Charon
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Re: Oil temps and usage comparison
Reply #211 - 10/29/10 at 18:41:52
Well, gents, I have made a couple more trial runs, and found some interesting things.
Yesterday, 10/28/2010, I visited a local repair shop to get another oil filler cap, so I can destroy one and still have a cap in case I need the generator. While there I chatted with the proprietor (an old acquaintance), who told me of measuring oil temps on his old BMW 1000 boxer. He said there was available an oil thermometer which replaced the OEM dipstick, and on which he observed oil temperatures approaching 300 F. He mentioned Klotz, saying it got just as hot, but seemed to give him perhaps one or two mpg improvement. He also said Klotz was the only oil he ever used which made his BMW leak, and when he went back to petroleum oil the leak went away.
Based on Verslagen's IR temps for oil, I bought a meat thermometer with a high number of 220 F. I drilled the oil filler plug to a press-fit for the stem of the thermometer, and put the whole works on with the thermometer stem down in the engine oil. I also placed a piece of tape on the generator housing and made a pointer which I attached to the throttle butterfly. I marked throttle wide-open as 100%; throttle closed (to the idle stop) as 0%, and roughly divided the rest of the tape in 10% increments. Bear in mind this is a governed engine with no user throttle control, which is designed to produce somewhere near 60 Hz power, 3600 rpm.
My idea was to start the engine, and as soon as it came up to speed plug both my electric heaters into it and start the stopwatch. When I plugged in the heaters, the throttle solidly pinned against 100% and the engine bogged a little. I didn't like that much, so removed one heater for a moment. Then I figured to see what would happen, since the generator has an overload breaker. I started the stopwatch and plugged the heater back in. At start, the 10W-30 oil temp was 64. When the oil temperature reached 120, in about three minutes, the throttle began to drop. At five minutes the oil was 198 and the throttle had dropped to about 75%. I walked away for a few minutes. When I returned at twelve minutes, the oil temperature was off-scale, at an estimated 240, and the throttle had dropped to about 70%. At 17 minutes the oil was at an estimated 270 and the throttle was about the same. When the engine ran out of fuel at 29 min 25 sec the oil was perhaps 280. Temps above 220 are estimates, since the pointer was off-scale.
Conjectures so far. The oil viscosity decreases as the engine warms, and this is quite significant in terms of throttle position with a fixed load. In fact, it is a heck of a lot more significant under my test conditions than I would ever have guessed. Without casting doubt on Verslagen's measurements, either his Savage engine is cooled a heck of a lot better than the forced-air cooling on my Briggs, or the Briggs is working a lot harder than the Savage. Be it noted the Savage holds about 2.4 quarts while the Briggs holds 20 ounces.
I did some more experimenting today, but I am still digesting results.
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