Winter Oil? Do you guys switch to a "Lighter" Oil in the winter?

[Bill Greenwood]

Ryan, I don't see the logic. How does cold weather make the clearances of a bearing which are in thousands of an inch get smaller? The crankshaft doesn't expand when its cold, the bearing shell doesn't expand either. If the metal changes any it would shrink when cold.

 

[Mtns2Skies]

Ryan, I don't see the logic. How does cold weather make the clearances of a bearing which are in thousands of an inch get smaller? The crankshaft doesn't expand when its cold, the bearing shell doesn't expand either. If the metal changes any it would shrink when cold.

Dissimilar metals expand and contract at different rates.

 

[Bill Greenwood]

Mtns. your statement as far as it goes is true, but not the situation Ryan described. If its 0* weather overnight, the engine parts haven't expanded at all, they shrink in cold weather.

 

[Capt. Geoffrey Thorpe]

The colder the temp is, the smaller the clearance between the bearing shells and the crankshaft are.

Mtns. your statement as far as it goes is true, but not the situation Ryan described. If its 0* weather overnight, the engine parts haven't expanded at all, they shrink in cold weather.

The crank is iron/steel. The case and bearing caps around the crank are aluminum. When it gets cold, the aluminum shrinks more than the steel which reduces the clearance.

 

[Dan Thomas]

The crank is iron/steel. The case and bearing caps around the crank are aluminum. When it gets cold, the aluminum shrinks more than the steel which reduces the clearance.

This is true, but the bearing shell is steel and the ends of the bearing shells are butted against each other under pressure from the case. Without that bit of clamping, the shells would move and fret the case and everything would come loose. In the cold, that case is more likely to spread apart a tiny bit at the bearing saddles. I would expect very little change in bearing clearances. The much bigger factor is the resistance of cold oil to flow and be forced into tight places like bearing clearances.

The piston is a high-silicon aluminum and has steel struts cast into it to control expansion from heat, but it still has a larger coefficient of linear thermal expansion than the cylinder, which is steel. In the cold the piston-to-cylinder clearances are larger, the reason for more blowby when cold and the large amounts of water vapor (from combustion) that gets into the crankcase and causes corrosion.

The bearings need oil much more than the piston and cylinder. A constant flow of oil is needed into the crankshaft in order that the bearings stay wet with it. The pistons get their lubrication by oil thrown off the crank journals as they rotate. The piston and rings need only the thinnest film of oil to stay happy, and, in fact, if the bearing clearances are too large (from wear or poor overhaul) the cylinders will get far too much oil, flooding the cylinder walls and causing the rings to hydroplane and letting oil into the combustion chamber. The engine then uses lots of oil and the plugs foul up quickly.

Run an engine out of oil and it's those bearings that will fail first every time.

 

[RyanB]

Ryan, I don't see the logic. How does cold weather make the clearances of a bearing which are in thousands of an inch get smaller? The crankshaft doesn't expand when its cold, the bearing shell doesn't expand either. If the metal changes any it would shrink when cold.

If its 0* weather overnight, the engine parts haven't expanded at all, they shrink in cold weather.

Did you read what I wrote at all? Because that’s exactly what I said. Engine pre-heating assists with metal expansion from parts being compressed (shrinking) in cold temps.

 

[chemgeek]

Multiweight year round. Keep it simple.