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Who Warms Up Their Engine Anyway?

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Paul Olesen

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Whenever I’m out and about either riding my motorcycle or participating in racing events occasionally I see things that just make me wonder “why”? One of those moments is when I see someone take a cold bike and fire it up for the first time and bang it off the rev limiter, start riding it immediately, or annoyingly continuously blip the throttle as if it will never idle on its own.

These actions beg the question, “Why is it important to warm up an engine”?

The answer lies in a simple explanation of science and mathematics. Before you quit reading because you may not have been an ace at math and science in high school, just give me a minute to break it down. It is actually really simple.

The whole reason we need to let our engine warm up revolves around the concept of linear thermal expansion. Your engine is made up of a number of different materials. The piston is made from a certain type of aluminum alloy, the cylinder another type of aluminum alloy, the rings cast iron or steel, the valves if you have a four-stroke from steel, stainless, steel, or titanium, and the guides are made from yet another material. Once the engine is started these components begin to heat up from combustion and friction as they slide back and forth. None of these materials are exactly alike, and because of this they will expand when heated or contract when cooled at different rates. This interaction between material and change in temperature is predictable and linear.

Now that we understand that engine components change dimensionally from when the motor is cold to when the motor is warm we can start to see the importance of warming up the engine. When a cold engine is first started the piston heats up and expands first. Heat is transferred from the piston to the rings and then to the cylinder wall. If we rev the engine and generate lots of combustion cycles and increase the frequency of friction too early the piston will grow much faster than the cylinder. If there is not adequate space between piston and cylinder to account for this growth the engine could suffer what is known as a cold seizure and you will have yourself a bad day.

By allowing your engine to warm up before you start riding you allow all the components in the engine to slowly expand and stabilize. Once the engine is warm, changes in the engine part dimensions are less drastic and there is much less risk of damaging the engine.

The picture below shows an engine which was limped home after the coolant started leaking out. As the engine lost its ability to cool down, things began to tighten up. You can see how the piston contacted the cylinder evenly around the bore and created the vertical scuff marks.

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Even though this engine didn’t completely seize, you can imagine the severity of scuffing would be much worse for an engine that would seize.

So you are probably wondering, “how do I know when my engine has properly warmed up then?” and, “what exactly do I do to properly warm it up?”

The procedure for warming up the engine is simple.

1. Start the engine using the choke if necessary

2. Once the idle comes up due to the choke turn the choke off

3. Allow the engine to idle with the choke off until the cooling system warms up and the engine comes up to temperature.

Knowing when the engine is ready to ride is a bit subjective. As you begin to pay closer attention to your engine, you will begin to detect when it is ready to ride.

Personally for water cooled engines I like to feel the radiator and use that as an indicator. I place my fingers on the side of the radiator where the coolant is returning from the cylinder head and lightly touch to get an idea of how warm the coolant is. I do this until the radiator is just getting uncomfortable to touch. This typically only takes a few minutes and after that I’m ready to start riding the bike.

For air cooled engines my approach is much the same except I feel the cylinder and head to determine when I think the motor is warm enough to ride without causing any unnecessary wear or damage.

Paul

If you'd like to follow my blog, click the "follow this blog" button in the upper right. I'd love to have you. :thumbsup:

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I've often wondered how I could tell if my bike was warmed up enough.  Thanks for the tip.

I'm glad you found this information useful and I hope you continue reading and find future posts helpful as well!  If you have any specific questions you'd like me to discuss please let me know and I will do my best to work them into future blog posts. Thanks!

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What is the propper method to warm up KTM XC-W/EXC/SX (2 stroke) bikes?

I ask this because I have KTM 250 EXC european model, it is exaclty as KTM 250 XC-W, After 5 min of idle, the radiators are a little bit warm, not hot, I can rest my hand on radiators way long. Some friends of mine said that should I blip the throttle few times. Is that correct?

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Keep in mind that the heating up comes from combustion AND friction. The cylinder and head will hear up slower because there is not only more mass to hear than the piston but also they are the parts that are cooled (air or water). The cooling system is doing it's job by drawing heat out of the cylinder and head as soon as you start the motor. There isn't much to cool the piston besides the fresh fuel/air charge and it has less mass so it will hear up quicker. Bottom line is to wait until the cooling system comes up to temperature before flogging the motor. Usually around 170f+ or when the radiator is hot to the touch. If the bike has cooling fans they will usually kick in around 200-210f.

Also, Be careful not to boil over a bike with no overflow tank by letting it sit still for TOO long.

One final thing to consider is the engine oil will be thicker when it is cold. At very least you will be loosing some horsepower until it heats up and thins out. At worst you might have problems from lack of lubrication, but that's very uncommon...

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this is very true keep in mind that this is why you dont wash your bike while the engine id hot you want the parts to cool slowly. if you cool them down by spraying it with water you could possibly cool down the cylinder and it will shrink down with the hot and expanded piston inside it. i see alot of people come off the track and start spraying there bike before it has a chance to cool down.

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Good additional information 762SPR and levi534.  While everyone has their own method for warming an engine up what is most important to me is that folks understand the how and why behind it.  Once you understand the how and why you can begin to formulate your own opinions on the best way to warm your engine up.  As many powersport vehicles are different I offer my procedural advice for those just starting out that would like a basic method until they are able to get a feel for when their vehicle is ready to ride.

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this is very true keep in mind that this is why you dont wash your bike while the engine id hot you want the parts to cool slowly. if you cool them down by spraying it with water you could possibly cool down the cylinder and it will shrink down with the hot and expanded piston inside it. i see a lot of people come off the track and start spraying there bike before it has a chance to cool down.

 

What about us off-road riders, who might go from running hot down a trail to dropping into a deep creek bed? What's the risk of damage in this scenario? I know that I've soaked my engine pretty good in the heat of battle with cold, mountain water. I've never had an issue, but that doesn't mean others have not.

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What about us off-road riders, who might go from running hot down a trail to dropping into a deep creek bed? What's the risk of damage in this scenario? I know that I've soaked my engine pretty good in the heat of battle with cold, mountain water. I've never had an issue, but that doesn't mean others have not.

i would think that going from running on the track to shut down and hosing off has a greater chance of doing harm than taking a running bike through a 40* creek. if the bike keeps running it should maintain the heat and not cause any adverse issues.

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Really? Dirt bike, Street bike, car, truck...Let the oil flow, let the metal heat up....Where is the mystery? IC engines of all types need lubrication and are designed to run best warm. Use good oil. Let the machine run until it sounds ready. Expect more warm-up time when it is colder. I live in the central Colorado Rockies where even summer temps can be cold, and occasionally really damned hot...Kick or switch yer bike on first, let it run at choke-off idle while you are changing into your gear, then let 'er rip!

\

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You didn't mention engine oil.

 

The engine is designed to run on oil of a particular viscosity. That "10w40" only is at the proper viscosity when it it at the correct temperature. When your engine is cold, the oil is too "thick". The result of this is that quite a bit (maybe most) of your oil is going through the oil pressure bypass valve. If you start and then just race off on a cold engine, your motor is not receiving adequate lubrication to vital internal components, such as the cam lobes, etc.

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On every bike I've ever owned, dirt or street, including my aircooled '74 Yamaha RD350 2-stroke, I fire up the engine, let it idle for maybe 3 minutes while feeling the cylinders for heat. Once I feel any kind of warmth, I hit the road .. or trail. I don't go full bore to redline, or even go heavy on the throttle - I take it real easy for the first couple miles, until everything is nice and hot. The bike will always warm up faster riding it than idling - same is true for cars/trucks. I was always the only guy out of all my buddies that didn't need to rebuild or re-ring his 2-stroke after 2 straight years of severe abuse, so I must be doing something right. ;)

 

As far as river crossings go, the same priniciple applies - crossing a 40° river with the cylinder submerged is going to lower your operating temperature a bit, but it's not going to cool down the entire engine, cases, or oil to ambient, especially when your still running. I've crossed some pretty cold rivers in winter - below freezing easily - and I've never had a failure. Lots of times I'm nearly full throttle to make it through too. Warm up, in my opinion based on years of wrenching on & rebuilding engines of all kinds, is far more important to engine life than a brief cold water contact. Out of all the people I've rode with that treated their equipment MUCH worse than I, I still have never heard of an engine failure from cold water .... at least cold water that remained outside the airbox, anyway.

 

Just my .02 ..

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I don't think that anyone that I work with (lots of folks) warms up their car for more than 30 seconds before driving home. Is this irresponsible? There must be a lot of cars that are harmed daily if that is the case.

 

 I'm not saying we, or they, shouldn't warm our engines up thoroughly, just an observation.....

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