Starting your piston engine in cold weather without a thorough pre-heat can damage it severely and drastically shorten its TBO. And according to cold-weather expert Ron Kensey of Kennon Aircraft Covers in brisk Sheridan, Wyoming, the key to an effective pre-heat is a quality engine cover.
February 9, 1998
Ron, what is the purpose of an insulated engine cover?
An engine cover helps retain engine heat or the heat applied to
the engine during pre-heating operations. A good cover can hold the engine heat for up to
6 hours so on a short stop over so you don't have to pre-heat again providing the first
thing that you do after shutting down is to throw on the engine cover.
If when you pre-heat you have a hot enough heat source, do you actually need an
Yes, and here is a typical scenario. You pay the FBO for what turns out to be a twenty
minute pre-heat from a powerful commercial pre-heater. The engine in the end is like a
rare steak, it is hot on the outside and cold in the middle.
What we are looking for is the effect of slow roasting... the engine cover is like a
roasting pan. It holds in the heat so it will be evenly distributed over the entire
engine. It is like roasting a turkey...we want the heat to penetrate evenly and thoroughly
so that it is warm all the way through.
You are making me hungry.
But you get the point. Pre-heating should be a slow process.
In Wyoming we do a lot of cold weather camping. We
have a large wall tent with a good size wood stove. It is not unusual to be either to hot
or too cold .... depending upon where you sit. An insulated tent would help achieve a more
That is what we achieve with an engine cover. A warm engine throughout...not just the
oil, or not just the cylinders, but the entire engine, including the front main bearing.
There are numerous pre-heating options and rationales. What do you think is the best
way to pre-heat?
The Tanis System makes good sense. Not only are you heating the engine oil but also
some of the cylinder block. The system is expensive and expensive to install and that is a
drawback. You can usually go from a cold soaked engine to a temperature safe enough to
start in about 4 hours with the Tanis System and a good engine cover.
Some of the oil sump heater distributors claim that their plug-in systems can
pre-heat a engine in four hours.
Certainly they will heat the oil in four hours, but it is the temperature of the
cylinders, bearings and pistons are more important. When an you start an engine with cold
cylinders, the aluminum pistons expand more rapidly than the steel cylinder, that is the
cause of cylinder scoring and excessive wear. You can do more wear in the first ten
minutes after a cold start then after hours of flying.
Perhaps heated oil makes it easier to start a cold engine, but then maybe it would be
best if the engine if it were not to start. I hear a lot of guys saying "I don't
pre-heat much, my engine starts right up." Starting a cold engine is not the point.
Preventing damage by not starting a cold engine should be the objective.
What should a pilot know about selecting an engine cover.
As with any cover the first thing you must do is assess the fit
and workmanship. I encourage customers to go out to the airport and compare covers.
Over 40% of our business comes from referral or from people who have seen our covers on
other planes, took down our telephone number off the label and call to place their order.
Price should be the last consideration. A less-expensive poorly-fitted cover is no
bargain. Neither is an expensive poorly-fitted cover. Start by looking at covers from a
distance and then up close. Then look at the label.
Some insulated engine covers are quilted, yours is not, how come?
Quilting destroys the loft of the insulation and therefore the insulating quality of
the cover is diminished. Quilting also puts needle holes in the fabric through which heat
can escape. The reason some quilt the insulation into the cover is to keep it from
shifting and bunching in the corners.
If you don't quilt your covers, how do you prevent the insulation from shifting?
Our process is to laminate the insulation to the nylon. It is so effective that we need
not quilt the cover and you can put it through the wash dozens of times without worrying
about the insulation shifting.
Do you use any of the high-tech insulating fibers like Thinsulate?
We don't use Thinsulate because it was designed more gloves, boots and clothing where
space is tight, it wouldn't do much good in an engine cover. We use the most effective
high-tech insulation available and follow developments in that industry as they happen.
How do your covers fasten onto the cowl?
The cover is split up the middle. The nose piece fits between the spinner and the cowl
and velcros together. Then we use a series of bungle with balls attached that stretch
through loops on the opposite side of the cover. This was something that Aviation Consumer
liked about our cover. The bungle and ball system is easy to use without removing your
You also make propeller and spinner covers. Do they help?
They sure do. The prop blades conduct the cold and dissipate the heat. Its like going
outside in the winter without a hat. The front main bearing is behind the spinner and the
prop blades conduct the cold through the crankshaft and to the main bearing. The rest of
the engine can be warm and loose while the main bearing is still frozen. That causes a lot
of wear and damage.
The front main bearing is expensive to replace. Its location and exposure to
the cold is another reason why you need more than just an oil sump heater. Prop covers
Let's face it. The propeller is the most critical flying surface on your aircraft. Prop
and spinner covers protect the propeller from ice, snow, blowing dirt and they are well
worth the modest investment.
How would you sum up your advice for cold-weather starting?
Pre-heat, pre-heat slowly, and use an insulated engine cover to retain the heat. Most
importantly, go out to the airport and look at various covers by different manufacturers
before you buy.