Idling... Why is it so bad?
- Thread starter Ron-Indy
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I keep hearing about condensation. Where is it coming from? Cold air holds little to no moisture. Fuel does/should not have any water in it. Where is the moisture coming from?
Well the combustion process produces moisture and also there is constant circulating of air thru the oil system via the pvc valve so the warm air inside the pan (picking up combustion products including water vapor) touches the cooler wall of the pan and condenses water. That's merely speculation and a little of knowledge on my part.
I thought the purpose of the PCV (positive crankcase ventilation) was to provide an outlet for positive air pressure in the crankcase which comes from blowby. The positive air pressure is routed back to the intake to be burned. Your quote makes it sound like there is fresh air introduced to the crankcase, which is not true, at least on the engines I have worked on. Please clarify.
Also curious about how combustion produces moisture. I don't disagree, just curious.
Water is a byproduct of the chemical reaction of combustion.
uh, i wouldnt nessassairly say water is a byproduct of combuation, but water vapor perhaps. and if your rings are doing their job, most if not all of it should be blown out the exhaust valves.
maybe a clue to this. i know when i still had my cat installed, and was up north, every morning i would start the car water would trickle out the tailpipe. sence i removed the cat from the exhaust, water no longer comes out, only a small ammount of steam, and only for a short while.
so maybe water gets in the block when the engine is shut off, and is cooling down? perhaps the hot air and oil inside the engine shrinks in size and pulls cooler air into the crankcase where it condenses to form water droplets?
water can only form where water vapor is present.
maybe a clue to this. i know when i still had my cat installed, and was up north, every morning i would start the car water would trickle out the tailpipe. sence i removed the cat from the exhaust, water no longer comes out, only a small ammount of steam, and only for a short while.
so maybe water gets in the block when the engine is shut off, and is cooling down? perhaps the hot air and oil inside the engine shrinks in size and pulls cooler air into the crankcase where it condenses to form water droplets?
water can only form where water vapor is present.
The principle might be the same, but in practice the result is vastly different. Modern fuel injected engines only need to be rich enough to keep the engine running with no load. With the help of the throttle postitioners they use to increase the idle speed, they don't need to be very rich at all.quote:
Originally posted by Bamaro:
Whether it is a new fuel injected or an old carburetor & choke engine, the principle is the same. Cold engines run rich.
The sooner they get up to operating temperature the better - for the engine, for your gas milage, for the air.
The fastest way to get the engine up to operating temperature would be to run it WOT with a heavy load. I think we could agree, that's a bad idea.
So given the original question was "why is it bad to idle an engine?", I'm going stick with what I said before. With adequate oil flow and pressure, it's not. The worst things are - You'll use some fuel since you'll be getting 0 MPG and it will skew your OCI because we typically use miles instead of hours to decide when to change oil...
[ December 20, 2003, 12:45 PM: Message edited by: jsharp ]
[C(H)2n+2]+ O2= C02+H20
Fred...
Fred...
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Addressing the water vapor issue-We did a totally unscientific experiment with some police bikes that were rusting out their exhaust systems. Here in the moisture laden mid-atlantic, there is a ton of water vapor in the air (humidity runs >70% most time). We parked 2 bikes after being run, one inside the heated garage, one outside. The next day on start-up, the outside bike would produce visible vapor in the exhaust while the inside bike produced almost none. Repeated the procedure again and then the next day we removed the exhaust systems and the heads. We found noticible water droplets in the exhaust of the outside bike especially near the exhaust port of the head. Water droplets on the piston crowns and exhaust valves/ports. We theorized that the cooling of the hot exhaust would draw in cooler/moist air and reach a "dew point". Since there was really no way to expel this air while it sat, it would precipitate out as droplets. Water vapor was also entering through the intake system and creating some droplets as well but not nearly as much as the exhaust side. This supports Al's thoughts on condenstaion inside the engine itself. Water vapor can and will find its way into the crankcase after shut-down but certain engine designs are better at keeping it in check than others. We finally solved our problem with stainless steel exhaust systems and parking the bikes inside.
Okay, I posted the UOA's that I mentioned in my previous post. I would've posted more, but I got sick of typing
http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic&f=3&t=001118
http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic&f=3&t=001118
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