[moondance100]

What kind of engine oil do you guys run in your engines? I'm running 9 qts of 15w50 Mobil one in my 502....might be a little overkill, but it's a lot cheaper than the engine!

[frankendebb]

Is there any truth to the theory you should use the same engine oil everytime (ie; brand and viscosity) ?

I've been told changing oil brands and type screws with the seals and stuff due to the different addatives and so forth.

urban legend or fact ?

[mikeyt]

'Tis urban legend as far as i'm concerned. The only thing that i believe might pose a problem is switching back & forth between types of oils (synthetic, semi-synthetic & dinosaur).

Perhaps we should let "Dudders" weigh in on this one. He has a background in this sort of stuff.

[dudders]

I agree, it is a bit of an urban legend. However - sticking with the same manufacturer is always a good idea. You are right with the additive thing, some put a little bit more VI (viscosity index) improver in some than others, some put a bit more detergent etc etc. Sticking with the CORRECT viscosity is the MOST important though. And of course I have mentioned in other threads stay with a well known company.
A small company asked us to make a range of oils for them, giving us their design specs for various oils - it met the API requirements (Just), and man, there would be no way I would put thier crap in my lawn mower let alone car or boat! They were flashy and plenty of advertising for a while but somewhere down the track they will be getting plenty of claims brought upon them.
So stay with the big players for christ sake.
Using synthetic engine oils is over the top simply because the engines will not benefit from it at all - unless you are WOT all the time.
BUT drive synthetic oils ARE a good idea. You will need to completely flush your old oil out though (a tiny bit left is ok).
I think Mobil - Shell - perhaps Valvoline all make synthetic gearbox / drive oils.
The difference being is the tolerence the synthetics offer. Any excessive heat, or absorption of alien products will not deminish the oil as quickly as mineral based oils. Of course the oil will last twice or three times longer than Mineral oils as well.
This is the same with engine oils of course, so you will just have to weigh up costs.
cheers
Tony

[Jeff Barnett]

I beg to differ on this. First off I have no connection with Mobil Oil, however Mobil One Synthetic, is the best oil an engine can have. I've done independent studies, with long term use, granted, these test were not marine application, but street, race track and long distance highway driving, at constant speeds. First off, once you go synthetic, you cannot go back. You should also never use synthetic until the engine is well broken in. In a car it's recommended at 6,000 miles. If you try and break an engine in on synthetic, the rings will not seal, yes it's that slippery. It's also not for use in pre 80's engines, as in small and BB Chevy’s from the 60's and 70's, they will develop oil leaks within 200 miles of use, crazy huh?Dino oil is just that, old dead Dinosaurs, that decomposed into crude oil, they leave deposits, and gunk on the internals after about 30,000 miles. Synthetic, has none of this, and maintains its viscosity far better than Dino oil. As for using 15w 50, that’s a bit heavy, does your engine pull good revs? It’s also a nice load on the crankshaft. 15w 30 is whats used in Corvette racing engines, they run Hi revs for a long long time. However if you are in a very, very warm region, and it works for you, it won't hurt other than higher oil psi, and slower revving.
I swear by it, having been using it for over 15 years, in all vehicles, and in car applications, I change it every 6,000 miles.

[moondance100]

wow...thats interesting.....I've been running Mobil one since day one in my new 502 and it's been using some oil...if that stuff is so slick the rings won't seat, that explains a lot...so what do I do now? Change it to dino oil for 20 hours or so and then back to Mobil One???

[Jeff Barnett]

Not really sure what to tell on that one. I know dino oil and synth. don't mix. perhaps some sort of detergent engine wash by STP or something. The problem and benifit from synthetic is you get zero scuffing on engine parts, bearing surfaces look new after 30K miles, however, with piston rings, you want a little scuffing for a few hundred miles, at least. Race engines are run on Dino oil for about the equiv. of 200 miles, then switched out to Mobil One. I'm willing to bet the reason you're using oil is due to that.

[dudders]

Do not mix synthetic with Mineral based oils at all, as I have suggested in another post.
I am no mechanic so I cannot tell you about the run in period of motors and what the synthetics will do on this particular motor during the run in period - however the mercruiser handbook does suggest not to exceed certain speeds and revs for the first 30 hours or so of the engines life.
Best to check with Mercruiser on that one. I have contacted them about a couple of questions I had via their website and received a response from one of the techs quite quickly.
As far as 15w/50 engine oils are concerned this is not too heavy for moderate to warm climates - 15w/30 engine oils are also fine, just keep an eye on your oil pressure whichever you use. And as I have always said - try and stick with the manufacturers recommendation of the viscosity.
If you like synthetics go for it - just make sure you flush your engine first.
If you have been running mineral based oils for years - changing to synthetic is not going to benefit you greatly.
Regular engine oil changes is the key to keeping your engine running longer with less mechanical problems.
My car runs a performance enhance motor (225kw - 300hp) and I give it a pretty good flogging, it has done over 160,000kms (100,000 miles) and the motor looks as good as the day it was made simply because I change the oil and filter regularly (around 5000 miles).
Just my 2 cents worth

[magandy]

Has anyone ever used Amsoil? They make outstanding oil and filter products and have been around longer than Mobil or any of the major brands.
I use it in my cars and absolutely love it!

Andy

[mikeyt]

Originally Posted by magandy

Has anyone ever used Amsoil? They make outstanding oil and filter products and have been around longer than Mobil or any of the major brands.
I use it in my cars and absolutely love it!

Andy

hi Andy

One of the other boating boards (which shall remain nameless here) discussed the use of Amsoil and it was generally agreed that it was good stuff so you should have no problem using it in your boat. Just follow Dudders advice below....