Introducing Liquid Cooled Conversions for O-360 and O-540 Lycoming® Engines

Frequently Asked Questions
Technical Specs
Pricing & Warranty


Coolant jacket Cylinder head
Cylinder liner
Thermostat housing
Coolant Pump
Coolant Distribution Manifold
Cooling System Analyzer

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.

Sadly, given 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 whopping 38% 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 fuel injectors.

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 Antifreeze website.

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.


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