Synthetic Oils?

I was wondering if any has coverted to synthetic oil in an older Nautique? Is this a good idea? What are the pros and cons of this convertion? -Brad-

If you use synthetic in an engine after using regular oil, it can develop leaks.

Brad:

79nautique got it right...many different opinions...here's mine. Go ahead and make the switch and if what Tim D says happens, then you can switch back again. The leaking issue is caused by seals shrinking a bit with the use of synthetics. So, marginal seals may start leaking. If you go back to dino oil, the seals will swell again and the leak will stop.

I think the spun bearing thing is just coincidental or a very rare occurance.

With all that said, I have nothing against dino oil when changed yearly at the least or more often depending on the use of the boat.

Syn oil is overall thinner thus the oils leaks and you get spun bearings. Or maybe a better term would be the surface tension is less i.e. small diameter droplets. Making it easier to pass throught smaller gaps in oil seals thus your leak and with the Syn improved properties it holds on long and takes a lot longer to burn off thus the smoking car even though you replace with Dino oil.

David F   "I think the spun bearing thing is just coincidental or a very rare occurance."

It is no fluk or rare occurance and will happen every time. Syn Oil cannot fill the gap in worn or loose fitting bearings. Racing engine bearing clearances are by far much greater than what you will find in a automotive engine when both are brand new. For instance a new LT1 crate motor will have clearance from say .0005" to maybe .002" where a race engine or even a 50K mile engine are more like .003"-.005" and syn oil cannot fill this gap and you will spin the bearings. Maybe you have 40K to burn. But if I buy a new motor and expect it to run for the year in race conditions and then your first week-end out and you make two runs and the motor is junk becuase of a spun bearing. You look in to why and the person that made it looks into why and it is clearly oil failure you will change your mind. It's not like these guy are shade tree mechanics like a lot of you, these are proffesionall engine builders that have multi-milion dollar deals riding on how will there engines perform.


Brad my advise to you is

if Dave wants to buy you a new motor when yours puks for using Syn oil go a head and use Syn oil. Otherwise stick with the cheap dino stuff.

I think I will stick to dino. Thanks for all your help on this matter. -Brad-

79Nautique:

We are talking about marine engines here (nor racing engines). I admit, I have no experience with racing engines. Now, I use synthetic oil in ALL my engines, including my '77 Martinique (351W) and have been for years. None of my engines burn oil. The boat engine leaks a bit of oil at the rear main seal, but did with Dino as well. Here are list of vehicles I have used synthetic oil in over the years:

'88 BMW 750iL *
'98 BMW 740iL *
'02 Suburban *
'77 CC Martinique *
'71 Chevy Camaro (with 370hp LT1 engine that I built).
'87 Jeep Cherokee
'80 BMW 633CSi *

* means I still have the vehicle with NO problems. So, my real world experience says synthetics do NOT cause problems. I will say that if a new engine came with Dino, then Dino should be used until the rings have fully seated. Otherwise, the synthetic can prevent the rings from wearing in properly and lead to excessive blow-by or oil consumption.

Like I said, I have nothing against Dino oil and it took me a long time to change from something I had been doing for many years.

Horsepower or mileage thinner is better. The new Hondas come with 5w 20 oil to help with mileage. The most friction happens during start up before oil is pumped to the top of the engine. Lucas oil helps oil stay attached to parts at the top. From my experience, I will stick to dino oil.

Dave

How many miles where on the engines when you started using Syn? I'm betting they where pretty new or freshly overhauled in all cases.

Lets pay three times has much and go twice as far not a lot of savings in the long run. And agin if it is a new engine or freshly re-built then ya you can get by using Syn. and not see a problem with nornmal driving. Put a heavy load or a constant load and things change quickly. A car engine is loaded only at take off and the faster you go the less power is required to maintain that speed. On a boat the load is always there and never decreaces thats why you'll never see a vacume advance dist. in a boat unless some dumb ass replaced the factory unit.

I tend to be rather anal about changing oil. I got that way due to my uncles farm where maintanance was job one. All of our equipment is greased daily (when used) and oil changed exactly as reccomended. WE use John Deere Torque Gard oil and have machinery that we bought new in the 60s and 70s that has now power loss or smoking. Some of these Deeres have 8000 and better hours! I wouldnt use a synthetic oil as it isnt reccomended by my owners manual. As previously mentioned the engineers and designers of this equipment arent shadetree mechanics either and as such I have to assume that they know a lot more than I do. Anecdotal evidence aside (my old tractor, boat, car, truck etc ran for 1,000,000 miles with synthetic or dino) The engineers and designers know a lot more than we do and I gotta go with the theory if its not in the book dont do it. Perhaps some new car manuals reccomend the use of synthetics but I still wont use them- I like to have fresh oil in my engine.

Thanks C.C.F. for all your help!! -Brad-

Well lets start with ambient temperatures in the operation of boat engines. The cold start problem in autos occurs @40 degree & lower ambient temps. The bearing material in marine engines is different than modern auto engines, more like heavy duty truck application.
I would not worry about cold starting as to high filming load on the bearings @normal operating rpm & temp. Marine engines are making horsepower(load) anytime the boat is under power and all the time the boat is under power. Auto engines load highly on acceleration by once you are up to speed, with 3,4, 5 speed transmission the engine horsepower to maintain speed are greatly reduced. The ratings on oil, ie sh,sl,etc pertain to chemical packages & properties relating to specific needs of auto engines. You will find that heavy duty truck(diesel) engine use different formulation that auto & light trucks. Check out the specs in these examples see what you find. Also the viscosity of multigrade oils are not related to oil thickness but the properties the certian weight oil perform.