I have read a few posts recently about the shutdown practice everyone uses and their seem to be some difference in opinion as to what the practice should be. I too was a proponent of letting the engine idle for a bit after coming to a stop but after owning the winder for a few years I changed my mind.
The history here is that the original turbo designs for gas powered vehicles used bushings, not bearings and there was no consideration for cooling system design changes to accommodate the turbo. The practice became, leave the engine running (idle) for anywhere from a few seconds to minutes to let the turbo properly cool. This works because most engines will cool down when running in an idle state. Modern turbo engines use bearings, not bushings, the impellers are lighter, made from exotic materials, and tend to cool faster, and the overall engine designs are geared to take care of the turbo by adding some form of post shutdown circulation. In many cars this is an auxiliary pump that circulates cooling fluids that continues to run after you shut the engine off.
The 998t in the winder is thermally limited, meaning that it lacks the cooling capacity to keep the engine in its operating temp range, at idle. It relies on the movement of air over the motor, exhaust, turbo, etc and through the radiator to keep the engine cool. The irony of this is that as you are moving, especially if you are accelerating, you are generating more heat but not at the same rate for which you are generating an increase in cooling. If you were to graph this out focused on heat production vs cooling capacity, it would look like a smile, where maximum heat exists at both ends of the spectrum - idle and WFO and somewhere in the middle is the low point or maximum cooling. The attempts to fix this with increased radiator sizes, adding fans and vents, only extend the amount of idle or WFO time but do not cure the problem completely. When you shut any engine down, temps will spike because you are no longer circulating any fluids, so Yamaha came up with a fix.
The fix from Yamaha was the phase change (heat siphon) cooling system or technically a heat pipe thermosiphon. (the gurgle you hear a few seconds after you shut down). The thermosiphon action happens as the liquid (water in your coolant/water mixture) changes state from a liquid to a gas. The expansion of the liquid as it heats makes it less dense until it reaches the point of changing phase into a gas, it then condenses back to water on the other side of that little tank and 'falls' back into the cooling system. This heating, rising, expanding, evaporating, cooling, becoming more dense, sinking, creates the siphon effect and circulates the water. All of this happens as soon as you stop creating little explosions in your motor. The residual heat from the block starts this effect and happens coincidentally with the post shutdown temperature spike and continues as long as the residual heat from the system remains.
Going back to the chart of heat production vs cooling capacity, if you leave the engine running after coming to a stop, you immediately start building temperature. This makes it harder to cool and takes longer to cool the system down. The practice should be (what I have been doing) to run around for a bit using as little throttle as possible, you want maximum airflow, minimum combustion, take it easy before shutting down but once you do stop, shut down. The cooling system is relying on the heat spike to keep the coolant moving. Oil is draining away immediately and ambient under the hood starts to fall immediately post shutdown, all while the thermosiphon is doing its thing.
The history here is that the original turbo designs for gas powered vehicles used bushings, not bearings and there was no consideration for cooling system design changes to accommodate the turbo. The practice became, leave the engine running (idle) for anywhere from a few seconds to minutes to let the turbo properly cool. This works because most engines will cool down when running in an idle state. Modern turbo engines use bearings, not bushings, the impellers are lighter, made from exotic materials, and tend to cool faster, and the overall engine designs are geared to take care of the turbo by adding some form of post shutdown circulation. In many cars this is an auxiliary pump that circulates cooling fluids that continues to run after you shut the engine off.
The 998t in the winder is thermally limited, meaning that it lacks the cooling capacity to keep the engine in its operating temp range, at idle. It relies on the movement of air over the motor, exhaust, turbo, etc and through the radiator to keep the engine cool. The irony of this is that as you are moving, especially if you are accelerating, you are generating more heat but not at the same rate for which you are generating an increase in cooling. If you were to graph this out focused on heat production vs cooling capacity, it would look like a smile, where maximum heat exists at both ends of the spectrum - idle and WFO and somewhere in the middle is the low point or maximum cooling. The attempts to fix this with increased radiator sizes, adding fans and vents, only extend the amount of idle or WFO time but do not cure the problem completely. When you shut any engine down, temps will spike because you are no longer circulating any fluids, so Yamaha came up with a fix.
The fix from Yamaha was the phase change (heat siphon) cooling system or technically a heat pipe thermosiphon. (the gurgle you hear a few seconds after you shut down). The thermosiphon action happens as the liquid (water in your coolant/water mixture) changes state from a liquid to a gas. The expansion of the liquid as it heats makes it less dense until it reaches the point of changing phase into a gas, it then condenses back to water on the other side of that little tank and 'falls' back into the cooling system. This heating, rising, expanding, evaporating, cooling, becoming more dense, sinking, creates the siphon effect and circulates the water. All of this happens as soon as you stop creating little explosions in your motor. The residual heat from the block starts this effect and happens coincidentally with the post shutdown temperature spike and continues as long as the residual heat from the system remains.
Going back to the chart of heat production vs cooling capacity, if you leave the engine running after coming to a stop, you immediately start building temperature. This makes it harder to cool and takes longer to cool the system down. The practice should be (what I have been doing) to run around for a bit using as little throttle as possible, you want maximum airflow, minimum combustion, take it easy before shutting down but once you do stop, shut down. The cooling system is relying on the heat spike to keep the coolant moving. Oil is draining away immediately and ambient under the hood starts to fall immediately post shutdown, all while the thermosiphon is doing its thing.
I think the general idea is that while the engine may build heat at and idle it is much less heat than the Turbo made under stress. Hence the turbo will continue to cool while the engine may continue to heat up after idling. This is evident while running high speed runs across a lake or long field... come to a stop and you can hear the coolant boil. Let the motor continue to circulate until this state ceases.
I thought that as well, what changed my mind was the fact that the sled will overheat at idle. If the motor circulating fluids was effective, the engine wouldn't overheat at idle. The heat under the hood is a byproduct of heat from the exhaust/turbo and no air moving through the rad. Standing still, at idle, the hot exhaust gasses (way hotter than anything else) flowing through the turbo are slowing the cooling process of the turbo coupled to the lack of airflow means you are not really cooling effectively. Yes, the turbo is cooling relative to the temp it was at during a hard pull but most of the temperature change comes from not being actively heated by higher than normal EGT. As soon as you get out of the throttle the exhaust (and turbo) starts to cool dramatically.
The fact that the engine at idle starts heating back up means you are raising the temperature of the fluids you are circulating as well, and to me, that means its not going to cool as fast as if you continue to drive around slowly (think cool down lap), with air moving over the engine and through the rad, the coolant (and turbo) will come down to normal operating temperatures much faster, then stop and shut down without idling.
Doc Harley
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When I do any kind of 1/8+ wot, I like to keep it moving for a bit B4 I stop. I don't sit at idle for any length of time. Just me
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Ditto. I drive around in good snow slowly. Get good snow up on heat exchangers, turbo will cool dramatically cuz exhaust temps go way down (compared to hard pull).
Well i think the Sidewinder is very inefficient at cooling because there is no fan/radiator. Of course the turbo is making a ton of heat, but the only thing that will cool it is the the coolant running through the motor which relies on the heat exchanger.
Ultimately even though the motor is running up in temp it's lower than the temperature in the turbo allowing it to cool before the oil running through the turbo burning and coking, destroying bearings in the turbo.
Have many turbos died in winders? I have seen a few fail but it wasn't because of coking in the turbo.
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A turkey will still cook inside when removed from the oven.
Turbo same thing.
Let it cool down some.
Turbo same thing.
Let it cool down some.
I guess to directly answer your question is it better to idle or as you put it drive around slowly to cool the turbo i'm not sure that is a practical option for those who have to stop at the next intersection waiting for there riding buddies to catch up to the group. this is the most common scenario for most riders unless riding solo. the options are stop shut down, or stop idle. maybe slow cruise would be best for cooling but the group would be left behind at an intersection.
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I had to think about this one in a more practical sense. I guess the proper answer would be unless you're riding hard enough to throw snow on the cooler your relying solely on air cooling on the heat exchanger.
This is how I've always done it:
When I get home from a ride, and engine temp is lets say 170 degrees. I pull sled in garage, and let it rest for a minute while I take off helmet, jacket etc.
After a minute of rest, I start sled again, temp will be over 200. (It rises once stopped in garage or what is measured in the head rises.). I let sled idle for approximately 15 seconds, while watching temp gage go from 200 down to 160s. Then I shut it for good.
If stopping after a long/hard pull, the engine/turbo will really get heat soaked. I'll perform the exercise above 2-3 times until temps are reasonable. This has been a habit, as I hate the gurgling sound. May be normal, but sounds like it's boiling over, and my OCD can't have that.
Years ago it was discussed that this pooling of hot antifreeze in motor is hard on the water/pump impellor and may shorten its life? I don't know......
When I get home from a ride, and engine temp is lets say 170 degrees. I pull sled in garage, and let it rest for a minute while I take off helmet, jacket etc.
After a minute of rest, I start sled again, temp will be over 200. (It rises once stopped in garage or what is measured in the head rises.). I let sled idle for approximately 15 seconds, while watching temp gage go from 200 down to 160s. Then I shut it for good.
If stopping after a long/hard pull, the engine/turbo will really get heat soaked. I'll perform the exercise above 2-3 times until temps are reasonable. This has been a habit, as I hate the gurgling sound. May be normal, but sounds like it's boiling over, and my OCD can't have that.
Years ago it was discussed that this pooling of hot antifreeze in motor is hard on the water/pump impellor and may shorten its life? I don't know......
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270hp here. What I've always done is ride slow/easy the last minute. This cools it to operating temp, and when I stop, I let it idle until the rpm climbs down, wait 5-8 sec then shut down. I know the temp rises a lot after parking, so I'm interested in keeping that turbo up to shape.
Since I'm not a fan of assumptions, and like hard evidence I'll do a comparison with/without idling and check if there's any difference on the temp gauge after stopping. If I can get a hand on one, I'll use a heat camera/laser and measure directly on the turbo. It is a good idea to start it up again and watch it cool down, so I'll try that too.
Anyone know what Yamaha says about this?
Since I'm not a fan of assumptions, and like hard evidence I'll do a comparison with/without idling and check if there's any difference on the temp gauge after stopping. If I can get a hand on one, I'll use a heat camera/laser and measure directly on the turbo. It is a good idea to start it up again and watch it cool down, so I'll try that too.
Anyone know what Yamaha says about this?
Found this in the brochure that came with my sled.
"Liquid Cooled Turbo Body
When the engine shuts down, the convection energy produced by the
super-heated coolant at the turbo head keeps circulating without the
coolant pump in operation which eliminates the need for an engine cool
down cycle, all while maintaining the turbo components' durability."
