At this time of year, pilots are wondering about winter oil and what is the best practice for their airplanes.
Many pilots are still confused about when, where — or even if — they should use a multigrade oil. They also wonder whether they can go back and forth without harming their engines.
Whether or not to use a multigrade oil depends or several factors.
For example, if you live in a warm climate where it rarely freezes, then you can get by with single grade oil if you wish, or you can use a multigrade oil year around.
If you live in a southern climate, but fly north several times during the winter, you should consider using a multigrade oil in the winter.
There has been a lot of discussion about the belief that you should never change from a single grade to a multigrade oil or vice versa. In my experience I have not seen any long-term negative effects from changing.
However, there can be some short-term effects you may notice. The oil consumption can change quite a bit when you change from a single grade to a multigrade or from a multi to a single grade. It depends on how your engine is burning the oil.
In general, a multigrade oil will REDUCE the oil consumption past the rings from 30% to 50%. But it will INCREASE the oil consumption past the intake valve guides and/or through leaks.
The result is that oil consumption can go up or down when you switch the type of oil you are using.
The good news here is that in all of the engines I have monitored, the oil consumption goes back when the grade is changed back.
The other change I have commonly seen is oil temperature. Normally a multigrade oil will increase flow through the oil system and may result in a lower oil temperature. Since oil temperature is relatively critical, you should monitor the temperature closely and take steps if it does not get up to 170°-180°F range during cruise.
Water condensate is more notable in the winter and you need to get the oil temperature up so that the moisture can be boiled off during flight.
So Which Oil Should I Use?
If you live in the mid-continent area, a multigrade oil in the winter is a good idea even if you keep your plane in a heated hanger. If you fly during the winter, many of your destinations may not have pre-heating services and a multigrade oil will give you an extra margin of safety.
Finally, for pilots in colder climates, it is more important to use a multigrade oil especially in the winter because of oil cooler congealing.
When we first started testing Aeroshell Oil W 15w-50 in Alaska, we put it into a few planes in this one fleet. When we came back a few months later, they were out of oil because they had put it in all of their aircraft because it eliminated oil cooler congealing.
A multigrade oil’s biggest advantage is low temperature pumpabilty and flow. This gives better cranking speed, better chance of starting, and most importantly, quicker oil flow to critical bearing and cam surfaces.
Many people have chosen to use a multigrade year round, but a lot of pilots prefer a single grade oil in the warm summer months. That is your choice.
But always remember that changing your oil at least every four months — or 50 hours with a filter or 25 hours without a filter — and ensuring your oil temperature is in that 180°F range during cruise are still the most important factors for getting optimum engine life.