Polaris Engine and surrounding information

I am going to bow out here Kelsey....just not worth where this is going...I don't stand to make a dime from anyone for any part on a pro motor. You have your opinion on what causes the motor issues, I have mine..lets just leave it at that and let joe average consumer decide which one makes sense to him.. Good luck, Mike

129 degrees

Myth or fact: Pro ECU will start de-tuning engine when water temp goes above 129 degrees ?

Myth or fact: People running RKT head have noticed water temps in the mid 130's?

I ran a drop-in kit last year and experienced 138-142 in deep snow conditions. I think it might have to do with the temp sensor being placed closer to the PTO dome in the cylinder head. Might be picking up hotter water than it does in the stock head where it's located closer to the Tstat. Not bashing the kit, as I just re-installed it in my 12 assault tonite:face-icon-small-win, Just trying to figure out the best temp to run the engine at and why I have seen higher temps with this head.

roni87 said:

Myth or fact: Pro ECU will start de-tuning engine when water temp goes above 129 degrees ?

Myth or fact: People running RKT head have noticed water temps in the mid 130's?

I ran a drop-in kit last year and experienced 138-142 in deep snow conditions. I think it might have to do with the temp sensor being placed closer to the PTO dome in the cylinder head. Might be picking up hotter water than it does in the stock head where it's located closer to the Tstat. Not bashing the kit, as I just re-installed it in my 12 assault tonite:face-icon-small-win, Just trying to figure out the best temp to run the engine at and why I have seen higher temps with this head.

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The water temp subject was a big topic last season my rkt (cheater) head was running 130-135 on hard pulls, guys were saying we were loosing power at 129 so I did the doo stat and my temps are now 109-116 on hard pulls and I saw no change in power so I would say its a myth (I also put in resistors to tell the computer it was cooler, no change in power )

ok rkt...i get what your saying

but...if the motor is cooling down...the water is fully saturated and pulled as much heat out of the motor is it could have...annnndd...the effect of colder water cools the engine even more...when the colder water is added...with the effect of the engine running...not so much a cold shot because that would be a poor choice of words...but more like a cold sieze?

RKT said:

Well. we never see that high of water temp.. we had a plugged line last season and at 160 the sled would barely run...(on purpose.. by Polaris design) you must have a 2011??

Also, you can be sure that your engine temp is always over 180 degrees.. this coolant temp is no indication of what your engine temp is... this is part of the misconception.....

How to you think your coolant reached 180 with the engine off??

YUP... the engine heated it... You can't heat another object to 180 unless you are AT LEAST 180....so, having 180 degree coolant temp for the short time the sensor reads it after start up, is not going to upset the engine since the heat came from it.. The engine is actually cooling down.. not heating up...

Then once started.. the engine gets hotter and hotter all over again.. No stress on the engine when the coolant temps are hot since it is always hotter and the hot coolant temps only last a VERY short time...

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100% Agree! Heat will always travel from hottest to coolest point until all temps are equal. Eg gas compressor cylinder temps 325c, coolant leaving cylinder 75c. Engine shuts down, after a couple min at jacket water temp rises to 90c. High temp shut down rings in. Jacket water continues to warm to 120c. Cylinder temp still at 280c so jacket water temp will continue to rise. Unit starts up, trends back to normal with no big swing in cylinder temp. And a 2500hp 2 stroke v8 gas compressor has much larger jacket water coolers that hold much larger volumes. And I can trend every temp every second during start up or shut down. Bit of a odd comparison but the same idea. :beer;

I wonder the possibility of installing some sort of inline water pump.
Then you could keep the water flowing during short shut down times.
This way, the engine would be cooling faster, but also all components would be equal temps.
No cold water in the coolers to hit the motor.
Would have to be on elec. start sled, or install a battery to run it .

Now, once the heat has reached your fingers and you set down the metal piece.. and remove the lighter (heat source)... Set it on the floor.. Wait 30 seconds and try and pick it up again.. What happens?? It is even hotter than it was before... WHY? Because the heat is still transferring to the colder (where your finger was) area.. If whatyou say was true... the piece would be cooling down not heating up (like it is)... The pieces is trying to obtain temperature equilibrium... Just like your engine... Try it you will see....

Your engine can NOT be cold shocked when running... It simply can not happen... The heat that is being produced by your running engine is FAR more powerful than your coolant that is passing by in the water channels..

This is where the misconception lies... You can not cool the heat SOURCE (engine) you can only cool the components that surround the heat source like the cylinder, head, etc...

Actually you can cold shock a motor while running, most everybody has been dirt biking and then splashed thru a creek. Think about how your bike runs coming out the other side. That is due to cold water hitting a hot motor and contracting around a heat soaked piston. Same thing happens on a sled. I believe someone posted that after sitting for 10 Min with a pro it does not run right when they restart. This is due to the cold coolant hitting a hot Motor and contracting around a heat soaked and expanded piston. We HAVE put cylinders in the oven and measured then put them in the deep freeze and measured. Try it. It will amaze you how much change the cylinder goes thru. If you study Metallurgy you will find that Metal Contracts and expands with every degree of temperature change. Up or down. For example. If you need to remove or install a pressed on bearing you heat it up to expand it then install the bearing. Now let that bearing cool and you will not get it off. Tight bolt? Heat it up and take it off. I don't think anybody can argue with me on that.

temp difference

the disagreement I have with the "cold shot theory" is the fact that when you do refire after sitting, you are not shocking the engine with ICE COLD COOLANT. On the large end of the spectrum I see the temps change on refire from 145f/150f on my 11,12,13, down to 100f after start up then almost immediately back to 118f and holding. This is not a massive swing in temp. This small variation in temp absolutely can not create "core shift". The monos with cracked cylinder skirts that I have changed (before failure) all show the same "j" shaped crack dead center of the boost port. If material shift is the problem here then why do I not see cracks in different places on the skirt. If temp change on refire is a contributing factor then why do I see cracks on alternating skirts and not the same skirt that comes into contact with the changing temp first. In all the units that I have installed aftermarket pistons in, mono shim or not, the return failure rate has been 0 for cracked skirts. The only units I have had come back are the lower connection rod bearing failure and I believe has to do with reciprocating mass. Now I will choose the light component every time. I work on Polaris all day every day so this is not info pulled from my backside.

Outlaw said:

Now, once the heat has reached your fingers and you set down the metal piece.. and remove the lighter (heat source)... Set it on the floor.. Wait 30 seconds and try and pick it up again.. What happens?? It is even hotter than it was before... WHY? Because the heat is still transferring to the colder (where your finger was) area.. If whatyou say was true... the piece would be cooling down not heating up (like it is)... The pieces is trying to obtain temperature equilibrium... Just like your engine... Try it you will see....

Your engine can NOT be cold shocked when running... It simply can not happen... The heat that is being produced by your running engine is FAR more powerful than your coolant that is passing by in the water channels..

This is where the misconception lies... You can not cool the heat SOURCE (engine) you can only cool the components that surround the heat source like the cylinder, head, etc...

Actually you can cold shock a motor while running, most everybody has been dirt biking and then splashed thru a creek. Think about how your bike runs coming out the other side. That is due to cold water hitting a hot motor and contracting around a heat soaked piston. Same thing happens on a sled. I believe someone posted that after sitting for 10 Min with a pro it does not run right when they restart. This is due to the cold coolant hitting a hot Motor and contracting around a heat soaked and expanded piston. We HAVE put cylinders in the oven and measured then put them in the deep freeze and measured. Try it. It will amaze you how much change the cylinder goes thru. If you study Metallurgy you will find that Metal Contracts and expands with every degree of temperature change. Up or down. For example. If you need to remove or install a pressed on bearing you heat it up to expand it then install the bearing. Now let that bearingcool and you will not get it off. Tight bolt? Heat it up and take it off. I don't think anybody can argue with me on that.

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I can see really cold water hitting a hot engine driving threw a creek causing a cold shock or filling an engine block that's out of water and glowing hot out of a garden hose causing a cold shock, but I don't see it as a cold shock when you start your sled after setting for 5 mins and the temp is 160 and 80 degree water comes in and directly hits the temp sensor first then mixing with the warmer water as it travels threw the engine its not really the same thing as shocking the hot engine with ice cold water or filling an overheated engine with cold water that's got no water in it. Imagine taking a pan putting it on the stove heating it up to 180 degrees then dump cold water in it ok yes that's a cold shock or a massive temp change that will cause metal to twist and bend ( expand and contract) then do the same thing with a pan full of water bring it to 180 degrees and pour in some warm water the warm water may change the temp a little but will equalize fairly quick, so think about your engine agin it's not getting 80 degree water instantly threw out your top end it takes some time and it also is mixing with the 180 degree water and equalizing the temp, also keep in mind the temp sensor is right next to the thermostat so it sees the cool water first that's why it drops on the gauge but our entire engine does not see it that fast. Hope this makes sense

I have to ask, are people here saying that it is okay to just ignore warm up and stabilizing engine temps after a short shutdown on a liquid cooled motor in winter conditions?
If you are, shame on you for giving bad advise to the readers.

Engines clearances are stable and correct at operating temps. That is designed in for proper engine management (EPA) and engine life (warranty). Comparing a 1000 lb motor to a 100 lb motor is just silly unless you are trying to mislead or do not understand the difference in expansion between a thin piece of aluminum and a thick piece of cast iron.

Cold seizure is a fact not a myth. It's been around since the first aluminum pistoned two stroke. You even see it on the new light weight, slipper piston, forged block 4 strokes of today. If there was not a need to control engine expansion rates a lot of big manufacturers have wasted a lot of time and money designing in dual thermostat systems to work with their newer light weight engine needing to work at EPA lean engine management temps.

The heat if created in the head from combustion (as pointed out). The heat is transferred in to the piston crown then down the piston with some being lost through ring contact but that is not much until the piston has stabilized in size and ring land contact is to size. If you want to now how much the manufacturer expects for expansion measure the difference between the skirt and crown on a cold piston. It is huge because of material used and temps needed to be absorbed. Higher compression makes this initial expansion happen quicker (more heat created).
The all aluminum cylinder needs the coolant at a certain temp to be stable clearance wise. Add coolant that is at a cooler temp and the heat goes into the coolant out of the aluminum and the cylinder reduces in size.
This is fact not myth.

A piston at operating temp and a cylinder too cold equals too tight a clearance, equals the term and possibility of cold seizure or maybe the term "cold shot". Don't be mislead it is very important to properly warm up a motor (especially in the winter) and be very aware of the need to allow that to happen again after a shut down (but it doesn't take as long).
To compare the CFI motor to a modern Suzuki laydown motor with reverse flow cooling is wrong and as pointed out the older Suzukis were closer to the same. Guess what, the 580's, 600's, 700's and 900's suffered from piston life and failure issues if not properly warmed up too.
Doo must of wasted a lot of money (if waiting for the engine temps to stabilize is not important) adding liquid cooling to the crankcase and a engine management system that reduces power until the temps stabilize. Doo riders, whether you know it or not, Doo is controlling your thumb on the ETEC until they feel the engine is warm enough. That`s a good thing to do.

Cold pipe causing poor running after a short stop. Nahh, I don`t buy that theory. The exhaust temp sensor takes care of that. If you want to prove it to yourself , unplug your pipe sensor and take it for a ride when cold. Get ready for a bog or two lol.
My theory is the difference in the IAT sensor temp and actual IAT is the cause of that. It goes away quite quickly though. Far less time than it take to warm up the pipe completely.
Unless you are looking for max power and powerband immediately upon start up the dimentional stability of the pipe has little effect. Even hot most pipes still make more half way into a short pull. The guy who dropped into a creek with his bike definitely had a cold pipe AND cold crankcase issues but, did that pipe have an exhaust temp sensor to compensate? Maybe a little water sucked in too?

Going back to the original 4 points (myths lol). Long rod needed? (I think this is maybe finger pointing too but could be wrong).
1; CMX is long rodding their builds. Why? Probably powerband is MO. I hope to do that this season (if work would slow down lol)
2; Cold shot. Ya, it is a fact of life in ANY motor. Smaller (less mass) with more power equals larger and quicker swings in dimensional changes. So be aware of it with the Pro.
3; Don't know but mine is good lol.
4; Don't know but none of the measuring methods I saw last year proved or disproved it to me. You would need to be able to draw a line through the crank center to piston crown center and see if the center of the big end pin on the rod is on that line at TDC also. It's been done before.

With the piston issue I would like to hear some facts and see data too. It's been debated (polite eh) many times and yet I still don't know.
My pistons showed acceptable wear and no signs of collapse (excessive clearance). Rings looked ok but ring lands were too loose cold (not the best way to check). I see lots of Pros still running with what I call high mileage for a sled. I've seen lots of ring issues on this site though.

Simple question to anyone out there. What is the main cause of the piston collapse (too much clearance and dimensional change referred to)?
Is it excessive heat causing a material change or failure? Is it blow by created by ring issues (leading back to the first question)? Is it wear beginning at the bottom because the taper is designed wrong (stupid Polaris eh)? Are the pistons too heavy? Is the piston simply too weak in structure in the skirt area?

I would like some data please. I would really really like to know.
\I have nothing to input on that point because mine are still fine (dang it).

Cold shot

Just so everyone is clear, I was only stating my theory on the cold shot question I in no way shape or form meant it by saying it was ok to start a cold or not temp stabilized engine and hammer the throttle and hit the hill full throttle. Yes it a very good idea to get any engine up to operating temp before hammering down.

tinkerjohnson said:

I can see really cold water hitting a hot engine driving threw a creek causing a cold shock or filling an engine block that's out of water and glowing hot out of a garden hose causing a cold shock, but I don't see it as a cold shock when you start your sled after setting for 5 mins and the temp is 160 and 80 degree water comes in and directly hits the temp sensor first then mixing with the warmer water as it travels threw the engine its not really the same thing as shocking the hot engine with ice cold water or filling an overheated engine with cold water that's got no water in it. Imagine taking a pan putting it on the stove heating it up to 180 degrees then dump cold water in it ok yes that's a cold shock or a massive temp change that will cause metal to twist and bend ( expand and contract) then do the same thing with a pan full of water bring it to 180 degrees and pour in some warm water the warm water may change the temp a little but will equalize fairly quick, so think about your engine agin it's not getting 80 degree water instantly threw out your top end it takes some time and it also is mixing with the 180 degree water and equalizing the temp, also keep in mind the temp sensor is right next to the thermostat so it sees the cool water first that's why it drops on the gauge but our entire engine does not see it that fast. Hope this makes sense

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Just so you know it hits the front of the motor first and has to travel thru the motor before it hits the temp sensor and the thermostat. The coolant does not hit the temp sensor first. The cold coolant coming in pushes the hot coolant out to the tunnel coolers. This is why you see the drastic temp swing on the gauge. In testing we saw heat soaks up to 190-200 then down to 80-90. We also saw coolant returning from the tunnel coolers below 50 degrees. Just like your pan. A 100 degree temp swing contracts the cylinder but not heat soaked and expanded pistons.

well not sure if you know this


but an out of tune pipe isnt caused by a pipe temp sensor being wrong

you are actually altering the original vacum and the second return wave because the speed of sound changes with tempature...and exahust flow through a 2 stroke pipe is around the speed of sound...it has the same affect of altering the tuned length of your pipe

this cold shot is getting more and more myth like to me

im not going to be worried about it this winter...but even if there is a cold shot...what happens? is it cylinder cracking...piston seizure...or what? i have warranty on my engine so i will gladly test this cold shot thing this winter

ok...i have a question...does the water enter the top of the cylinders...and then fall down to the front of the water pump...or does it get pushed up from the bottom and reach the top?

RoffRider said:

ok...i have a question...does the water enter the top of the cylinders...and then fall down to the front of the water pump...or does it get pushed up from the bottom and reach the top?

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Flow is bottom to top on the Polaris'; starts at the water pump, exits to the front side of the crankcase, up the front of the cylinder, around the exhaust port, enters the front side of the head, continues across the head to the thermostat, and out.

Hope that helps visualize the flow.

Outlaw said:

Just so you know it hits the front of the motor first and has to travel thru the motor before it hits the temp sensor and the thermostat. The coolant does not hit the temp sensor first. The cold coolant coming in pushes the hot coolant out to the tunnel coolers. This is why you see the drastic temp swing on the gauge. In testing we saw heat soaks up to 190-200 then down to 80-90. We also saw coolant returning from the tunnel coolers below 50 degrees. Just like your pan. A 100 degree temp swing contracts the cylinder but not heat soaked and expanded pistons.

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Ok your right, I was looking at it wrong the water does travel that direction but seems to bring temp back up fairly fast I am running the doo stat now and the temps seem to be a lot more consistant thanks for correcting me

There is no cold shot. if there is, it would take numerous times of repeated exposure to have an effect.

Its not like firing a cold engine and going for broke.

There is some expansion and contraction going on, but the parst are for the most part in relative same temp range.

After exploring the theories, piston fitment is still the root cause.

the next main problem is having a computer control the parameters of an engine built to run in extremes.

This to me is the main issue. Someone mentioned gm vehicle computers earlier.
Sled ECU's aren't nearly as sofisticated as car ECU's.
Couple that with parts made in every corner of the world, and WAALAA. Here's your sign.

With that being said. I have had the injectors replaced, and also the pistons and monoblock due to a crack on the pto intake side cyl skirt.

Never been left trailside. Still the most fun i've had on the snow.

Except that one time...............