Article: Bye, Bye Blowpot!

  • Oil Dilution-Mol-K-78-179
    by Rex Terpening

    While rummaging through some old files recently, I came across some historic pieces of paper–these being notes and sketches that I made many years ago on our first, primitive oil dilution installation.

    This activity took place in Winnipeg, Manitoba in 1939. At that time “oil dilution” (to give it a formal title) was a rather revolutionary idea and attracted much interest (and probably a measure of disbelief!). The initial idea–a method of cold-starting aircraft engines by diluting the lubricating oil with gasoline–came from an unlikely source. It was the subject of a paper presented to a group attending a Society of Automotive Engineers (SAE) Conference in New York in the winter of 1937/38.

    The originator of this idea was Mr. Weldon Worth, a professional mechanical engineer and civilian employee of the U.S. Air Force. The reason behind the proposal was the possible need, by the Air Force, of a method that would permit their fighter aircraft to become airborne quickly without engine pre-heating. It would seem that the Air Force had shown no immediate interest in Mr. Worth’s proposal because, it is assumed, he was given permission to present the idea in a paper to the SAE. Obviously the thought never occurred to the Air Force Chiefs that they might be required to operate fighters, bombers and transport aircraft in winter conditions. One of those attending the SAE conference was Tommy Siers, Aircraft Maintenance Manager for Canadian Airways Ltd., of Winnipeg.

    Tommy immediately recognized the potential value of such a system. Canadian Airways, with a winter-operating fleet of roughly 40 aircraft, practically “lived by the blow pot” during half of the year. Winter flying in Canada had only become possible by the simple expedient of draining the oil each night, preheating both engine and oil the following morning, then re-installing the oil. This was a time-consuming, laborious, and at times, hazardous job. A new system would be a huge benefit to all operators–both civilian and military.

    Following his return to Winnipeg, Siers arranged a meeting with Canadian Airways President, Mr. James Richardson. He presented an outline of what he had learned and of the safety improvements and cost savings that should result. Mr. Richardson immediately recognized the potential benefits and authorized the development and installation on one aircraft.

    A Norseman aircraft, CF-BDC, became the first aircraft, ever, to be equipped with an oil dilution system. In spite of obvious interest in this development from all participants, on her first trip after freeze-up, CF-BDC went through the ice–and was out of service for the balance of the 1937/38 winter season. CF-BDC lost her claim for a lasting place in Canada’s aviation historical records.

    Oil Dilution-Norseman IV CF-BDC-RAMWCCopyright

    After losing an argument with a Jacobs-powered Waco at Yellowknife in the fall of 1938, I paid a visit to our Brandon Avenue shops and was offered a transfer to Winnipeg. I arrived in January 1939.

    I was assigned to work on the oil dilution system that was being installed on Junkers aircraft, CF-AQW, with Jock McGeorge as my co-worker. I had never heard about oil dilution and I had my doubts about the possible success of this far-out idea. Jock was of a similar mind.

    One of the key features of this system was an extensive modification to the inside of the oil tank, thus creating two separate oil-circulating systems. I expressed my doubts about this new development and was told: “The oil dilution part of it should work OK. The starter, the priming system and the spark plugs will probably give us trouble.” This was a prophetic comment and such proved to be the case.

    With the installation complete on the Junkers, we took CF-AQW to Stevenson Field to put theory into practice. A routine test flight was carried out with Pilot Bill Catton. The machine was left standing overnight with oil in the tank.

    When we arrived at the airport the next morning, it was a typical Winnipeg winter morning–a temperature of -30°F with a stiff breeze blowing. CF-AQW looked positively naked without her customary engine cover. To my surprise however, the prop turned quite freely, but my optimism soon vanished. It developed into a morning of frustration and hard work. It was early afternoon before we had the motor running.

    Finally, with the engine running and the oil pressures and temperatures approaching their normal readings, we shut down the motor for a general inspection and were pleased with our findings. The main body of oil in the tank was still stone cold–even though the oil-in and the oil-out temperature readings had been normal. In other words, Mr. Worth’s theories were practical. The transfer of heat from the diluted oil to the main oil in the tank was preventing the oil from over-heating and, at the same time, it was warming the main body of oil.

    The dilution system was working as planned. However, we still struggled with it; we had a series of problems with the primer, starter, booster magneto and a faulty gauge. Initial improvements consisted of: a) installing a larger primer, b) adding additional primer jets (and these of an improved design), and c) changing the starter (installing a direct-cranking starter in place of the electric/inertia that was originally used).

    With these improvements, we were able to obtain consistent starts after overnight, sub-zero temperatures. We were now “born-again believers” and anxious to demonstrate our new-found technology to the uninitiated. We headed for our nearest operational base at Lac du Bonnet.

    The temperature in Lac du Bonnet, Manitoba was normal for late winter; -15ºF with a 20 mph wind. We landed just before noon, diluted the Junker motor and shut it down. The base crew was reluctant to leave the motor uncovered while we went for lunch. However, we all retired to the local restaurant and spent the time trying to convince the crew of the wonders of oil dilution. We returned to the aircraft and, in front of our doubting audience, we achieved a perfect start on our first attempt.

    Now, you may believe the oil dilution system was fully functional and only needed minor refinements. This, however, was not the case. We still had starting and dilution problems. Our dilution valve was a manual affair and we had recurrent leakage problems, due to a lack of the proper type of seals. An ignition coil that was controlled by a manually controlled “on/off” switch replaced the booster mag. The starter control was changed from a hand-controlled switch to a foot-operated switch because we soon realized there weren’t enough hands to go around during the engine-starting attempts.

    Another recurrent, early problem was oil that was being discharged from the crankcase vent. The overly thin oil was not able to withstand the combustion pressure in the cylinders. This “blow-by” would increase the crankcase pressure and the resulting oil/air mixture would discharge through the crankcase vent fitting. In extreme cases (and these were numerous in the beginning) the oil would be deposited upon the windshield, somewhat to the consternation of the pilot. In order to direct the oil to other–and less vital–locations, a vent tank was added and the crankcase vent connected to this.

    The correct amount of dilution for an overnight stop was always a guessing game and was more art than science. If the anticipated overnight low was -15ºF, a dilution period of perhaps three minutes might be used. Engine covers and a blow pot were still carried as a precaution. In a reverse of the above situation, one ended up with a slightly (or in some cases considerably) over-diluted engine. The only solution to this was a prolonged warm-up period to burn off the dilution.

    I left Winnipeg the following summer and had no further direct experience with the development of the oil dilution system. I do know that Canadian Airways Ltd. continued with their fleet conversion and used the system extensively over the coming years. The system was incorporated into the big Junkers, CF-ARM. The Norseman fleet was modified, as well as the Wasp-powered Junkers W-34s, as well as the Beech 18s.

    Further development of the oil dilution system came to a halt with the beginning of the War. The American military had been paying close attention to our activities and realized the benefits. I believe an oil dilution system was included in the specifications for all of the military transport aircraft that were then in production–Lodestars, DC3s, C-46s and others. The cold-weather operating instructions published by the Canadian Department of National Defence and the FAA also included instructions on the use of oil dilution. I doubt Mr. Worth ever received any substantial credit or recognition for the development and widespread use of what was then a revolutionary idea.


    Rex Terpening is one of the very last of a breed of air engineers who flew with the bush pilots and shared all of the routine hazards they faced. Rex joined Canadian Airways Ltd. (CAL) in 1935. In the late 1930s he was part of the team involved in the development of the Worth oil dilution system. Although the first initiative failed, the system ultimately became so successful that by the early 1940s, every aircraft in CAL’s fleet that was capable of using the oil dilution system was equipped with it.

    The top photo is a rare image from Ken Molson’s book Pioneering in Canadian Air Transport. It shows Canadian Airways Limited pilot W.E. Caton doing the dangerous job of heating engine oil over an open-flame blowpot at Gods Lake, Manitoba, 1935.
    This article was originally presented as a series of three columns in the 2006/2007 editions of Altitude.

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  • oil

    Thanks for this useful information

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