| Re: [GMCnet] 2 interesting topics. Warming up your engine before leaving the drive. Piston travel. [message #326993 is a reply to message #326856] |
Sun, 10 December 2017 23:04   |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma:
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Matt,
Thanks for your response with regard to motoring (running by electric motor with no fuel to the engine), a gasoline automobile engine when it was cold to graph the friction to rpm factor. I was surprised to read that your experience that the friction was pretty linear. I have since looked on the net and found some engineers at MIT have done the same thing, and their graphs, both predicted and measured look much like a linear relationship with some mild upward curve until as you say pumping losses begin to rise quickly. I have also glanced at equations of total engine friction vs RPM and one factor does increase as the square of RPM, but it is only one of a number of factors, the others being linear, if I understand them. Real world experience as you have related to us is helpful. (I imagine you ran with throttle plates fully open?)
With reference to the comment by Jim K on never wearing an engine out but seeing them increase oil consumption. I have never worn an engine to the point that the oil consumption was over, say, 1000 miles per quart. Most were negligible. I don't like to burn oil. Not too religious about oil changing, but I do avoid high RPM if I can.
Got a story Chris, about a friend who bought a diesel over the road truck new some years ago. It used a 3208 Caterpillar engine. In the first three months, he cracked a piston. Took it back to the Cat dealer, and when he picked it up, he asked the dealer what he did. "Just replaced the piston." He said, "What, no boring, no honing, just replaced the piston and rings?", Dealer says, "Yes, you will be OK." He ran the truck 750,000 miles and sold it and it ran years afterward. So, even with diesel fuel having some lubricating properties, the high compression is no problem for it, as you say.
One more story. I have gone to China 12 times now, and remember the Volkswagen Santana taxis all over the place. Gasoline, manual shift. The first few times I rode in them, I had to bite my tongue. They short shifted them, first to about 7 mph, second to 12,skip to fourth and lug the engine up a ways and to fifth, to get the rest of the way to 35 mph. I confidently predicted to myself that they were beating the bearings out of the engine. I looked at the odometer, 270,000 kilometers. Other taxis were achieving like mileages. Got back from China last month, and on that trip they were doing the same thing. I figured more economy due to two factors, lower friction, and the largest factor, smaller pumping losses due to greater throttle opening. Fuel injected, ordinary cars otherwise. Four door midsize sedans.
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
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