Overheating

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Re: Overheating

Post by outrgus »

cedric wrote:I've seen a few posts on KTMTalk about bad rad caps that don't hold the pressure correctly, might be worth trying another cap.
This happened with my brothers 300, he just bent the taps on the cap to hold tighter and fixed the issue. Worth a try.

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Re: Overheating

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How does the rad cap work and how does it relate to the over flow tube? Does the 1.8 (or 1.4 on my old 250) refer to how much resistance the cap will give before allowing boiling coolant to overflow?

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Re: Overheating

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cycleworks wrote:Im not sure Evans coolant is the best answer for overheating... kind of just masking a problem, right? Just my two cents....
I agree. Going with a higher boiling point or a stronger rad cap could be masking the real problem. I boiled over earlier in the week and it was because my coolant wasn't at the proper ratio. Mine was more water than coolant and even though it dissipates heat quicker the boiling point was far too low.
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Re: Overheating

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install an inline water temp hose to see what your coolant is actually doing and if you have problems with a rad cap. You can pressure test your rad cap fairly easy. just plug the 2 holes and pressure it up radiator empty and see what pressure it pops at.

http://www.trailtech.net/25mm-inline-water-temp-sensor" onclick="window.open(this.href);return false;.

I installed this on my KTM Cr500. I raced at the CSMX track with 1 radiator on a 25c day. fairly high speeds but the honda stayed at 185F all day.

KTMs overheat, its what you get for performance and lightweight materials. *the KTM 250 is 2 lbs lighter this year!!* yes, but without a cost.
hydro clutches will make your engine overheat as its dead easy to make it slip as you have no feel when it is engaging.


Install larger radiators. install a fan. put on slower gearing so you do not clutch as much

yz250 2stroke, 1.4 rad cap, NEVER overheats.

I would love to see the temp differences on a KTM versus yz250 2stroke on the same ride. I bet it would be darn right scary.

I will never forgot KTM geiser hill about 5 years ago at porkies right off the start on the east side loop. Free facials for all!

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Re: Overheating

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Looks like it's the inner clutch gasket, the one Slavens talks about here in case anyone else is wondering why they're loosing coolant on a KTM 250/300: http://www.youtube.com/watch?v=aqF8Id6NIWA" onclick="window.open(this.href);return false;
This is the same gasket that blows out back behind the kickstand when pressure builds up in the crankcase - ususally, it sounds like, from a clogged crankcsae breather hose. It happend to me a couple years ago on my '06 250XCW.
Hard to believe KTM keeps using this gasket.
Can I buy a Cometic gasket in town anywhere? Anyone have experience with it? I don't see why I'd put another POS OEM in there.

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Re: Overheating

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Local shops can order the cometic one but likely wouldn't have it in stock.
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Re: Overheating

Post by shipfner »

Just ordered the thicker black gasket from Blackfoot Direct.

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RJHenry
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Re: Overheating

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shipfner wrote:How does the rad cap work and how does it relate to the over flow tube? Does the 1.8 (or 1.4 on my old 250) refer to how much resistance the cap will give before allowing boiling coolant to overflow?
Yes, exactly.

The rad cap guts are obviously a spring that holds a rubber gasket down onto a sealing face. The ratio of the spring force when compressed to the area of the gasket exposed to the coolant pressure determines the relative pressure differential necessary to lift the rubber gasket off the sealing face and allow "leakage" out through the vent hose on the side of the neck.

The rad cap rating expresses that relative pressure differential in bars, kg/mm2, or atmospheres (I cannot get a definitive answer on this - anyone have verifiable source?). Practically, it doesn't matter what units since 1 kg/mm2 = 0.9807 bar and 1 atmosphere (nominal absolute air pressure at sea level) = 1.01325 bar. The difference due to units is far less than variability in the manufacture of the rad cap spring.

Anyhooooo... The liquid inside your system will reach the boiling point at higher temperature if contained at a higher pressure, regardless of the mix - water, glycol, evans - they all boil at a higher temp if the pressure is higher. A rule of thumb is that each 1 psi increase in pressure = 3 degrees Fahrenheit increase in boiling point. At 5000 feet water boils at 203F, and 50/50 water/glycol boils at around 216F.

1 Bar = 14.5 psi, so a standard 1.1 rad cap will relieve pressure from the cooling system (and into the catch bottle or onto the ground) when the pressure in the cooling system reaches about 16 psi (a boiling point of around 260F/127C). This is recently confirmed by VPower's 2005 CRF450X with Trail Tech Voyager and temperature probe - it gurgled at length yesterday at 126C somewhere around 6000 feet of elevation under a beautiful atmospheric high pressure system. :)

A 1.8 rad cap will relieve when cooling system pressure reaches about 26 psi (a boiling point of around 290F/144C). :eek:

PRO:
1) This "solution" increases heat rejection by increasing the temperature differential between the radiators and the air flowing through them - so the coolant achieves a bigger temperature drop through the radiator (and the air a bigger temperature rise).
CONS:
1) This change (1.1 => 1.8) increases max operating temperature by 30F/17C.
2) This change increases cooling system pressure by 10 psi, or 60% above manufacturer's design, AND increases max operating pressure by 30F/17C.
So the stresses created by pressure are greater, and the strengths of all of the pressure containing parts (rads, hoses, clamps, casting, etc.) are reduced by the higher temperatures... and if a component fails the fluid inside is HOTTER AND UNDER GREATER PRESSURE when it sprays out on the ground, objects, animals, or persons in the surroundings.

See how I presented that completely objectively??? :lol:
shipfner wrote:Looks like it's the inner clutch gasket, the one Slavens talks about here in case anyone else is wondering why they're loosing coolant on a KTM 250/300:
Yeah, that might lead to overheating too. All of us will admit that the fan, bigger rads, impeller, evans, 1.8 rad cap etc. are sort of deck chairs on the Titanic at that point. :smirk:
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Re: Overheating

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RJH, what's your take on surfactant additives... :thinking:

I've boiled over my 14 TE 250 twice, once was definitely clutch abuse on a long climb, the other again a slow wheelspinning climb with little airflow.

I want to avoid a fan kit (weight $ complexity), so I deleted the thermostat ($3) of 3/4" rad hose to plumb it like the TC (MX) version, the other change was to add Water Wetter to the 50/50 premix (old school silicate free). I also have Evans onhand, not in the bike yet obviously it will boil at a higher temperature, but liquid does transfer far more heat than vapour!

Last ride no issues, but no real long slow climbs to test it.

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Re: Overheating

Post by shipfner »

Thanks RJH, the 30% of your explanation that I understand makes complete sense :)
Any 250/300 owners reading this should check out this 20+ page thread on ktmtalk: http://www.ktmtalk.com/showthread.php?t=491909" onclick="window.open(this.href);return false;
Sounds like this is a very common failure on this gasket and given the location of the coolant leak, you often don't see it until it's too late... silent killer. Looks like lots of people are preemptively replacing the OEM inside clutch gasket with the Comteic one. Pretty cheap fix for the peace of mind.
Hoping to take the head off tomorrow and see what kind of damage I did.

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Re: Overheating

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To continue on Mr Henry's engineer geek rant, the risk of a higher pressure rad cap is reduced at our riding elevations. A rad is designed to open at standard pressure (sea level), which is 14.7psi air pressure. So at sea level the rad cap starts to lift when the vapour pressure on the coolant side overcomes the atmospheric air pressure and the spring pressure. As atmospheric pressure at our riding elevations is 2.0-2.5psi less than standard pressure a typical rad cap will open at a lower pressure than designed. i.e. at 5000ft a 1.6 bar rad cap is very similar to a 1.4 bar rad cap at sea level.
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Re: Overheating

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350scott wrote:To continue on Mr Henry's engineer geek rant, the risk of a higher pressure rad cap is reduced at our riding elevations. A rad is designed to open at standard pressure (sea level), which is 14.7psi air pressure. So at sea level the rad cap starts to lift when the vapour pressure on the coolant side overcomes the atmospheric air pressure and the spring pressure. As atmospheric pressure at our riding elevations is 2.0-2.5psi less than standard pressure a typical rad cap will open at a lower pressure than designed. i.e. at 5000ft a 1.6 bar rad cap is very similar to a 1.4 bar rad cap at sea level.
Well... yes and no. The vapour pressure (and thus boiling point) is definitely reduced at elevation due to the lower atmospheric pressure and there are nice graphs to that effect:
Picture 4.png
5Fig2.gif
As a result, the maximum TEMPERATURE that a given rad cap will take the system up to is reduced at elevation. The cap still adds 3 degrees per psi of pressure, but starts from a lower baseline of boiling point in open atmosphere.

Continuing the example above - at sea level with NO cap the 50/50 mix boils at 225F but at 215F at 5000 Feet Elevation. Adding a cap increases the boiling point accordingly:
Capture.PNG
Capture.PNG (9.05 KiB) Viewed 876 times
So 350scott is 100% correct that the maximum temp achieved with a 1.6 cap at 5000 feet is similar to the maximum temp achieved with a 1.4 cap at sea level.

The PRESSURE difference, however, is still equal to the spring rating of the cap. Regardless of the atmospheric pressure of the surrounding air, the cooling system will operate at a gauge pressure equal to the cap rating, and the components of the cooling system will be subjected to that pressure difference as they work to contain it.
malcolmzilla wrote:RJH, what's your take on surfactant additives...
Surfactant additives are essential in a cooling system. The primary benefit is breaking the surface tension of the water which:
1) increases the "wetting" of the coolant passages (and maximizes conduction of of heat from the metal to the coolant and back to the metal)
2) prevents cavitation (premature "bubbles" that occur below boiling point due to pressure dynamics in the fluid) that can erode metals, particularly the water pump impeller.

As a complete aside.... my favorite coolant cavitation story is Cummins diesel engine wet cylinder liners from back in the day - six cast iron sleeves with the piston inside and coolant outside, mounted in the cylinder block. The liner "rings" like a bell at each compression stroke "slap". The liner's vibration was so quick that it would "move away" from the water and, in the absence of surfactant additives, leave a void which formed a bubble. When the liner oscillated back the bubble would implode and "suck" chunks of cast iron off of the outside of the cylinder liner. Eventually, the liners pitted through, but always on a perfect vertical directly in line with the crank/con-rod rotation plane. When surfactants were added... no more pitting. Cylinder liner life went from 50 hours to 10,000+. This is totally irrelevant in dirt bikes, which do not have a cylinder liner, instead using a bored "block" with coolant passages cast into it.
malcolmzilla wrote:I want to avoid a fan kit (weight $ complexity), so I deleted the thermostat ($3) of 3/4" rad hose to plumb it like the TC (MX) version, the other change was to add Water Wetter to the 50/50 premix (old school silicate free). I also have Evans onhand, not in the bike yet obviously it will boil at a higher temperature, but liquid does transfer far more heat than vapour!
My understanding is that 50/50 already has enough surfactants (along with corrosion inhibitors and additives to reduce mineral depositing) that water wetter offers minimal additional benefit. Water Wetter is really intended to allow use of pure (deionized or distilled) water (which has the best heat transfer properties when undiluted) for use in hot climates with no risk of freezing - or in a seasonal application where the operator understands the need to take protective steps come fall! Red Line Synthetic does make a SuperCool coolant, but it has no anti-freeze - it looks like basically pure water with water wetter added, for double the money!

I caution against the removal of the thermostat. The flow restriction is minimal (and more than compensable with an upgraded impeller) and the thermostat is very important in maintaining a MINIMUM temperature in the engine. As much as we do not want the engine too hot, we also do not want to have cycles of hot and "cold" as we climb hills and descend hills. Heat cycling like that results in thermal expansion and contraction which is very unsettling for clearances (like piston rings) and precision fits (like head gaskets and case gaskets). Taxicabs last a million miles in part because they have less thermal cycles.

The TC (MX) version has a piston replacement recommendation of... 45 hours? No thermostat is a piece of that puzzle. Your bike is intended to last a lot longer than that, and is built differently as a result.

Another nice (if admittedly tangential) corollary is that you can buy the same Cummins engine block found in a Dodge Ram for services like Marine and Fire Truck with FACTORY outputs over 600 HP, but in a generator application you cannot get over 300 HP. The service life (in hours) expectations of a prime power generator vs. a fire truck are very different - as are the warranty terms.

In my experience, many of the changes discussed in this thread are incremental improvements at best. Removing the thermostat, switching to pure water (with wetter), upgrading the impeller, and increasing the rad cap each provide a SMALL increase in heat that gets moved to the radiators - but the real problem is transporting that heat away from the motorcycle. Bigger rads and/or more airflow are the surest ways to substantially improve cooling system heat rejection capacity.
Last edited by RJHenry on Wed Jul 23, 2014 10:32 am, edited 2 times in total.
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Re: Overheating

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RJHenry wrote:So 350scott is 100% correct
I figured I would clip this right away and get it over with... :D

Context is so important... sigh... :smirk:
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Re: Overheating

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RJHenry wrote:
RJHenry wrote:So 350scott is 100% correct
I figured I would clip this right away and get it over with... :D

Context is so important... sigh... :smirk:
You make me laugh. Also, you continue to give me faith that I'm not always the biggest geek in the room. And you're actually 107.36% correct.
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