Ok to use automotive motor oil in 15 hp lawn tractor – topic tropico 5 power plant

Reductions in Zinc content of motor oil came about as catalytic converters were being damaged by it. Also, roller tappet camshafts started being used to reduce internal friction between the camshaft and the tappet. So, between the two reasons, oils were reformulated to take advantage of less internal friction and to lessen cat damage.

This started being an issue in the late 1990’s for older cars. Camshaft wear many times was not noticed, just a factor in the car "wearing out". When it came to be a topic of discussion was for the antique and hot rodders. At that time it was said to use a Diesel rated oil, more anti-scuff and anti-wear materials in that instead of gasoline rated oils.

Comp Cams, as many of you know is a manufacturer of performance parts. They were having many warranty claims for flat camshafts. While engines can be retrofitted for roller tappets, many prefer to use flat tappets for many reasons. Well, Comp Cams warrantied these but started investigating as they thought it was a bad batch of camshaft blanks.

Further studies and oil testing found that the new oils were lacking more than the older versions of anti friction additives. Hence some oil marketers stepped up with oils being designed for the "vintage" cars. Some make "pour in" additives, choice of the user. In the two cars I have with flat tappet camshafts, a ’71 (engine anyways) and a ’67, they both get Valvoline VR-1. That is a high zinc oil.

Harley Davidson for one recommends the use of their own brand oil (surprise) but also stated in owners manuals that Diesel oil can be added in an emergency as it closely mimics the additives that they require. That was a few years ago, I have not looked in a newer owner’s manual to see what their take is presently.

Just my opinion, not an engineer, but I would (and do) use a power equipment rated motor oil in my JD X300, my snowblower and my Coleman generator. The Deere is nine years old, the Craftsman snowblower is fourteen and the generator is fifteen years old. It may be a couple bucks more expensive per quart but still cheaper than a rebuild.

Most small engines without a pressurized oil system have a pin running off of the connecting rod or cam gear designed to splash or throw oil throughout the crankcase, the camshaft, and cylinder bore. These parts don’t get oil until adequately sprayed after the engine has started running at full speed. The oil for these engines would (hopefully) have a higher residual quality and engine specific additives (I think that reflex/deflex 64 and shovelhead explained this better than I could have) for small engine use. Another consideration would be that the engine is air cooled and may have hot spots in the crankcase that hopefully are cooled somewhat by the oil bath. This type of oil would be designed with these things in consideration.

A pressurized oil system would start pumping oil as the engine is being started. Most of the engines now will not energize the coils of the ignition system before optimal oil pressure has been obtained. Automotive oils would work better in a pressurized system because that is what they are designed for. Plus the emissions aspect and fuel economy restrictions.

Where do you live, what engine are we talking about, how long does the engine run before you shut it off, and I can provide better recommendation. I have changed oil thousands and thousands of times in small engines. I used to have a small engine shop, and noticed some trends over the years. What works, what is adequate, and what doesn’t work.

I will also add that boutique synthetic oil at $10 a quart or more is an outlandish waste of money. I’m always on the lookout for an oil bargain, and I almost always get my oil for 50 cents to $1.50/quart, to include high dollar synthetic and fleet/diesel oil.

15.5 hp Briggs, has an external oil filter that I change annually, so it must have a pressurized oil system. Air cooled, Husqvarna model with a belt driven 38 inch deck with two blades. I live in SE Va, so summers can get very hot and humid. Not has hot and humid as New Orleans or Easely SC, but plenty hot enough. When I turn off the engine it stops immediately normally. But I rember one summer when it would deisel-run after I shut off the ignition. I don’t know why it did that, nor has the problem returned, but it may have been exceptionally hot weather when it happened, I don’t recall.

There is one thing that happened once, that I haven’t mentioned, since it may not relate to what we’re talking about. One summer I hired a mobile power equipment dude to do an everything maintenance job, and later discovered he didn’t put enough oil in it. So when I ran it on a hot day, I noticed the engine was blowing lots of smoke, so I shut it off immediately and checked the oil. Sure enough that fellow failed to fill it with sufficient oil. That was the last time I hired a mobile tech. I never thought he would have done that because he came highly recommended and worked at Sunbelt Rental and maintained all the machines. The engine has never been the same since, so there has been some damage, but seems to runk OK as long as I keep the oil topped off, since it does burn some oil since that incident.