40 weight oils in small engines?

Status
Not open for further replies.
Joined
Oct 9, 2007
Messages
931
Location
OR
I have a rather large collection of various B&S engines...many of them worn out but still chugging along just fine. I like to use 40 weight oils in the older ones, but I'm wondering why the Briggs factory recommendation has always been 30w? What is the disadvantage to a 40w oil? To me 40w makes more sense in an engine that runs at ~400 degrees and has very loose tolerences...am I wrong?
 
I've got an edger with a very old Briggs & Stratton on it. It developed either a rod knock or piston slap (I don't know which) and a gardener told me to change it over to SAE 40. That's the best thing that ever happened to that little engine; the noise is gone.
smile.gif
 
Air cooled engines run a lot hotter than auto engines.
Thicker oil can help a tired engine last a bit longer.
Seals a bit better. Straight weight 40 is hard to find
at mass marketers.
 
most of these air cooled flatheads only run 400F on the cylinder head, where there is no moving parts. the cylinders, blocks etc dont run nearly that hot.

also the smaller engines usually have aluminum bores, so theres a far greater thermal efficency compared to a sleeved iron cylinder. again reducing temps. besides the rings, and crankshaft and various bolts theres basically no steel or iron parts to these engines.

with that said, these little motors can still get pretty warm.
 
Yep I have always run Rotella T 15w-40 in all of our generators, mowers, and pressure washers. A lot quieter then using 30 weight oil. I would also recommend Delo 400 straight 40. If you have a hard time finding it check a marine center, they usually carry it.
 
Yesterday at Advance Auto Parts they had a bargain rack by the front door. I got 4 quarts of Rotella straight 30 weight for 99 cents a quart. It's destined to go into my lawn equipment, Koehler, Honda and Briggs this week when they get their annual service.
 
Originally Posted By: SecondMonkey
I have a rather large collection of various B&S engines...I like to use 40 weight oils in the older ones, but I'm wondering why the Briggs factory recommendation has always been 30w? What is the disadvantage to a 40w oil?

Most engines are designed to operate with SAE-30 oil as the best compromise between being able to start cold, circulate, and protect while at operating temperatures. Multi-grade oils improve the starting and circulation capability, but sacrifice some protection at operating temperatures.

That being said, most small engines are splash lubricated rather than pumped circulation. 10wt, 20wt, 30wt, 40wt in a splash system are all going to "circulate" the same since the oil's being thrown around by a dipper on the end of the connecting rod or crankshaft.

The thicker the oil, the better it's going to protect moving metal parts. So, there really is no disadvantage to using SAE-40 oil in your small engines other than a slight increase in fuel consumption to overcome the added viscosity drag in the bearings and between the piston and the cylinder. You'll never notice that difference.
 
Status
Not open for further replies.
Back
Top