What oil is best for winter?

Ben Visser


A few issues back, I wrote about what steps to take to winterize your aircraft (A chill is in the air: What does that mean for aircraft owners? Oct. 6 issue). Since that time several people have asked me the age-old question, "what oil should I use in the winter to best protect my aircraft?"

I am starting to feel like an old person, because every column seems to start with DEPENDS. Normally, I would just tell the pilot to use the same oil he normally uses. However, there are always some exceptions.

The three important factors are your climate, how long you will be storing your aircraft, and whether you plan to fly your aircraft and where you will be flying.

If you live in a warm southern climate and normally use single grade oil like a grade 100, then you can just stay with that same grade. The exception here is if you plan to fly into colder climates. If you will be starting your aircraft at temperatures at or below freezing, then I would recommend using a lower viscosity grade oil in the winter or switching to multi-grade oil, especially for flat engines. The advantage is that a multi-grade oil will provide improved start ability at cold temperatures but give improved viscometric properties at high temperatures (as compared to, say, a grade 65).

If you live in a colder climate and plan to fly your aircraft, then the same advice would apply.

If you live in a colder climate and do not plan to fly your aircraft, then you can just stay with the same grade of oil that you were using in the summer. Just remember to preheat thoroughly if you do decide to fly on a cold day.

A concern with operating with too high a grade of oil in the winter is oil cooler plugging. If you do decide to go flying, pick a fairly mild day.

Another choice for winter storage would be a preservative oil that meets the Mil-C-6529C spec. These types of oils are very good at preventing rust in an idle engine. If you are considering storing your engine for more than six months, especially if it is in a humid climate, I would recommend you consider using one of these products. These oils are straight mineral oil with an anti-rust/corrosion additive system. You can fly on these oils but, since the oils do not contain an ashless dispersant additive, I would recommend that pilots limit flying time on this type of product to 50 hours per TBO. These hours should not all be on one oil change. The oil works well if you fly zero to 10 hours during one change, then use an AD oil for the summer. This will clean the engine and you can repeat the cycle the next year.

If you think this process is confusing and expensive, I suggest you price a rebuilt or new engine. That should make the process worthwhile and make oil seem downright cheap.

Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at Visser@GeneralAviationNews.com.

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