that is my question. it seems you would want consistent cylinder temps to ease the jetting chore. there have been 50 degree days where i have been on the gas running open fields (4and5th gear)for twenty min and whaaaaaa there is a fouled plug. the freaking cylinder is cold as ice and the radiator is cold too. the jetting is already lean. 168 from a stock 172 and 45 pilot from a 48. the motor likes the cold (dense) air. i dont think leaning it would be a good idea. seems the extra cold air from the speed is keeping the water in the radiator from coming up to temp. seems like a thermostat would be beneficial. i can get heat in the motor by blocking one of the radiators but this seems pretty low tech to me.
why dont 2 strokes use thermostats?
- Thread starter tx246
- Start date
CanadianRidr
Sponsoring Member
- Oct 22, 2001
- 2,021
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5 mins for a 2-stroke race bike like a cr,yz,kx is too long. It should be until you can feel the side of the cylinder warm through a glove:D
polyesterpig
Member
- Nov 21, 2001
- 24
- 0
gasket holes
If you remove a thermostat on a auto, most people think that it will run cooler. In reality, it will run warmer due to the engine cycling the coolant too fast and not letting the radiator do its job. Thus enlarging those holes in your gasket just might make your bike run hotter.
If you remove a thermostat on a auto, most people think that it will run cooler. In reality, it will run warmer due to the engine cycling the coolant too fast and not letting the radiator do its job. Thus enlarging those holes in your gasket just might make your bike run hotter.
Coolant flowing too fast to transfer heat is a myth. On a cold winter day, does the wind ever blow too fast to make you cold?
When a thermostat is removed, a restriction (large washer) is substituted to maintain pressure in the block and head.
Low pressure=low boiling point.
Low boiling point=steam pockets.
Steam=hot spots.
Hot spots=detonation.
Detonation=DNF
When a thermostat is removed, a restriction (large washer) is substituted to maintain pressure in the block and head.
Low pressure=low boiling point.
Low boiling point=steam pockets.
Steam=hot spots.
Hot spots=detonation.
Detonation=DNF
- Nov 25, 1999
- 7,926
- 43
In autos, thermastats are for the heater. Remove the thermostat, no heater. This allows the water temperature to reach the desired temperature before circulating thru the heater core thus providing heat. Without the thermastat, the radiator will do its job well and the water temperature will remain low. The air (in winter) cools down the water much quicker as it passes thru the radiator. Depending on the extremes of the temperature, you may need to block off the radiator like the big trucks do.
In this case, low tech means low cost with desired results. I wouldn't ever block both radiators though, to high a risk in overheating.
Not true, fluid traveling too fast through the radiator will not transfer enough heat, your not looking at air speed through the radiator, your looking at water speed through the radiator. I can wave my hand over a flame, does this mean the flame is not hot enough to burn my hand? is it a myth that fire burns you? no, but the speed of your hand is fast enough that little to no heat is transferred from the flame to your hand, same deal with the water in the radiator. As far as the washer holding "pressure" in the block, that’s not true either, the washer is used as a restrictor to slow fluid speed, the radiator cap is what holds the pressure, bad cap = loss of pressure = boil over.
In a system that does not use a thermostat the water pump impeller has been designed flow at a certain speed, most 2 strokes are by design for one purpose, to be warmed up and ridden at a faster pace. If the designer wanted them to run in the desert at 100+ degrees and get you home in the snow & ice at –20 degrees they would have a thermostat. When you design a system like this you can slow down the pump impeller and create less mechanical drag inside the engine resulting in more “free” power. Most factory superbikes use this set up on the oil pump & water pump (free power), if you let most superbikes idle too long you can hear the rods start to knock, this oil pump in a street bike would kill the engine but in a full on SBK it lives 99% of its life in the 6-15k range where it can generate enough pressure to make due, same with the impeller in the water pump, its designed for a certain fluid speed set fourth by the engineers.
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You are wrong: the pressure cap is there to prevent boiling after the engine is turned off, when the water stopps moving around a cylinder or head hotter than 100 degrees it will boil w/o the pressure kept by the cap. The pressure held by the washer is needed to keep the engine from boiling while running, since it is hotter then.
Water flowing too fast too draw off heat??? That is complete bull****! Faster moving water cooles just as well as, and often better than slow moving water.
All this is explained much better in A. Graham Bells book "two-stroke performance tuning".
Water flowing too fast too draw off heat??? That is complete bull****! Faster moving water cooles just as well as, and often better than slow moving water.
All this is explained much better in A. Graham Bells book "two-stroke performance tuning".
Stolen from www.stewartcomponents.com/techtip3.htm
A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures.
Years ago, cars used low pressure radiator caps with upright-style radiators. At high RPM, the water pump pressure would overcome the radiator cap's rating and force coolant out, resulting in an overheated engine. Many enthusiasts mistakenly believed that these situations were caused because the coolant was flowing through the radiator so quickly, that it did not have time to cool. Using restrictors or slowing water pump speed prevented the coolant from being forced out, and allowed the engine to run cooler. However, cars built in the past thirty years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system. This type of system does not subject the radiator cap to pressure from the water pump, so it benefits from maximizing coolant flow, not restricting it.
A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures.
Years ago, cars used low pressure radiator caps with upright-style radiators. At high RPM, the water pump pressure would overcome the radiator cap's rating and force coolant out, resulting in an overheated engine. Many enthusiasts mistakenly believed that these situations were caused because the coolant was flowing through the radiator so quickly, that it did not have time to cool. Using restrictors or slowing water pump speed prevented the coolant from being forced out, and allowed the engine to run cooler. However, cars built in the past thirty years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system. This type of system does not subject the radiator cap to pressure from the water pump, so it benefits from maximizing coolant flow, not restricting it.
Ok, with all being said please explain the following-
"The pressure cap is there to prevent boiling after the engine is turned off"
Why don't "MOST" MX bikes, snowmobiles, a t v's, road race bikes use a coolant over flow tank and why can I shut off a hot MX or Road race 2 or 4 stroke bike and not have it over flow? If the cap is for pressure relive after the engine is shut off then in theory all the machines listed above should leak coolant after being shut down while hot.
"Water flowing too fast too draw off heat??? That is complete bull****! Faster moving water cools just as well as, and often better than slow moving water. "
Please explain how a faster moving xxx will transfer heat better? If you look at anything - air, water, fire, etc......, it will transfer more temperature at a slower speed, if you move a given amount of xxx across a given amount of space at different speeds it will effect the heat transfer, look at heating & AC, if you have your heater core at say 150 deg & your fan on high the air will be cooler than if your fan is on low, why? Because the air going through the heater core is moving faster with the fan on high and can't transfer heat as good. Move you hand over a propane torch slow and then fast and tell me which hand speed transfers heat more effectively?
"However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures"
Thus the reason for a "tuned speed" for coolant flow, too fast not good enough, too slow not good enough. Back to my original post - Most 2 strokes are purpose built and the coolant speed has been engineered into the system via the size of the radiators, speed of the coolant & cap pressure rating.
"The pressure cap is there to prevent boiling after the engine is turned off"
Why don't "MOST" MX bikes, snowmobiles, a t v's, road race bikes use a coolant over flow tank and why can I shut off a hot MX or Road race 2 or 4 stroke bike and not have it over flow? If the cap is for pressure relive after the engine is shut off then in theory all the machines listed above should leak coolant after being shut down while hot.
"Water flowing too fast too draw off heat??? That is complete bull****! Faster moving water cools just as well as, and often better than slow moving water. "
Please explain how a faster moving xxx will transfer heat better? If you look at anything - air, water, fire, etc......, it will transfer more temperature at a slower speed, if you move a given amount of xxx across a given amount of space at different speeds it will effect the heat transfer, look at heating & AC, if you have your heater core at say 150 deg & your fan on high the air will be cooler than if your fan is on low, why? Because the air going through the heater core is moving faster with the fan on high and can't transfer heat as good. Move you hand over a propane torch slow and then fast and tell me which hand speed transfers heat more effectively?
"However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures"
Thus the reason for a "tuned speed" for coolant flow, too fast not good enough, too slow not good enough. Back to my original post - Most 2 strokes are purpose built and the coolant speed has been engineered into the system via the size of the radiators, speed of the coolant & cap pressure rating.
The cap is a relief valve set to limit max pressure at ALL times.
"In a cooling system, a higher pressure equates to a higher boiling point for the coolant. Higher coolant pressures also transfer heat from the cylinder heads more efficiently."
" Higher coolant flow will ALWAYS result in higher heat transfer."
Remember that the object of the game is to cool a lump of hot metal, not see how hot you can make the coolant.
Use of pump speed alone is a poor way to control engine temperature. It has only one input, RPM. It's blind to important data points like engine load, coolant temp and ambient temp. This is just the condition tx246 outlined in his original post. Compromise like this is the work of accountants, not enginers!
Tinkering with pump RPM or impeller configuration in a streetbike-turned- racebike is likely an attempt to fight pump cavitation, not get free hp.
"If people suffering from heat exhaustion were revived in the same manner most people cool engines, they would be placed in a cold shower set at a trickle. Then the temperature of the water going down the drain would be monitored."
All the stuff in quotes was shamelessly stolen from the Stewart Components website: www.stewartcomponents.com/tech_info.htm
Go there, read and think.
If you have had the patience to get this far on this thread, a little more time spent reading FACTS can only help eliminate MYTHS.
"In a cooling system, a higher pressure equates to a higher boiling point for the coolant. Higher coolant pressures also transfer heat from the cylinder heads more efficiently."
" Higher coolant flow will ALWAYS result in higher heat transfer."
Remember that the object of the game is to cool a lump of hot metal, not see how hot you can make the coolant.
Use of pump speed alone is a poor way to control engine temperature. It has only one input, RPM. It's blind to important data points like engine load, coolant temp and ambient temp. This is just the condition tx246 outlined in his original post. Compromise like this is the work of accountants, not enginers!
Tinkering with pump RPM or impeller configuration in a streetbike-turned- racebike is likely an attempt to fight pump cavitation, not get free hp.
"If people suffering from heat exhaustion were revived in the same manner most people cool engines, they would be placed in a cold shower set at a trickle. Then the temperature of the water going down the drain would be monitored."
All the stuff in quotes was shamelessly stolen from the Stewart Components website: www.stewartcomponents.com/tech_info.htm
Go there, read and think.
If you have had the patience to get this far on this thread, a little more time spent reading FACTS can only help eliminate MYTHS.
Seems we are both right, just looking at it from different sides.
"Remember that the object of the game is to cool a lump of hot metal, not see how hot you can make the coolant."
Your looking at cooling a hot engine and I'm looking at cooling hot coolant, I now see what you guys were talking about when saying that a faster moving fluid cools better - fluid cooling the head & cylinder, not coolant being cooled by the radiator. Something more to add is this, due to the difference in fluid volume the fluid will move faster inside the engine than through the radiator, so it is possible to make both sides happy by moving the coolant slow in the radiator and fast inside the engine. The whole time I thought you guys were saying that moving the coolant faster inside the radiator would cool it better.
"Remember that the object of the game is to cool a lump of hot metal, not see how hot you can make the coolant."
Your looking at cooling a hot engine and I'm looking at cooling hot coolant, I now see what you guys were talking about when saying that a faster moving fluid cools better - fluid cooling the head & cylinder, not coolant being cooled by the radiator. Something more to add is this, due to the difference in fluid volume the fluid will move faster inside the engine than through the radiator, so it is possible to make both sides happy by moving the coolant slow in the radiator and fast inside the engine. The whole time I thought you guys were saying that moving the coolant faster inside the radiator would cool it better.
It's really amazing how two (or more) intelligent people (based on their other posts here) can disagree on stuff. I love it! Heat transfer is a very complex issue, so it's not surprising to see many opinions and mis-conceptions. I'm no expert but I will say that the change in temperature (fingers or coolant) is only a part of the equation.
I have to believe that a bike, without a thermostat, operating in 90 degree air will have a different operating temperature than the same bike in 40 degree air. My questions are: 1) What effect will there be in performance, if any? 2)Would a thermostat correct any difference?
Also, I read the info at Stewart components and they say that plain water (with a rust inhibitor) is the best coolant-they tested all of the additives- no improvement. I thought the consensus here was that Water Wetter, etc. helped?
I have to believe that a bike, without a thermostat, operating in 90 degree air will have a different operating temperature than the same bike in 40 degree air. My questions are: 1) What effect will there be in performance, if any? 2)Would a thermostat correct any difference?
Also, I read the info at Stewart components and they say that plain water (with a rust inhibitor) is the best coolant-they tested all of the additives- no improvement. I thought the consensus here was that Water Wetter, etc. helped?
It was my understanding that water wetter compensated for the slight loss of cooling effiencency that was lost when adding antifreeze. I do know that in the summer when the temp is 100+ my CR500 would boil over when riding tight trails. I started adding water wetter to the mix and it stopped boiling over. Not sure why but it worked.
- Jun 15, 2001
- 2,552
- 0
Ouch, all that & the answer is elementary (to the original question, that is).
Before you'd R&D a product for a vehicle, wouldn't you want to make sure most, if not all, the vehicles would need that product? Now, try to imagine bean counters at Honda thinking about the "breadth of application" of a thermostat on a dirtbike.:think
How many bike builders think the majority of their bikes are going to run flat out in 5th gear across a wide open snowy & frozen plain at 30 degrees F?
I guess KTM does.:)
On a side note, in the auto industry, a thermostat's PRIMARY function is not to make the motor run better, or allow "cleaner" emissions. They were originally designed to optimize warm-up characteristics & get the motor up to 180 ASAP, & then leave it there for purposes of reducing wear . Furthermore, in this day & age, with everything FI, one wouldn't need a Thermostat to assist in proper fuel atomization since the temp would directly translate into a change in MAP & therefore followed by appropriate fuel curve adjustments.
I wonder if any of the Thumpers have thermostats, since valves/guides/seats are particularly sensitive to extremes in temperature.
Guys & gals?:think
Before you'd R&D a product for a vehicle, wouldn't you want to make sure most, if not all, the vehicles would need that product? Now, try to imagine bean counters at Honda thinking about the "breadth of application" of a thermostat on a dirtbike.:think
How many bike builders think the majority of their bikes are going to run flat out in 5th gear across a wide open snowy & frozen plain at 30 degrees F?
I guess KTM does.:)
On a side note, in the auto industry, a thermostat's PRIMARY function is not to make the motor run better, or allow "cleaner" emissions. They were originally designed to optimize warm-up characteristics & get the motor up to 180 ASAP, & then leave it there for purposes of reducing wear . Furthermore, in this day & age, with everything FI, one wouldn't need a Thermostat to assist in proper fuel atomization since the temp would directly translate into a change in MAP & therefore followed by appropriate fuel curve adjustments.
I wonder if any of the Thumpers have thermostats, since valves/guides/seats are particularly sensitive to extremes in temperature.
Guys & gals?:think
SAGE
HOPE THIS ANSWERS YOU QUESTION:
the reason the hand through the flame works is because to the relative transfer times. your hand is in the cool air longer than the hot air therfore radiates the picked up heat. Yor are correct however in the fact that faster moving h20 will not gain as much heat from the engine, but you are not looking at the leat loss side. the same fast moving h20 will not loose as much heat as it passes through the radiators. it you do the math (delta t equation) the velocity is not a factor, as long as the gain/loss transfer areas remain constant, because the time spent in each area will cancel each other out. the air speed however plays a major role. the faster the heated air around the radiator fin is replaced with cooler air, the more efficently the h20 will transfer heat the the air. this is why the idling superbike overheats. Thermostats work by reducing the heat loss area ( radiators).
perssure-
faster moving h20 has less pressure. it is the same with fluids as air. a plane flys because the air moves faster over the top of the wing than the bottom. this creates a low pressure area above the wing, in effect sucking the plane upwards. pump pressure is controiled by dynamic head and flow rate. constricting h20 does not increase pressure past the restriction ( the h20 moves faster but with less pressure and lower flow rate ( they are inversely proportional). the water is actually slowed on the pre restriction side, decreasing flow rate, and increasing pressure. the pressurised h20 works better because the pressure raises the vapor pressure of the h20, raising its boiling point. liquid h20 transfers heat more efficently in the system design, that's why restrictors are used. this is also why when you release the pressuer ( by removing the cap for example, the h20 boils, expands, and comes spurting out of the overflow, cap etc.
everybody follow?
sage- the examples you give work on an open system, but colloin systems are closed, so you have to cons
forgive the tyop's, this thing was too darn long to edit.
if you want me to go more in depth on anything let me know
HOPE THIS ANSWERS YOU QUESTION:
the reason the hand through the flame works is because to the relative transfer times. your hand is in the cool air longer than the hot air therfore radiates the picked up heat. Yor are correct however in the fact that faster moving h20 will not gain as much heat from the engine, but you are not looking at the leat loss side. the same fast moving h20 will not loose as much heat as it passes through the radiators. it you do the math (delta t equation) the velocity is not a factor, as long as the gain/loss transfer areas remain constant, because the time spent in each area will cancel each other out. the air speed however plays a major role. the faster the heated air around the radiator fin is replaced with cooler air, the more efficently the h20 will transfer heat the the air. this is why the idling superbike overheats. Thermostats work by reducing the heat loss area ( radiators).
perssure-
faster moving h20 has less pressure. it is the same with fluids as air. a plane flys because the air moves faster over the top of the wing than the bottom. this creates a low pressure area above the wing, in effect sucking the plane upwards. pump pressure is controiled by dynamic head and flow rate. constricting h20 does not increase pressure past the restriction ( the h20 moves faster but with less pressure and lower flow rate ( they are inversely proportional). the water is actually slowed on the pre restriction side, decreasing flow rate, and increasing pressure. the pressurised h20 works better because the pressure raises the vapor pressure of the h20, raising its boiling point. liquid h20 transfers heat more efficently in the system design, that's why restrictors are used. this is also why when you release the pressuer ( by removing the cap for example, the h20 boils, expands, and comes spurting out of the overflow, cap etc.
everybody follow?
sage- the examples you give work on an open system, but colloin systems are closed, so you have to cons
forgive the tyop's, this thing was too darn long to edit.
if you want me to go more in depth on anything let me know
