Frequently Asked Questions
Is it FAA certified?
The Cool Jugs liquid cooled conversion kits are not FAA certified
and are for experimental use only.
We have put our plans to certify the CoolJugs conversion on
hold until such time as we can establish an economically viable
demand in the certified aircraft market. Several years ago,
the FAA announced substantial additional certification burdens
for piston engines that require more than double the legally
defined testing requirements specified by FAR 33 in order to
certify an engine. These additional, arbitrary requirements coupled
with draconian limits on initial TBOs make FAA certification
of CoolJugs conversion an expensive proposition. These additional
burdens plus the fact that each and every aircraft installation
would also require a separate installation certification essentially
makes it economically impossible to produce a certified version
of the CoolJugs conversion without the support and commitment
of a major certified manufacturer.
the complete lack of interest by certified aircraft manufacturers
such as Cessna, Mooney, Solaris, Lancair, Cirrus and others we
will be concentrating our efforts on developing complete installation
solutions for various popular experimental aircraft. If you really
want advanced, liquid cooled piston engines in type certificated
aircraft then you should ask the companies that make new airplanes
in the first place. Until the OEM aircraft manufacturers believe
that there is a demand for something more advanced than 1930s
engine technology they will not offer anything else.
For those of you that feel it might be possible to obtain a
field approval for the CoolJugs conversion on a certified aircraft,
you should know that there are substantial operational limitations
specified in both the FARs and in internal FAA Orders with regards
to converting and operating a formerly type certificated aircraft
in an experimental mode. Believe me we already know this with
our Cherokee conversion. Due to the (perceived) complexity of
the modifications both to the engine and the airframe it is highly
unlikely that the FAA will ever grant someone a field approval
for a CoolJugs conversion to a type certificated aircraft.
...and the good news?
The good news is that we are going to spend the money that we
would have otherwise wasted on FAA certification on developing
improvements for these engines that will go well beyond just liquid
cooling. We will incorporate the best of the last 50 years of
engine technology into these engines to produce the most advanced
and reliable piston aircraft engines that have yet to see the
light of day.
Is the Converted Engine Heavier and if so, How Much?
Everything possible has been done to reduce the additional weight of the conversion. First you should consider the weight of the air-cooled components that would be removed. The liquid-cooled cylinders are actually each about 1/2 lb lighter than the air-cooled cylinders. On a typical 4 cylinder engine this would amount to a weight savings of around 2 lbs. Removal of the air-cooled engine baffling usually reduces the weight by another 2 to 3 lbs for a total weight savings of around 5 lbs.
The typical system requires around 2 1/2 gallons of coolant
which, at 8 lbs/gallon weighs a total of 20 lbs. The rest of
the additional weight consists of the radiator (typically around
8 lbs), coolant pump (7 lbs), the coolant manifold (1 1/2 lbs),
thermostat housing (1 1/2 lbs), hoses (3 lbs) and miscellaneous
installation hardware (2 lbs). The net weight gain of a converted
4 cylinder engine (including a radiator) would be around 38
lbs, 9lbs of which can be offset by converting to a lightweight
starter and another 4-5lbs by converting to a lightweight alternator.
We feel that the small weight gain is more than offset by all
of the benefits that liquid cooling has to offer. Besides, using
9:1 compression pistons will boost horsepower on a typical O-360
engine from 180 to 195. That extra 15 horsepower more than offsets
the 20-30lbs of weight gain on a typical installation.
You should also consider the potential for significant reductions
in cooling drag that are possible with a liquid cooled engine
installation. An extra 10-15 knots is possible on an aircraft
that would otherwise cruise around 160 knots with an old fashioned
air cooled engine.
Finally lets not forget the very real fuel savings. We're not
talking about a measly 5% or even 10%. We are talking about a
in fuel savings!!! However, not only do you get to save fuel
when running at full power, but you also get more power since
the combustion gases are not being cooled by running at full rich.
Will it work on a Fuel Injected engine?
Yes! Our cylinders have the necessary ports to install the standard
Will it work with a Turbocharged/Turbonormalized engine?
It sure will. In fact any turbocharged engine will benefit greatly
from being converted to liquid cooling. As almost anyone who owns
and operates a turbocharged air cooled engine will tell you -
managing the temperatures of their engine is crucial to keeping
it out of the shop. However, even the most careful pilot cannot
do anything about the even shorter TBOs that are a fact of life
on all turbocharged engines.
If you are planning to build an experimental aircraft with a
turbocharged/turbo-normalized engine you should also consider
the benefits of using a liquid cooled turbocharger. Yes they do
exist and they can offer some substantial benefits both from a
convenience standpoint (no more waiting for the turbo to cool
down before shutdown) and from a maintenance standpoint.
What is used for the coolant?
The coolant is typically a 50-50 mixture of water and some type
of glycol (antifreeze). We do not recommend greater than a 60/40
ethylene glycol water mixture. Since we require changing the
thermostat and coolant at least every 5 years or every 1000
hours of operation, whichever occurs first we are concerned about
the environmental impact of disposing of ethylene glycol which
is highly poisonous and non-biodegradable.
Our only major requirement for the antifreeze is that only
non-phosphate glycols are approved for use in
our conversion. Use of any glycol containing phosphate - no matter
how little will void the warranty and we can guarantee that your
aluminum radiator will plug up in a matter of months. Phosphates
and aluminum just don't go together. Today virtually all commonly
available anti-freeze brands are non-phosphate. Any anti-freeze
glycol that meets or is certified to meet Dex-Cool specifications
is supposed to be phosphate free.
As an alternative to ethylene glycols and in order to protect
both the environment and our Cool Jugs conversion we recommend
the use of propylene glycol in at least a 60/40 mix of propylene
glycol and water. Since propylene glycol is both an environmentally
friendly, non-poisonous and bio-degradable substance and has
unique thermal qualities it is a better overall antifreeze compound.
We are planning further testing to determine the potential benefits
of running 100% concentrations of propylene glycols.
For more information on propylene glycols you should visit the Sierra
What about the O-320 engines?
Yes, we are already planning to offer a conversion for the O-320
engines. However, we are going to wait until we sell a few O-360
and O-540 conversion kits first.
Are there any plans to liquid cool Continental engines?
Yes, we know that Continentals have their problems especially
in the valve train and cylinder head. Unfortunately we don't have
any immediate plans to offer a liquid cooling solution for Continental
engines. One of the most difficult aspects of converting a Continental
engine is finding a place for the water pump.