On 10 Nov 2004 23:37:55 GMT, (PaulaJay1) wrote:

Winter is comming to Ohio ( thou the 60 deg day today disagrees) and the
subject of engine preheat arrises. I have a Tannis for the cylinders and a pad
to heat the oil. I can call the FBO and have them plug it in an hour before I
arrive and the engine is, at least, not cold to the touch. Still there is the
time when I fly somewhere for dinner or overnight and park in the cold, cold
outside.

The question, why is preheat necessary?

If it is OK to start the engine cold when the temp is 60deg F and let the cyl
head temp go up to 500 or 600 deg, why is preheat recommended when the cold
temp is 10 or 20 deg? The percentage difference in the delta T is less than
10%. Are the engine parts that critical that this small percentage change
makes that difference?

I use 15/50 oil so the "cold" oil should be a good at the lower temp.

Chuck

Getting oil to flow easily is only one part of the problem. As you note,
this can be "solved" with a multi-viscosity oil.

But another important factor is the clearance between the pistons and
cylinders (or, more specifically, between the steel and aluminum parts of
the engine). Because of the differential expansion/contraction of the
different metals, at cold temperatures, clearance may be non-existent, so
there is markedly increased wear until the engine gets above some critical
temperature.

There's some good information on the Tanis web site.

By the way, I hope you didn't really mean to have CHT's 500-600°. Most are
redlined below that level.

Also, I would question whether one hour on the Tanis is long enough -- I
thought I had read someplace that three hours was advisable (with an
insulated cover) but I could be wrong.

I just leave my a/c plugged in all winter (in Maine). CHT's are usually
around 100°F and oil about 80°F and it starts up as readily as if it were
summer.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)