I will wrongly intermix the terms "weight" and "viscosity" for oils in the following - but you will get the idea!
Certificated engines usually come with a requirement to preheat if the temperature is 20F or lower.
In the days of single weight oils that turned to jelly in the cold - there used to be an old trick of adding a pint of AvGas per 4 quarts of oil in the sump and pulling the engine through to mix it all and dilute the oil prior to starting. As the oil warmed the AvGas would boil off through the crankcase breather....
Modern multi-weight oils get around this by being thinner in the cold and stay thick in the heat. But even a 20/50 will start to turn to jelly when it gets cold enough.
--
To take the AeroVee as an example - I am sure running around the streets of Germany in a VW Bug in the winter - a cold start where it took a while for the oil to warm up and really lubricate was not an issue. Worst that happened was the engine wore out early. In a plane?....
--
So I use 32F as my decision point. If the plane has only just got down to that - the engine will start fine. If the plane has been cold soaked overnight and the temperature is just coming up on 32 - I DEFINITELY preheat. A little of "Mr Red Dragon's" breath, gently applied to the sump and allowed to rise up through the engine compartment and contained by an insulated blanket will get the engine toasty in about 30-40 mins while I do a methodical pre-flight. I wait till the front cylinders no longer feel "cold" but they don't need to be hot either. Just enough to not feel like cold metal.
Added benefit - the battery will be warmer and livelier!
--
Note - Red Dragon suggest blowing in through the front cowl openings to get the cylinders warm. That's what you will get from a "Winter FBO" that give pre-heats as a service. That works - it's the short cut way of getting a start. But it doesn't take care of the cold oil in the sump and the rest of the metals in the engine. I'm paying for the engine - I'll take my time and gently pre-heat the whole thing. This just yesterday. After preheating use your WARM start procedure. Not a cold start procedure.
Keeping a big extinguisher handy in case you get a bit aggressive with the heat and light something off is a good idea.
--
Related Note - MGL's AHRS units do not work well in the cold. They do contain microheaters to get all the electronics up to temperature and tolerance - but can take 20 mins turn on time to do so. Don't depend on your AHRS till the horizon is demonstrably stable after the avionics have warmed up.
Posted: Thu Feb 10, 2022 12:22 pm