the hoses tomorrow. Thankyou will keep you updated.
 

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Does the coolant overflow, and/or overheat, if you start the bike then go for a ride after a brief 1 ~ 2 minuet warm up?
If it does I'd suspect a bad radiator cap, or as already suggested possibly a bad.thermostat.

Although, unless your'e in a very cold climate I''m thinking 10 minutes of idling is too long to let a bike sit and run.
Even though your EN has a radiator and a fan, foreword movement is still required for cooling.
The cooling fan alone is not adequate for cooling the radiator and engine all by itself. It's really more for minor slow downs and such along the road.
If you're hopelessly stuck in stop and go traffic on a hot day... the fan is not much more than a last ditch effort while you search for a place to stop and cool.
The bike needs to be in the wind. It ain't like a car's cooling system.

S F
 

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You can test the old thermostat by looking at it and making sure it is closed at room temperature. Then placing it in a pot of water on a stove, suspending it in the middle of the water (not letting it touch the bottom of the pan). You can feed a wire through a hole on the outer edge of the thermostat to achieve this. Also need a thermometer held in the water in a similar way (not touching the bottom of the pan) . Turn the heat on and watch the thermostat, when you see it open the thermometer should read between 177f - 182f.

I suspect that even if you do have a bad thermostat and replace it, you are still going to have the same problem. Although certainly doesn't hurt to check. If the head is warped, then the damage is done, and correcting what ever caused the initial over heating wont fix it. The most common cause I have seen for this to happen is to run the bike near, at, or above red line for as little as a few minutes. Even keeping it as low as 9500 rpms for as little as 10 or 20 minutes has proven problematic. If you have always kept your rpm's well below this, I may be inclined to think you have a slight possibility that the head is not warped. Unless you ever removed the head for any reason.

My best advice right now is if you haven't already done so, you should get a factory service manual.
 

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Discussion Starter #11
Hmm
Does the coolant overflow, and/or overheat, if you start the bike then go for a ride after a brief 1 ~ 2 minuet warm up?
If it does I'd suspect a bad radiator cap, or as already suggested possibly a bad.thermostat.

Although, unless your'e in a very cold climate I''m thinking 10 minutes of idling is too long to let a bike sit and run.
Even though your EN has a radiator and a fan, foreword movement is still required for cooling.
The cooling fan alone is not adequate for cooling the radiator and engine all by itself. It's really more for minor slow downs and such along the road.
If you're hopelessly stuck in stop and go traffic on a hot day... the fan is not much more than a last ditch effort while you search for a place to stop and cool.
The bike needs to be in the wind. It ain't like a car's cooling system.

S F
I never knew that. I do live in hawaii so it is very warm. I have a new thermostat and new radiator cap on the way so am eager to see how that works. Thankyou.
 

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Discussion Starter #13
I do
Does the coolant overflow, and/or overheat, if you start the bike then go for a ride after a brief 1 ~ 2 minuet warm up?
If it does I'd suspect a bad radiator cap, or as already suggested possibly a bad.thermostat.

Although, unless your'e in a very cold climate I''m thinking 10 minutes of idling is too long to let a bike sit and run.
Even though your EN has a radiator and a fan, foreword movement is still required for cooling.
The cooling fan alone is not adequate for cooling the radiator and engine all by itself. It's really more for minor slow downs and such along the road.
If you're hopelessly stuck in stop and go traffic on a hot day... the fan is not much more than a last ditch effort while you search for a place to stop and cool.
The bike needs to be in the wind. It ain't like a car's cooling system.

S F
I do notice a small crack in the coolant resevoir right next to the low indicator. Could this be an issue?
 

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You can test the old thermostat by looking at it and making sure it is closed at room temperature. Then placing it in a pot of water on a stove, suspending it in the middle of the water (not letting it touch the bottom of the pan). You can feed a wire through a hole on the outer edge of the thermostat to achieve this. Also need a thermometer held in the water in a similar way (not touching the bottom of the pan) . Turn the heat on and watch the thermostat, when you see it open the thermometer should read between 177f - 182f.

I suspect that even if you do have a bad thermostat and replace it, you are still going to have the same problem. Although certainly doesn't hurt to check. If the head is warped, then the damage is done, and correcting what ever caused the initial over heating wont fix it. The most common cause I have seen for this to happen is to run the bike near, at, or above red line for as little as a few minutes. Even keeping it as low as 9500 rpms for as little as 10 or 20 minutes has proven problematic. If you have always kept your rpm's well below this, I may be inclined to think you have a slight possibility that the head is not warped. Unless you ever removed the head for any reason.

My best advice right now is if you haven't already done so, you should get a factory service manual.
The thermostat seems to be opening after about 5 mins of idling
 

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The thermostat seems to be opening after about 5 mins of idling
That isn't the test. But looks about right anyway. Very good odds you have a good thermostat. Probably end up having a good radiator cap also. You probably could have had the cap pressure tested at a radiator shop for less than buying a new one.
That crack in the coolant reservoir is not important at this time (unless it is leaking), but should be addressed after you work out the issue at hand. You could get a used one for cheap.
On the chance that the thermostat and radiator cap doesn't fix the issue, before buying a bunch of water pump parts. You can test the water pump by removing the radiator cap (when the engine is cool), crank the engine up, let it come to temperature, and when the thermostat opens you should see the water flow. But I doubt that the water pump is defective anyway.
Did you get the associated O-rings that go in the thermostat housing? If not, then you may end up with a leak (s) there when you change out the thermostat.

Keep us posted, I will give you more information later if you need it.
 
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