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#21
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The threat of the aluminum case shrinking to the point of seizing onto the
steel crank due to the differential in expansion rate of the two materials is more theoretical than real... Ignored is the fact that the bearing shells are steel cylinders and will compress only so much when the case shrinks, else they would buckle and collapse... The argument of "it is the liquid cooling that makes the difference", ignores the engineering fact that modern liquid cooled engines have vastly tighter clearances than air cooled engines, not the other way around... So, low temperature starts should be a hundred times more damaging to the engine on your car by that theory... Yet my aluminum block/steel crank automobile engine, which has such tight clearances that the owners manual calls for a 5W20 as the standard oil, - I actually use 10W30 - started the other morning at -14F yup, 14 below and is still running fine, no knocking, no oil smoke, no crushed bearing shells, etc... As I spoke about in my diatribe on preheating, yesterday; most of what is passed from cfi to student is an old wives tale endlessly repeated... And yes, some of those OWT's find their way into the pilots handbook from engineers who ought to know better... As far as the comment about cylinder choke - yup, it exists - but come on guys, think!... The cylinder sleeve is steel, the piston is aluminum... So the piston will shrink more than the cylinder at very low temperatures, not the other way around... There is no interference fit and no binding on start up... Let me post a challenge... Who knows of an engine that was actually damaged and had to be overhauled because of cold starts without a preheat? Nope, not the story of a guy I know told me about so and so... What engine do you have first hand knowledge of, that was burned up on your airfield because of a cold start? Doesn't exist! I can start my engine every morning all winter long with no preheat, and you start your engine once every two weeks with preheat, and I will have less wear on my engine than you will... denny wrote in message ... Dave Stadt wrote: : How come the engine in my car with 190,000 miles is running fine with no : signs of undue wear with nary a single preheat. It is often started at : temps well below 0 F. Aluminium block, steel crank, steel cylinder liners : and aluminium pistons same as the ole Continental. Two words: Liquid cooling. Everything about the aircraft engine is catered to running at ridiculously high temperatures during normal operation. The oil is very thick so it still lubricates at high temperatures and carries heat away from the cylinders. The cylinders themselves have choke (they're slightly smaller bore at the top), with the thought being they'll expand to be straight when they heat up during normal operation. Those two things are the primary reasons.... lack of oil and scuffing of cylinders. -Cory -- ************************************************** *********************** * The prime directive of Linux: * * - learn what you don't know, * * - teach what you do. * * (Just my 20 USm$) * ************************************************** *********************** |
#22
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Wasn't that the basis for a song about a beautiful woman and a desperate
man? denny "Doug" wrote in message om... Well,,,desperate men do desperate things. |
#23
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No No!
Ground running is NOT good for an engine. Uneven cooling, you know! Take it up for a 1 hour FLIGHT each four hours! That's the PROPER way to keep it warm. Rich Doug wrote: Well,,,desperate men do desperate things. Stay at a motel near the airport and go out and start your plane and run it for 1/2 hour every 4 hours. Bring the walkman. |
#24
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Exactly!
denny "Dave Stadt" wrote in How come the engine in my car with 190,000 miles is running fine with no signs of undue wear with nary a single preheat. It is often started at temps well below 0 F. Aluminium block, steel crank, steel cylinder liners and aluminium pistons same as the ole Continental. |
#25
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Dennis O'Connor wrote: As I spoke about in my diatribe on preheating, yesterday; most of what is passed from cfi to student is an old wives tale endlessly repeated... And yes, some of those OWT's find their way into the pilots handbook from engineers who ought to know better... Pilot's handbooks are written by marketing departments, not engineers. George Patterson A diplomat is a person who can tell you to go to hell in such a way that you look forward to the trip. |
#26
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Viscosity...
"Paul Sengupta" wrote in message ... wrote in message ... The oil is very thick Is there any difference in viscocity between a 15/50 aero oil and a 15/50 car oil? Paul |
#27
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As I understood it, the max engine damage is done just after starting,
before the oil is flowing properly, both in a car engine and a plane engine. I know when it's cold it takes longer for my oil pressure to come up, inferring that the oil is thicker when cold...also suggesting that the oil isn't flowing to the important bits so quickly. So I'd have thought that pre-heating (if done properly) would extend the life of the engine by some amount rather than prevent catastrophic failure. Paul "Dennis O'Connor" wrote in message ... Let me post a challenge... Who knows of an engine that was actually damaged and had to be overhauled because of cold starts without a preheat? |
#28
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wrote in message ... Dave Stadt wrote: : How come the engine in my car with 190,000 miles is running fine with no : signs of undue wear with nary a single preheat. It is often started at : temps well below 0 F. Aluminium block, steel crank, steel cylinder liners : and aluminium pistons same as the ole Continental. Two words: Liquid cooling. Everything about the aircraft engine is catered to running at ridiculously high temperatures during normal operation. The oil is very thick so it still lubricates at high temperatures and carries heat away from the cylinders. I use 15W50 in the Continental and 10W40 in the car. Not much difference. Also, in the winter people run their Cont/Lycs on straight 30 weight. 30 weight is like water when at operating temps. I don't believe my O-200 runs nearly as hot as a modern auto engine. The cylinders themselves have choke (they're slightly smaller bore at the top), with the thought being they'll expand to be straight when they heat up during normal operation. Those two things are the primary reasons.... lack of oil and scuffing of cylinders. Doesn't play. The pistons are aluminium and the bores are steel. In cold weather the aluminium pistons shrink more than the steel cylinders and clearance actually increases. The rings are steel and follow the cylinders. -Cory -- ************************************************** *********************** * The prime directive of Linux: * * - learn what you don't know, * * - teach what you do. * * (Just my 20 USm$) * ************************************************** *********************** |
#29
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well, I've done the no-preheat thing on a 30 degree day and the prop
didn't spin all that fast (barely started). With a preheat on a 20 degree day the prop spins a lot faster. Preheating does something for my engine. Ditto that. We've got the oil pan and cylinder heaters, and a cowl blanket. Pre-heat, and the thing pops right over. Don't pre-heat, and it cranks like an old meat grinder. Which sounds like a friction thing to me. And I guess I always assumed that friction was a bad thing inside an engine. -- Jay Honeck Iowa City, IA Pathfinder N56993 www.AlexisParkInn.com "Your Aviation Destination" |
#30
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Double ditto.
I want fluid oil running all over those freezing cold engine parts. Whether engine clearances are reduced when cold or not, metal on metal with no lubricant can't be good. I would not expect catastrophic failure. Just reduced engine life. Next time I see some poor soul at the side of the road with a smoking engine, I'm gonna think - cold engine starts. -- ------------------------------- Travis "Jay Honeck" wrote in message news:CivYb.339528$xy6.1678994@attbi_s02... well, I've done the no-preheat thing on a 30 degree day and the prop didn't spin all that fast (barely started). With a preheat on a 20 degree day the prop spins a lot faster. Preheating does something for my engine. Ditto that. We've got the oil pan and cylinder heaters, and a cowl blanket. Pre-heat, and the thing pops right over. Don't pre-heat, and it cranks like an old meat grinder. Which sounds like a friction thing to me. And I guess I always assumed that friction was a bad thing inside an engine. -- Jay Honeck Iowa City, IA Pathfinder N56993 www.AlexisParkInn.com "Your Aviation Destination" |
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