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Old April 12th, 2019, 05:57 AM   #1
Ponr
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Thermostat operating temp

Hi I have a 250 and I noticed that it is overheating and I am looking at the thermostat. this thermostat does not open until 180į I see in the manual it says that it should open from 150 for the 160. I didnít know if maybe I have a higher temp thermostat.

Has anyone ever tested there thermostat?
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Old April 12th, 2019, 07:01 AM   #2
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I saw your earlier post about your EX250 overheating while stationary.

When vehicle engineers put a motorcycle (like the EX250) together they're working within a relatively narrow give-and-take situation that ends up producing a carefully balanced cooling equation. The performance of the bike's coolant pump (how many liters-per-minute it moves) and the size of the radiator is matched to the heat load the engine produces, and the make-or-break balance is most delicate at idle RPMs.

You can't just dial up the idle and expect that the bike can handle it.

Here on the forum it's not uncommon to see somebody getting overheating issues in stop-and-go traffic. In these cases the owner almost always admits that the bike is set to an idle speed that is higher than the Kawasaki Service Manual recommended level.
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Old April 12th, 2019, 07:29 AM   #3
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@greg737 has a point. On the other hand, I've purposely idled my 250 in the driveway to check the cooling fan, and found that it does not overheat. The fan cycles on and off, and I watched the temperature gauge needle moving higher and lower repeatedly with that cycle. Was your engine idling at a higher than normal speed at the time as Greg mentioned?

Maybe someone here has experience with the thermostat temperature ratings, but the manual says to replace the thermostat if it opens outside of the range of 146F to 152F.
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Old April 12th, 2019, 08:07 AM   #4
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Thank you Both for replying. It idles 1600-1700 only when on the tilted kickstand and idles find when straight. Iím thinking it due to the floats in the carburetor being tilted a bit causing it to possibly get running a little lean.


The t-stat is opening out of spec so Iím going to replace.
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Old April 12th, 2019, 12:58 PM   #5
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What you can also do is use lower-temp thermoswitch for fan so it comes on earlier. That way, up/down cycle is centred over lower mid-point temp.
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Old April 12th, 2019, 07:06 PM   #6
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Quote:
Originally Posted by Ponr View Post
I didn’t know if maybe I have a higher temp thermostat.

Has anyone ever tested there thermostat?
I think it's more likely you have a thermostat that's beginning to fail.

If you're prepared to go as far as removing the thermostat to do something like testing it in hot water you should just go ahead and replace it. Your bike is a 2004 so the thermostat is 15 years old now, why wouldn't you just replace it?

Thermostats don't always fail in the same way, sometimes they stick closed, sometimes they stick open, sometimes they end up with a shortened range-of-motion (not going all the way open or not going all the way closed).

The truth of a vehicle thermostat is that it is a consumable item (like the chain and tires, etc.), which means it will absolutely have to be replaced occasionally during the life of the vehicle. We EX250 owners are lucky because the OEM thermostat installed in our bikes has a pretty long life, but it doesn't last forever.

Just replace it and ride, your bike will almost certainly be fine.
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Old April 12th, 2019, 07:38 PM   #7
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And...

Not to go off-topic or thread-jack but: The truth of the EX250 is that its cooling system design is from the Jurassic Era of motorcycle design and owners (of properly maintained EX250s) will tell you that their bikes are cold-blooded reptiles which rarely run at even half way up the temperature scale on the instrument panel (only climbing over half way when sitting in traffic).

I got tired of my EX250's cold blooded nature and I installed a ThermoBob unit on it. The ThermoBob is a cooling system upgrade which adds a feature that most, if not all, modern vehicles have these days. It adds in a small constant-flow bypass line that skips over the thermostat and radiator of the bike, plumbed into the return flow line post-radiator.
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Old April 13th, 2019, 06:34 AM   #8
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Quote:
Originally Posted by DannoXYZ View Post
What you can also do is use lower-temp thermoswitch for fan so it comes on earlier. That way, up/down cycle is centred over lower mid-point temp.
In theory.

In practice, you still have the same Qdot produced by the engine and the same Qdot removed by the radiator, so overall, you'll get a thermostat that opens earlier, causing slow warm ups, and then you'll reach the same operating temp once everything gets to equilibrium. Once you move to a low enough rated thermostat temp that the rated temp is below the natural equilibrium temp of your engine and radiator, it literally just sits open and does nothing. Thermostats will regulate an operating temp higher by going to a higher temp range, not lower by going to a lower temp range.

Ideally, a cooling system gets your engine evenly up to temp as quickly as possible, then maintains perfect operating temp for all duty cycles. Obviously this isn't possible with old school mechanical parts, but between a bypass, a proper thermostat temp, and carefully sized bypass flow to avoid temp oscillations and shock when the thermostat opens, one can get darn close. Conveniently, the thermobob makes this a solved problem.

TBH, no 250 should ever be overheating unless there's a problem. The radiator is very large, relatively speaking.

Quote:
Originally Posted by greg737 View Post
And...

Not to go off-topic or thread-jack but: The truth of the EX250 is that its cooling system design is from the Jurassic Era of motorcycle design and owners (of properly maintained EX250s) will tell you that their bikes are cold-blooded reptiles which rarely run at even half way up the temperature scale on the instrument panel (only climbing over half way when sitting in traffic).

I got tired of my EX250's cold blooded nature and I installed a ThermoBob unit on it. The ThermoBob is a cooling system upgrade which adds a feature that most, if not all, modern vehicles have these days. It adds in a small constant-flow bypass line that skips over the thermostat and radiator of the bike, plumbed into the return flow line post-radiator.
BINGO! This right here. It legitimately makes a difference in how the engine operates in all temp ranges. It becomes problem free and does exactly what you expect it to do. No more cardboard needed on cool days.

The data speaks for itself:
https://shop.watt-man.com/Thermo-Bob...EARS-TB3-N.htm
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Old April 13th, 2019, 09:33 AM   #9
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A Thermo-Bob may be nice, but it's not necessary to install that system just to keep the bike from overheating. I've run the stock system for several years since getting my '05 250 and have never had any cooling problems.

Let's see what Ponr says about the cooling system performance when he replaces the faulty thermostat.
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Old April 13th, 2019, 11:16 AM   #10
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Quote:
Originally Posted by Triple Jim View Post
A Thermo-Bob may be nice, but it's not necessary to install that system just to keep the bike from overheating. I've run the stock system for several years since getting my '05 250 and have never had any cooling problems.

Let's see what Ponr says about the cooling system performance when he replaces the faulty thermostat.
To be perfectly clear... I took pains to be very specific with my statements, I made it clear that I was broadening the topic in order to give a larger (and true) perspective/overview of the EX250 cooling system.

I thought my description of the situation was clear, I said, "... owners (of properly maintained EX250s) will tell you that their bikes are cold-blooded reptiles which rarely run at even half way up the temperature scale on the instrument panel"

So I was not, in any way, saying that an EX250 owner would need install a ThermoBob in order to keep the bike from overheating.

The ThermoBob has the beneficial effect of: 1. it allows the engine to warm up more quickly, 2. it promotes and maintains a much more even thermal gradient across the entire water-jacketed cylinder liners and the cylinder head, 3. its constant flow of bypassed coolant promotes stability and more gentle temperature swings in the moments when the thermostat changes position (when the radiator flow of cooler water ramps up or ramps down).

Installing a ThermoBob along with a 195 degree thermostat will give the EX250 much better thermal characteristics across its operational envelope, from warm-up to stable cruising, and this combination does not affect/will not reduce the maximum cooling ability of the bike's cooling system, because once engine temperature has reached 195 degrees the thermostat is 100% open so the engine temperature equation is reduced to just a heat-rejection factor of water pump output and total radiator surface area.

And, while running at any thermostat position less than full open, an engine temperature of around 195 degrees is a much more carb-friendly temperature for engine operation (than something around 175)
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Old April 13th, 2019, 09:38 PM   #11
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Quote:
Originally Posted by Triple Jim View Post
A Thermo-Bob may be nice, but it's not necessary to install that system just to keep the bike from overheating.
I too, explicitly said that a 250 should not overheat unless there's something wrong.

Quote:
Originally Posted by choneofakind View Post
TBH, no 250 should ever be overheating unless there's a problem. The radiator is very large, relatively speaking.
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Old April 14th, 2019, 06:24 AM   #12
Triple Jim
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Don't get all excited you two. I just made the post to be sure our relatively new member was not getting the idea the he needed to start the ThermoBob project right away. After all, the thread is about a possible overheating problem that may have been traced to a faulty thermostat, not about how to optimize the cooling system.
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Old April 14th, 2019, 02:50 PM   #13
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Quote:
Originally Posted by choneofakind View Post
In theory.

In practice, you still have the same Qdot produced by the engine and the same Qdot removed by the radiator, so overall, you'll get a thermostat that opens earlier, causing slow warm ups, and then you'll reach the same operating temp once everything gets to equilibrium. Once you move to a low enough rated thermostat temp that the rated temp is below the natural equilibrium temp of your engine and radiator, it literally just sits open and does nothing. Thermostats will regulate an operating temp higher by going to a higher temp range, not lower by going to a lower temp range.

Ideally, a cooling system gets your engine evenly up to temp as quickly as possible, then maintains perfect operating temp for all duty cycles. Obviously this isn't possible with old school mechanical parts, but between a bypass, a proper thermostat temp, and carefully sized bypass flow to avoid temp oscillations and shock when the thermostat opens, one can get darn close. Conveniently, the thermobob makes this a solved problem.
Fan thermoswitch is not same thing as thermostat.
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Old April 15th, 2019, 08:07 PM   #14
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Quote:
Originally Posted by DannoXYZ View Post
Fan thermoswitch is not same thing as thermostat.
The irony of my poor reading there is not lost on me, no worries. I missed the switch part completely.
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