Preheat

On 11 Nov 2004 14:15:44 -0800, ) wrote:

A friend corroded the cylinders on his Cardinal from continuous
heating in just one winter. The water/acid boiled off the oil and
condensed in the cylinders on the bottom side.

He must have been doing something much different than I. I've been plugged
in all winter for the past fifteen years or so. The engine has been
overhauled twice during that time. No corrosion problems of the type you
describe.


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

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.

The differential expansion of aluminum vs steel is 6 microinches per
inch per degree F. Minimum bearing clearance is about .002 inch which
would take roughly 140 degrees of chilling to fully close up.
Probably even greater temps are needed for the cylinders to close up.
It is certainly a significant factor, but the reduced main and rod
bearing outflows (which goes as the cube of the clearance and
inversely as the viscosity) is also a reason there isn't much spray
inside a cold crankcase. All of these factors work against you,
especially on a new or fresh majored engine having minimum clearances.

Multi vis oils certainly help. Conversely having a summer weight oil
greatly increases the need for thorough preheating.

I use 32 degrees as a cutoff with 15W50, higher if it has been sitting
for more than a week. Below that I get an oil pump cavitation whine
on initial start on an O-320 E2D.

With minimum allowable bearing clearances, some engines have ZERO
clearance at about -10 degrees F. Cylinder choke and rapid heating of
the piston on cold start may also lead to piston scuffing. See
www.tcmlink.com for Continental's recommendations.

wrote:
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.


The differential expansion of aluminum vs steel is 6 microinches per
inch per degree F. Minimum bearing clearance is about .002 inch which
would take roughly 140 degrees of chilling to fully close up.
Probably even greater temps are needed for the cylinders to close up.
It is certainly a significant factor, but the reduced main and rod
bearing outflows (which goes as the cube of the clearance and
inversely as the viscosity) is also a reason there isn't much spray
inside a cold crankcase. All of these factors work against you,
especially on a new or fresh majored engine having minimum clearances.

Multi vis oils certainly help. Conversely having a summer weight oil
greatly increases the need for thorough preheating.

I use 32 degrees as a cutoff with 15W50, higher if it has been sitting
for more than a week. Below that I get an oil pump cavitation whine
on initial start on an O-320 E2D.