Mr. Claude McKibben is the owner of a 1977 Hawk XP R172K based in Rochelle, Illinois. He uses his airplane approximately 75 hours per year split about evenly between business/personal. The engine in this airplane is a Continental IO-360-K. The following significant events appear in engine and airframe logbooks:
- Tanis TAS-100 preheat system installed in December 1980 at 777 engine hours.
- Schneck Aviation in San Antonio performed a major overhaul in 1984 at 1,541 engine hours, and reinstalled the original Tanis preheat system on the rebuilt engine.
- Mr. McKibben became the owner of the Hawk XP in July 1989 with 2,030 airframe hours.
- In August 2011, he delivered the aircraft to the Continental Motors factory service center in Fairhope, Alabama, for installation of a new IO-360-KB. The original engine was at 1,890 hours SMOH by Schneck.
- During installation, a decision was made to install a new Tanis preheat system.
- On removal of the previous IO-360 engine, compression readings revealed one cylinder in the high 70s; four cylinders in the mid to low 70s and one cylinder in the low 60s. The engine was reported to use about one quart of oil every 10 to 12 hours with fuel burn at 9.3 GPH.
- After 31 years and 2,654 flight hours, the first Tanis preheat system was removed from the original engine and returned to the Tanis for inspection and evaluation.
Mr. McKibben made the following statements regarding his operation of the Tanis preheat system:
- Over its installed lifetime, the TAS-100 preheat system only required replacement of one cylinder heat element. “I could always depend on it to bring the engine to reasonable starting temperature, even when tied out.”
- The airplane was kept in an unheated hanger. Preheat was used at temperatures below 50 degrees F. A standard settable clock timer was used to turn on the preheater prior to departure. One to two hours of preheat was used at 50 degrees F.
- For colder ambient temperatures the length of preheat time was then increased proportionately down to zero degrees, or lower (occasionally as low as minus 20 degrees F), at which time a full three to four hours of preheat was used along with an insulating blanket.
- Although the User Guide recommends six hours of preheat before engine start, Mr. McKibben rarely needed that long in the hangar with the cowl plugs in place.
- Physical touch was used to ascertain adequate warmth of the engine prior to start. Oil was changed every 25 to 30 hours of operation.
Reasons expressed by Mr. McKibben for specifying Tanis preheat:
1. Good for the engine.
2. Ease of starting.
3. Minimize departure time on the ground.
4. Efficacy of Tanis design in delivering low levels of heat to all critical engine components and fluids.
Upon inspection of the 31-year-old preheater wiring harness, threaded heat elements and pad heat elements, the results were as follows:
- There was no abnormal wear noted on any of the cabling. Voltage and resistance checks were made on all of the cabling and found to be nominal and in accordance with new specifications.
- There were five TAS-100 threaded heat elements installed on this engine. The cylinder used for the factory CHT probe did not have a heating element installed. Of the five threaded heat elements, four were found to be nominally functional and in accordance with original factory specifications regarding resistance and ability to produce rated heat output. A single threaded heating element was found to be not functioning.
- Two heat pad elements were part of the system, one affixed the lower underside of the engine case and one affixed to the topside case. Both of these pad elements were found to be functional.
CONCLUSION: Even though only four of the six cylinders had heat applied to them for reasons mentioned above, Tanis feels that the operational technique used by Mr. McKibben as described above resulted in a long-term satisfactory outcome in the use of the Tanis preheat system. Using a blanket to contain heat in an unheated hangar, physically checking the engine for warmth prior to departure, regular interval oil changes and being diligent about preheating were (and are) responsible for achieving the inherent benefit of the Tanis preheat system.