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Why no thermostat?

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Why does my YZ250 (2005) lack a thermostat? A thermostat seems like a great way to keep a liquid cooled engine at a constant temperature. I can't help but wonder if a more constant engine temperature would make jetting more consistent and easier.

For example I'm strugging to get my son's RM85 to be less spoogy. I've gone lean on every circuit (pilot, main ,needle) and it still seems to spooge some. Now I'm thinking that his engine doesn't get hot enough (no thermostat either). Yes I know tell him to get on the gas, blah, blah, blah; go faster. Still I think a thermostat is a good idea. Do 4 strokes have thermos?

Just a thought.

Peter

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you are not the first to think of this, actually i believe someone is already doing this with a thermostat off a ktm. I know for a fact that the fourstroke KTMs use them, cause i have one.

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To maintain a constant temp as you mention, you would need a t-stat AND a fan AND an battery to run the said fan AND a big stator and flywheel to charge the said battery AND other electrical components..... yadayadayada

You can see where this is going... this would add a lot of weight to a race bike that was intended to do just that; RACE!

These bikes were not made to putt around... they were made to be as fast as possible on the MX track. The ktm's are a different story, many models are designed TO BE TRAILBIKES OUT OF THE CRATE!

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Not to mention that many of those KTM riders report overheating problems and some have even removed the thermostat in an attempt to get better water flow. My son had an 01' KX-85 not sure but I think they were the same bike as the RM back then, I don't remember having any trouble with the jetting on it. If you'd like I could look to see if I still have any info around here on it?

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well you dont need a battery to run a fan just look at a gas gas trials bike no battery their and mine have headlight taillight and horn as well as a fan. i do think a fan on a dirt bike would be a great idea if your like me and only ride single track

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I don't think a fan and battery are necessary for a dirt bike. First, we don't ride in stop and go traffic so there is always airflow over the rads. Second, I'm assuming that the manufacturers have sized the cooling system to be more than large enough. I see the problem of less than increasing the cooling ability under certain conditions but rather to lessen the cooling under certain conditions (low RPM's/load, cold weather, etc). You could do that with just a thermostat. Basically keep the engine hot enough. When the engine is hot enough the t-stat will open fully and you'll have the situation that we currently have right now.

As far as other bikes needing their thermo removed I can only assume that is a design flaw (too restrictive) for the size of the cooling system.

Once again just a though.

Peter

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There were add on thermostat kits sold when bikes first became water cooled. They were really small and would not have added much weight or complexity. Over time, there disappeared and were never seen again.

Based on what I have been able to find they are nt using them for complexity reasons. I have been on rides with my yz where I can promise the engine never gets to proper operating temps. We did a track day last year that had me blocking the left rad and about 1/2 of the right. The temp was way below 30.

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Not to mention that many of those KTM riders report overheating problems and some have even removed the thermostat in an attempt to get better water flow. My son had an 01' KX-85 not sure but I think they were the same bike as the RM back then, I don't remember having any trouble with the jetting on it. If you'd like I could look to see if I still have any info around here on it?

they were not the same bike,

you are probably thinking the rm65 03-05 is the same as the kx65 00-09

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RCannon, what do you think is approx operating temperature? I noticed my coolant temp stays around 145f, I think the max its been is around 165, when i got in some real deep mud and had to hold it wide open for a few seconds.

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I believe 180 engine temp. is considered close to perfect. 145-165 is great for normal conditions.

I wonder who we could ask for a technical answer on the thermostat??? I think part II of the question would be asking if the thermostat on a car is used to help supply warm air from the heater more so than engine performance.

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I believe 180 engine temp. is considered close to perfect. 145-165 is great for normal conditions.

I wonder who we could ask for a technical answer on the thermostat??? I think part II of the question would be asking if the thermostat on a car is used to help supply warm air from the heater more so than engine performance.

And emissions, and engine wear (if the motor never warms up to a reasonable operating temp, wear will increase).

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Don't know if this helps but the KTM thermo's in the parts fiche indicate 2t's = 55*C @ 131*F, 4t's = 70* @ 158*. At what air temperature would a 131* thermo. become effective? Maybe the ice racers can help?

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thermostats on cars are used to keep it in the optimal temperature for the best efficiency. but without a thermostat you do get no heat so i think it serves a lot of uses. i'm pretty sure if you kept a dirt bike at its optimal temperature, with a thermostat or whatever you use, you should get better performance.

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The main function of a car thermostat is actually to help the engine warm up quickly from cold by diverting the water flow, taking the rad. out of the circuit until the coolant reaches the temperature at which the 'stat is designed to open, when it allows flow through the rad too. The reason the heater is less efficient with no 'stat is due to the increased flow leading to the engine running cooler overall (and obviously taking much longer to warm up properly).

Anyway, back onto the subject of why no 'stat on some bikes. Really I'm as confused as the next man as they add next to no weight & could obviously help especially 2-strokes like the YZ by reducing engine wear & likelyhood of cold-seizure. The Cagiva Mito 125 engine (fairly similar to the YZ lump in buildup) actually has a 'stat fitted into the head but many owners of that bike still experience cold running issues, with a lot of the bikes failing to run at more than 50*C on a ride, leading to the blanking of radiators.

This seems like a satisfactory "fix" on these bikes as they have a fairly accurate temp. gauge so the blanking can be fine-tuned or removed as the engine heats up.

I still can't understand why manufacturers like Yam. would not fit a thermostat, unless it was purely to A. Save money on the build and B. make more money for the parts dept. from cold seizures &/or overheats due to attempts to raise temps by blocking the rad.

Strange...

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It is strange. Even though we accuse them of being cheap, they have never been afraid to add things that were "value added."

Look at the ti spring and Kashima coatings. I imagine a ti spring would buy several thermostat assemblies. I looked in Eric Gorrs book and it did mention the thermostat is not used....no idea why.

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a thermostat in a car is to help bring the engine up to operating temps quicker and to hold them their in cold weather. the thermostat brings the temps up and the fan brings them down or air movement through the radiator. the thing i would like to see is both a fan and a thermostat but i only ride single track. i know i love the one on my trials bike.

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Well I'm glad people are as perplexed as I am; I thought I was missing something obvious. Has anyone tired those sticky decals that indicate engine temp? Do they work? Any brand to recommend or how do you measure engine temp?

Not that I'm about to try this but I seems to me that you could create some t-stat fitting and splice it into one of the rad hoses. Out of curiosity (other than KTMs) does any other 2 stroke have a t-stat?

Lastly as far as to why the YZ's are this way does anyone have a contact at Motocross Action? They seem to like these kinds of questions.

Peter

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Well I'm glad people are as perplexed as I am; I thought I was missing something obvious. Has anyone tired those sticky decals that indicate engine temp? Do they work? Any brand to recommend or how do you measure engine temp?

Not that I'm about to try this but I seems to me that you could create some t-stat fitting and splice it into one of the rad hoses. Out of curiosity (other than KTMs) does any other 2 stroke have a t-stat?

Lastly as far as to why the YZ's are this way does anyone have a contact at Motocross Action? They seem to like these kinds of questions.

Peter

Peter, I have two of the sticky decals that are supposed to tell the temps. One on the left radiator and one on the cylinder. They are both of the low temp variety. The range is from 149-248 degrees f. I have seen the one on the cylinder light up the 149 degree block once..never the radiator. For all the good they did me I might as well shoved them up my...well, nevermind.

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