If they were mine, I wouldn't run any kind of flush. Just refill with synthetic oil at the next change.

I have run 10W-30 Mobil 1 in my all 4-cycle OPE for years. If you are interested in sticking with 30W, I believe Briggs & Stratton markets a synthetic 30W oil.

I'd just put Syn 10-30 in the both of them.Syn and Dino oils are ususlly compatiable.I have not seen any Straight Wt 30 Wt syn,only multi wts.JMHO tbk

There are a couple/ synthetic oils that are listed as 30/10W-30.

A synthetic is, somewhat by its nature, close to a straight weight oil.

Think of water- It's pretty much the same viscosity at 33-211 degrees. (I avoided 32 & 212 so we don't get into latent heat issues):-)

"There are a couple/ synthetic oils that are listed as 30/10W-30."

Bill, please tell us the brands. Thanks in advance.

-Deerslayer

Deerslayer, if your serious, it is amsoil (I think there are 2 types), but I suspect you knew that, but maybe my reading of your post is off.

Optsyeagle, any particular reason for switching? I'm not in one camp or the other, just curious.

I, like many others I am sure, cut my grass on some pretty hot days in the summer (+32C). I just figured that synthetic oil would protect my motors a little more on those days since they are both just air cooled. Synthetic oil is a lot more slippier and since I only change the oil about once per year, on these motors, I figure the cost difference is not really a factor and lets face it; the main reason we put oil in is to make things very slipery (I am sure the experts have come up with a more technical term for this).

That is my thinking.

Run Dino oil, HD30 only in the Tecumseh please.

Lubricity of synthetic is a property that is probably better than conventional oil, but I understand it really only comes into play at the extremes of temperature. At any temperature I'm likely to be cutting grass I suspect either lubricates equally. The 2 properties of synthetic that interest me for OPE are shear stability and cling. My equipment may sit for weeks or months not being used and then gets a cold start, which in any engine is where the most wear occurs. I would think the synthetic ability to cling to parts better would give me more protection under that circumstance than a conventional oil. Synthetic does not shear as much as a conventional so I'm pretty sure that if the engine needs a 30wt that by the end of the day I'm not running 15 or 20wt because it has sheared down. I'm not clear on the time it takes for an oil to shear or whether there is any elasticity in the viscosity, meaning when the oil cools does it regain its viscosity somewhat or once sheared, that's it. There seems to be a lot of support for HDEO (diesel oils) in air cooled OPE. I'm currently running 15W40 Rotella in my new Kawasaki engine and I can detect no difference in engine operation from the factory oil. I'll run it till 25 hours or seasonal change and then decide whether to stay or go to a 5w-40 synthetic in that engine. Of course, I suspect that a straight 30w would work just as well and I could use one oil for all the small engines. If Rotella T Synthetic weren't so expensive I'd be tempted to use it in everything I own, cars included.

I agree with most of soccer_dad's comments except about the high "cling" factor of synthetics. My understanding is that this is one attribute where syn's are deficient compared to dino's. This was a big topic in the private pilot world, where many apparently found that leaving synthetic in their airplane engines over winter lay-up's allowed significantly more internal corrosion in areas such as piston's, due to teh propensity for teh oil to drain off the parts. This is also a current theory with hobby car owners. Overall, the consensus that I see is that if you are going to use the motor periodically, then leave synthetic in through winter in order to benefit from all of teh other features such as rapid flow and better cold start protection, but if you lay-up, change back to dino while it sits.

"has used regular 10w30 oil in it since new."
"I, like many others I am sure, cut my grass on some pretty hot days "

All B&S engines I am aware of, recommend straight SAE 30 weight oil above 40 degrees.

"I only change the oil about once per year,"

All small engines owners manuals that I have seen recommend the same change interval for dino and sym oil.

Walt Conner

"All B&S engines I am aware of, recommend straight SAE 30 weight oil above 40 degrees."

The Intek V-Twin Operating and Maintenance Manual for the 400000 and 440000 series engines states that synthetic 5W-30 and 10W-30 oils may be used above 40 degrees F.

The manual also states that the same oil change interval should by used for synthetic oils, as you indicated.

Soccer_Dad, thanks for the info.

-Deerslayer

Now since the discussion moved towards, how well one oil adheres to the engine components compared to the other, in order to give rust protection. It brings up the question of whether these lawn tractors and mowers should have fogging oil sprayed into them before winter storage.

Do you guys fog your motors?

In regards to synthetic's ability to cling....
When I went from regular oil to synth, and only with Synth that I noticed this:

check the dipstick next day/cold engine/etc prior to start the engine, the oil level appears way over full, like 2" higher than the max! wipe the dipstick, re check oil level and it is normal.
I believe this is a good ability "Cling", actually more like creep up.

I do not recall seeing this with regular oils (maybe? Has anyone else noticed this too?)

mbsl98, if you have some links I'd like to read some more. I may be misinformed on the cling, just thought I remembered when Mobil 1 first came out that was part of the advertising on how well synthetic oils would cling to engine parts. I'm pretty sure ester based synthetics are polar and cling better than PAO based, but beyond that simple fact I'd lose any debate on what the real differences are between the 2.

I've never fogged an engine. If I thought it was going to sit that long I'd probably sell it. A few months at a time shouldn't be a problem and any corrosion should go right on out the exhaust pipe. I'd consider care of the fuel system more important, especially with today's ethanol blends.

I use synthetic oil in all my vehicles & riding mower. The lawnmower, pressure washer I just use 30 weight. I have added synthetic to top them off on occasion.
The synthethic oil can go much longer between changes if it is filtered. I do it once a year on my tractor even though the hours run are a bit past what the manual recommends. In cars it can go 12K with no problems. I change them twice a year whether they need it or not.
I do fog all my engines when I put them up. It's easy & cheap insurance that the internals don't rust up over time. Valves stems can be susceptable to rusting. It's a habit I got into with outboards, even though I realize they usually sit longer in storage.

You want to check out BITOG for more then you care to know about oils and their properties. Lots of facts and lots of opinions.

-gh

Here is a link that might be useful: bitog

I am not sure I would reccomend switching to synth for the sole reason of longer between oil changes. And IMHO people that leave any oil in any engine for a year, or 12K miles is asking for trouble.

The oil may still be able to lube the engine, and do all the slippery stuff that an oil is to do but everyone forgets about contamination. Be it from metals that wear in an engine or just plane dirt and everything inbetween.
In most cases we are only talking a quart or two for these little engines. These hard working in most cases un-filtered little engines.

Change your oil folks, oil has changed to make it more fuel efficent and less friendly to your engine.

http://www.pratherracing.com/oilwoes.shtml

There is also a link on this page to other oil info.
Bottom line is that oils have changed, and while mowers are not high rev race engines they do work very hard in very harsh enviroments. It is still applicable.

I switched from Castrol conventional 10W-30 to Mobil 1 Synthetic 10W-30 when my 18hp Kawasaki twin air cooled engine had about 60 hours on it. The owners manual recommends changing the oil and filter every 100 hrs or once a year. I put on about 50 to 60 hrs a year. I change it in the fall when I put it away for the season. My oil level does not change at all in the 60hrs of use. It may get a little darker, but not black. I make sure my air filter is always clean. So far, I have had good luck with the Mobil 1 oil. I chose to go with synthetic oil because there are several days when I have to mow in temperatures above 90 degrees F. I just think the synthetic oil gives a little more protection on these hot days. Charles Ranheim

I agree Charles, the oil in my Deere barely looks dirty after a season of cutting & it's 15 years old. Mobil 1 is what I use too. I've never had to add oil either.
As far as cars go, why not get the most out of the synthetic. It isn't conventional oil. I use good filters, not the cheapest(fram).

Deere says you can double the change interval with a JD engine and JD synthetic. I didn't see any exclusion of yard tractors.

Royal Purple has straight weight synthetic.

I use Castrol syn-tec in all my air cooled motors, these little motors don't hold much oil so I really can't see cost even being a factor. Down here temps in the 90's are normal, a lot in the upper 90's, so I want to give those hard working little motors all the help I can. I still change oil at the recommended 25 hrs too. My ole 1855MF with a B48 Onan has over 2500hrs on it and still runs and sounds like it's suppose to, the K341 Kohler in my mowing tractor still runs and sounds good, it's a 1972. Works for me so I'm sticking with the synthetic oil.

o.k-one thing might not have fo do with another but, I own a 1600 Vulcan Nomad (Kawasaki) motorctcle..being it is a kaw-I use motorcucle oil of course for the fact that regualar car oil can ruin the clutch...has anyone asked if the synthetic oil that everyone seems to be using can effect the clutch? and if not then mobile one does make a zero/thirty full synthetic oil which when cold will crank up quicker and lubricate much faster thus avoiding any problems from an engine that might be sitting for more than one week...also oil should be changed every 3000 miles for vehicles, and motorcycles or six months, which ever comes first...on my X304 I changed the oil at seven hrs and will continue to do so...as far as synthetic in a lawn tractor this is new to me so I have not used it yet..but one more word of wisdom, once you use synthetic you cannot go back to regular oil, nor can you mix them as this will do more damage than good...now I will wait to hear all the experts, such as myself reply to this one, but be kind as I am old and fragil..lol

Only oil that is designated as "energy conserving" is bad for wet clutches like the kind found in motorcycles (and ATVs). Most lawn tractors do not use these types of transmissions or clutches. And the bit about switching from synthetic to dino oil and back is an old wive's tale. You can indeed switch from one to the other if you wish, and you can even mix the two without harm.

Not true that if you use synthetic oil you can't go back to standard oil. Why would you want to? Their are a number of semi-synthetic oils out there. The same as mixing oil.
The only thing I've heard not to do is to switch over to synthetic after high milage, say 100 k miles in cars, as the synthetic may loosen sludge that could clog things up.

For years Toyota used to say on their Customer Care Website: You can use synthetic oil, but if you do, you should not switch back to conventional oil. I challenged this many times, and they stuck with their statement, but would not say why. I then noticed this statement about synthetic oil went away. I sent another question about using synthetic oil and going back to conventional oil. Now, they say there is no problem switching from synthetic oil back to conventional oil. I also noticed my Toyota Dealer now carries it as an optional oil to use.

Charles Ranhiem

I use what oil the manufacturer of the engine recommends, if synthetic oil is better then why doesn't the manufacture of the synthetic oil add a extension factor on the engine warranty? If efficency is the factor why isn't a warranty added for increased efficency? I have never received a answer on this except (trust me). Over my life experiences those 2 words (without facts) get me in trouble. What has been your experiences?

why should a car manufacturer extend a warranty based on the type of oil used? It's not in his interest & how could it be proven. A number of new cars do come with synthetic oil. I believe Corvettes are one & some German cars.
Toyota had a problem with sludge build up based on the recommended oil change interval. Synthetic oil prevented the problem, which some consider a design defect. By saying not to switch back, problem solved.

"if synthetic oil is better then why doesn't the manufacture of the synthetic oil add a extension factor on the engine warranty? If efficency is the factor why isn't a warranty added for increased efficency?"

I am not aware of any company that extends the warranty of another company's product based on the performance of their product.

Edsacre is correct regarding some new cars coming with synthetic oil. Both Mobil and Castrol state that new engines can use synthetic oil immediately.

New Car Oil

Outdated information dies slowly partly because it gets propagated in forums after it is no longer valid.

-Deerslayer