why dont 2 strokes use thermostats?

[tx246]

lots of great info!!

but the real question i guess is how would a thermostat be a good thing? i am guessing that jetting would be more consistent and power would be much more consistient over a wide operating range. from everything i have read in books about engines heat is not a bad thing to a degree. thermal effiecint engines ect. i know there are cons as far as thermostats go. ie stuck thermostats. but what are the potential benefits? is worth doing? i know im getting heat in the motor with the old cardboard/radiatior trick but it is hard to know if it is too much.

 

[2fat2riderit]

thermostats on dirt bikes

I've been curiously following this topic for several weeks now, and didn't know which side to agree with. So I just made my own prototype of a slip on thermostat housing which uses a small Stant 192 degree thermostat. I machined the housing from a piece of billet round alluminum stock I had laying around the shop. It has ends just like the other factory outllet nipples and fits between the head water ouitlet and the radiator (this is for my son's 2002 Yamaha YZ85). It fits nice and snugunder the tank. I'm hoping for a faster warm-up (as mentioned earlier) and more consistent running. Trying to get the plug from fouling so fast. Already have gone down one jet size on main and pilot from stock.;)

 

[yardpro]

2fat2riderit

i'm green with envy of your cool cnc toys. :)
let us know how it works.

 

[LJW]

If anyone feels a need to experiment, take a look at the cool LITTLE thermostat assemly on a KAW EX500 streetbike. Has hose barbs on both ends. If the hose diameters are compatible it would be easy. I bet the bike boneyards have plenty of them at a low buck price.

One test is worth a thousand expert opinions, but the opinions are easier to get.

 

[atc3434`]

I think a termostat would be a great thing in a two stroke dirtbike. After riding my KDX220 (which is jetted absolutely perfect for about 75 degrees) in 40 degree temperature, I've come to think that keeping the motor warmer would help a slightly lean low mid condition that has seemed to have developed. This, however, could also be because the air is denser, and is causing the mix to be a little light on the gas. I should just move the needle up a little. But a termostat would be nice too, and would help warmup. An interesting side note, I have two temp gauges in my car, one for engine temp, and another temp gauge which gives me my coolant temp at the radiator. Its amazing how much the radiator temp moves in comparison to the engine temp. You can deffinatly see how the termostat works. Of couse now its winter, and the thing rarely opens up, even on long drives at highway speed.

 

[yz250roost]

back to the basics

I like to ride dirtbikes.....I don't care if they have a thermostat.....as long as I can ride my bike I am happy and if it's not overheating then I'm not going to complain.....let's get back to the basics guys........

 

[demographic]

As my kx 500 is registered for the road but also gets used off road it is subject to vastly differing airflow, this may help.i will have to find out cheers

 

[jmics19067]

wow lot a talk for the original question my guess is that a thermastat on a bike woudl make it easier to jet since the operating temp of the bike would be always close to the same but you would probably still need to rejet for air and fuel temp cold dry air requiring bigger jets than hot humid air but then agian cold dense fuel would recquier smaller jets than hot fuel uuuughhhhhhhh maybe you owuld need less jets to fit extremes? antifreeze is just that you mix it with water at a 50 50 mix to keep it from freezing at -20f plus stuff to lubricate the water pump and prevent corrosion of the insides of the water passages the radiator cap is to keep pressure inside the system which prevents boiling of the water the reason it is a pressurre blow off cap insstead of sealed is so you cant blow the rubber hoses or seals or anything out I have seen vehicles with stuck open thermastats over heat in the summer . so I do not belive that the keeping the water in the radiator longer to keep it cool is a myth . but I dontknow if somebody actually plans thatout turning a water pump powersteering belt alternator slower with differnts shape pulleys does lessen the parasitic horsepower loss and also prevents the accessories from building too much pressure at high speeds. why I am talking about a race car here ? has no bearing on you dirt bike since I doubt highly that you are going to change the imppellor shaft speed on your bike

if you dont like your ktm dealer go to a differnt one I ma sure there are plenty in the country who would be more than happy to ship you one
which ktms comes stock with a thermastat? is it something they believ is performance and comes on all race bikes? is it something for ease of jetting maintenance so the austrian army corp dont have to rejet in the alps I would take a look at what bikes the ktm has the thermastat in and try to imagine what kind of riding the bike was meant for and take a guess if you think it would help your not and see if it worth it to try <cost of part and possible modifications cutting a house inhalf and buying 2 hose clamps?> I have thought about using one myself but never exceeded the demand to add water or rejet for me to acrtually look into it

 

[jmics19067]

Originally posted by atc3434`
I think a termostat would be a great thing in a two stroke dirtbike. After riding my KDX220 (which is jetted absolutely perfect for about 75 degrees) in 40 degree temperature, I've come to think that keeping the motor warmer would help a slightly lean low mid condition that has seemed to have developed. This, however, could also be because the air is denser, and is causing the mix to be a little light on the gas. I should just move the needle up a little. But a termostat would be nice too, and would help warmup. An interesting side note, I have two temp gauges in my car, one for engine temp, and another temp gauge which gives me my coolant temp at the radiator. Its amazing how much the radiator temp moves in comparison to the engine temp. You can deffinatly see how the termostat works. Of couse now its winter, and the thing rarely opens up, even on long drives at highway speed.

most cars would have a sensor for coolant temp in the radiator to tell the electric fan when to start and stop and now thatits winter you would less likey to get hot on a long drive at highway speed because lots of cold air is going thru the rad and engine compartment sit in traffic for a long time and shoudl get hotter quicker

 

[reynome]

After taking thermodynamics I will conclude SAGE is correct. Sorry guys, you are all wet if you believe that taking out the thermostat will allow the engine to run cooler.

Its as simple as delta T, go look at the equations for open or closed loop systems for heat transfer.

BTW break out your diff eq book for solving the closed loop expression for heat transfer of a closed loop system. They all have delta T, no time no heat transfer, its that simple.

 

[Milquetoast]

Originally posted by reynome
After taking thermodynamics I will conclude SAGE is correct. Sorry guys, you are all wet if you believe that taking out the thermostat will allow the engine to run cooler.

Well, after being a mechanic for 12+ years I can tell you that if you take the thermostat out of the engine it will run cooler. Done it a bunch of times, you don't need a book to figure that one out. Try it on your car some time, watch where the temperature gauge normally is with the t-stat and then on a cold day without the t-stat it will read lower.
The thermostat is a restriction whether it is open or not, that is one reason. But a thermostat is primarily there to keep the temperature up in the range where the engine will run most efficiently. (not for the heater to work) So, on a cold day it will open and shut all day long to keep the temperature in the correct range. Take it out and the temperature will drop.

 

[yardpro]

Milquetoast
you're absolutely correct. One of my company trucks was overheating last week. Had H20, no leaks, pupm good, so I pulled the thermostat. teh truck wouldn't heat to over 100 deg. Put the new one in and viola- perfect.
All the book smarts in the world doesn't doo you much good without common sense and common sense is gained through experience.

 

[jmics19067]

I still have seen trucks over heat with a thermastat that was stuck open

 

[WorldWideRacer]

2-strokes with thermostats

Yes, they do make 2-strokes with thermostats. Every street-legal 2-stroke I have seen here in Japan has one, including my NSR.

I am not sure why they do this, but it is probably related to the higher speeds that the street-legal bikes usually run. For instance, my YZ peaks out at maybe 60 mph, but on the track rarely sees that speed and maintains optimum coolant temperature well. The higher speeds of the streetbikes cause the radiators to transfer more heat, which would run the coolant temperature much lower than optimum temperature. The thermostat then intercedes and keeps the engine temp at or near optimum.

I still think that KTM is heading the right direction by putting them on their bikes. I am sure this adds to the overall durability of the bike and probably helps the jetting, as well.

 

[Wanker]

Keep this up and your going to have to explain wind chill factor....

Is that delta t or delta T ???

Oh Professor Mossberg forgive me.....

 

[LJW]

Right On WANKER!
I think my hillbilly analogies caused enough trouble without involving math. I will leave that to braver men. Stuff like this forces you to think. Is it possible that this is what the creators of these forums had in mind?

 

[2nat2]

Slightly off subject

I wonder if the thermostat on KTM's improve durability. KTM's have a reputation for extremely long lasting top ends in their bikes. If the thermostat's are part of that it would be an easy way to increase the life
of top ends.:cool:

 

[DanS]

It was my understanding KTM puts the thermostats on the bikes to help them warmup faster.

 

[DVO]

Seems to me that if you want it to warm up faster, just don't ride it. No air flowing thru the rad=faster warmup.:D
Consistent operating temp at any speed=consistent performance

 

[Sage]

Here we go again.......

It seems that it really comes down to design, I have pulled out t.stats and seen it go both ways, almost every sportbike that I've worked on thats seen the race track on a regular basis will overheat without the t.stat installed except the older ones with the bigger raditiors on them. I've seen it in cars also, my neighbors BMW was overheating, found a t.stat stuck open, it has a smaller raditior. A 78 blazer I had, it also had a stuck t.stat and would never heat up, it has a massive 4 core diesel raditior it was once diesel, switched over to to a gas engine.

if you look at most newer bikes they are super compact with raditiors that hold less than a gallon, ideally you want fast moving water through the engine and slower moving water through the raditiors because the're so small it hard to cool the water(and yes I taking into account that air is moving through the raditiors). As for who ever said on page 1 the superbike I was talking about overheats because its sitting in the pits and no air is going through the raditiors missed what I meant to get across, if you pull that water pump and install it on its street bike counterpart and try to ride in traffic it will overheat, it pumps water slower to eliminate the use of a t.stat and reduce mechanical drag on the engine, it primary air speed through the raditors is usually over 70 mph so you will have good heat transfer, at the same time due to the fact that there is only a cup or two worth of water in the engine and a half gallon in the raditiors the water will move fast in the engine and slow in the raditiors.

Results vary, IMO I feel it all falls into system design, making a open ended statement that removing the t.stat will reduce engine temp is not true, I have done it, hands on, no books, and have no idea what the heck the formula's are.

 

[Onore GT]

Regarding the thermostat on the KTM, I think the reason for adding the thermostat in the beginning was to prevent cold seizures and clean up the jetting on street legal 2 strokes. The in-line thermostat was first added to the street legal models but did not really solve the cold seizure problem. In theory the system should block the circulation of coolant through one of the radiators and then once the coolant is up to the appropriate temp, the thermostat would open and allow the lower temp coolant to mix with the rest of the coolant. What would happen is that the water would not mix properly and allow a rush of cool water into the cylinder head. Now the street legal 2 stroke models have a more involved system that will not allow the cold water to be released into the cylinder head without proper mixing with warm coolant. The in-line thermostat is still on EXC/MXC models to maintain consistent water temp while running but does not necessarily help with warm up like one would think.

 

[Bobt250]

It's intuitively obvious that removing a thermostat would make an engine run cooler. The assumption that faster moving water does not absorb heat presupposes that somehow the water loses contact with the metal surfaces due to it's speed since that fact is that faster moving water is still water and is still in conatct with the metal. And yes.......anyone who's tried it has noticed a cooler running engine without one. Years ago a friend of mine put an aftermarket thermostat on his '85 YZ250. In his case he had only one water outlet on the head whereas my CR250 has two. He barely had room for that one, I could never fit two of them. My assumption is that it's a cost savings as well as space limitations.

BTW, my Mercury outboard motor is a V6 and has a thermostat on top of each bank of cylinders. They are very little things, they might fit on my CR if they had seperate housings but they are cast into the heads.

 

[ktm300]

Do KTM thermostats fail open or fail closed?

I have a 300EXC, if the thermostat fails, will it be open or closed?
Thanks

 

[smokeyhaze]

Yes, or anywhere inbetween.:eek: :scream:

 

[yardpro]

The assumption that faster moving water does not absorb heat presupposes that somehow the water loses contact with the metal surfaces due to it's speed since that fact is that faster moving water is still water and is still in conatct with the metal

\

although I agree that no thermostat= cooler temps. The statement above is not very accurate. The movement of the water moves the heated liquid ( as the entire volume of liquid does not all instantly heat) from the area of heat gain (cylinder) to the area of heat loss (radiators). It the movement was a nonissue then why have pumps atr all?