Engine cracking in Cold?

[Fly boy]

Another Q from me that probably isn't worth posting but...

Its starting to get colder in the morning, and I was curious if I need to worry about the temp change. I start the bike, and let it warm up for not quite 5 minutes, then take off. I have some highway and some city driving I do, and when I get to school the bike is giving off heat at stop lights. My Q is...

Do I need to worry about the engine being hot from the ride, then turning off the bike and letting it sit in 40 degrees? I start it up an hour later to go to work, and it starts easy without choke. Will the heads crack, or anything like that?

Thanks an advance.

[Spiderman]

I'm not an expert, but I don't think you have to worry about that particular scenario.

I've only heard racers worry (because they run water + water wetter instead of anti-freeze) on weekends where the overnight temps are supposed to drop below freezing. The fear is that the water will freeze (and expand), cracking the engine.

[Fly boy]

ok, good enough for me.

[rybo]

I second spiderbob's post. As long as the antifreeze in your cooling system is in good shape this is not an issue at all.

I rode the VFR all winter last year, sometimes as cold as 11 degrees. No problems at all

Scott

[rforsythe]

You're fine.

[Fly boy]

Peachy, thanks guys. Now to check and see how the Fluid looks. Are Radiator flushes a good idea?

[Bassil Duwaik]

By: Paul Brand, Star Tribune
Three words: "time to temperature." In cold weather, our engines take a much longer period of time to reach full operating temperature. And they take this extra time each and every time we start them up, even if they have not fully cooled down.
Modern engine-management systems are very efficient at optimizing the fuel/air ratio entering the engine. The oxygen sensor monitors the percentage of oxygen in the exhaust, compares this with the percentage of oxygen in the atmosphere, and generates a low-voltage signal that communicates this ratio to the computer. The computer then adjusts the pulse-width of the fuel injectors -- the precise period of time each injector is open on each injection cycle --to fine-tune the amount of fuel reaching each cylinder.
The system makes this very fine adjustment dozens of times each second, working very hard to reach the optimum air/fuel ratio for any given situation, and at steady-state cruise speed seeks to approach the perfect ratio of 14.7 to 1, called the stoichometric ratio. The system is running in a "closed loop" when it is relying upon the oxygen-sensor signal to fine-tune engine operation.
But the engine-management system can seek this optimum air/fuel ratio only when the engine is up to full temperature. In fact, the computer does not look for a signal from the oxygen sensor until it approaches full temperature. During the warm-up cycle -- which takes considerably longer in cold weather -- the computer operates on a warm-up program based on coolant temperature, mass airflow or MAP sensor input of air volume and temperature, throttle position and engine rpm. This is called "open loop" operation, meaning the system is not operating off the feedback from the oxygen sensor.
In open-loop operation during the warm-up period, the engine requires -- and is provided with -- a richer air/fuel ratio to ensure good combustion.
It needs this extra fuel for the simple reason that a percentage of the atomized, then vaporized, fuel delivered to the engine condenses into liquid gasoline on cold internal engine components such as the intake manifold, intake valves, pistons and cylinder. And remember, it's gasoline vapor, not liquid, that burns.
Until those parts warm up, the engine needs more fuel to operate with reasonable drivability. Thus, the colder the weather, the longer it takes for your engine to reach full operating temperature and closed-loop operation, and thus the more fuel the engine uses to deliver the same driving cycle. That's the primary reason your engine consumes more fuel in winter driving.
Another factor in winter mileage is air density, defined as the number of air molecules per cubic foot of air entering the engine. Remember that 14.7-1 air/fuel ratio? That means 14.7 parts of air are mixed with one part of fuel for the perfect air/fuel ratio -- that's a lot of air!
In winter, colder air means denser air -- more molecules per cubic foot. At any specific throttle setting or opening, the same number of cubic feet of air, but containing more air molecules, will enter the engine. The computer will provide more fuel to create the proper air/fuel ratio at that moment. This is a bit more subtle, since "more air/more fuel" produces more power, so you may be able to operate at a slightly lower throttle setting -- sort of rebalancing the equation.
Found this article for you. Based upon this I don’t think that you’ll have any problems. After you turn your bike off it will cool slowly so it’s not a big deal. Now if you were to get water on the engine while it’s hot you could have some problems. Okay now I really got to get back to studying lol.

[rybo]

Interesting article, but a couple of important points to make.

1. Most modern sportbikes do NOT have an O2 sensor in the exhaust loop. The fuel injection system is a front end only type, so the O2 sensor arguement isn't valid with most motorcycles.

2. Fly's bike is an old school carbed version.

[Fly boy]

Thanks scott....

its JUST AN old school pos without Fuel Injection...




LOL j/k

[rybo]

Thanks scott....

its JUST AN old school pos without Fuel Injection...

your words, not mine.....

[No-coast-punk]

Interesting article, but a couple of important points to make.

1. Most modern sportbikes do NOT have an O2 sensor in the exhaust loop. The fuel injection system is a front end only type, so the O2 sensor arguement isn't valid with most motorcycles.

Not true at all. I can't think of a single modern EFI sport bike that doesn't have an 02 sensor from the factory.

The biggest danger that cold weather brings to most bikes that don't hibernate is oil leaks and increased engine wear. Oil pressure on a very cold engine is EXTREMELY high (at least 4-5 times higher at idle than nominal oil pressure on a warm healthy engine cruising on the freeway) during those first few minutes of running. If you do not let the bike idle long enough to get the oil warm and runny that extremely high oil pressure will start to blow past seals and gaskets over time. Once a seal starts leaking there is nothing that can be done to stop it.

The other problem is that the materials used in modern sport bike engines have a VERY big co-efficient of thermal expansion. When the engines are very cold everything shrinks a little bit and the tolerances get HUGE. I'm sure many of you have heard lots of piston slap and other scary clattering during the first few minutes of running during a cold day. Once things warm up all those noises go away. Problem is that the lubrication system isn't working as designed during those first few minutes.