Which oil to use?

[popeyefoghorn]

Hi, I have a '78 Chris Craft with a 305 Marine Power inboard. What type of oil would be best to use? Full synthetic 10w-30, or non-synthetic strait 30. Any comments would be appreciated, the guy I bought it from did't know what type was in it. Thanks.

 

[horndog]

Re: Which oil to use?

straight 30 is what is recommended. if you can find synthetic in that weight go for it. Did he do the maintenance or did he have someone else do it?

 

[2770]

Re: Which oil to use?

I have an older v8 as well and when new sae 30 is called for .I use sae 40 now .The older the motor the thicker the oil.The temperature that you operate in will help dictate how heavy to go. CC

 

[akriverrat]

Re: Which oil to use?

if you put synthetic in an older motor any minor oil leaks will get much bigger and crank and valve seals may start leaking. if the engine is using oil it will start using much more. switching back to regular oil may not help if seals start leaking. this is why it is not recomended to switch to synthetic in high hour engines. i put it mine after 300 hours or so and oil consumption tripled. even with fresh rebuilt heads.

 

[popeyefoghorn]

Re: Which oil to use?

Thanks for the suggestions, guys. The old owner had someone else do the maintainance and he did't know what they were using for oil. I'm still investigating. When you say you use 40 is that 15w40 or just stait 40? If it is strait 40 isn't that hard on the engine at start up?

 

[Boatist]

Re: Which oil to use?

I ask this same question of the factory rep for my engine several times. The answer always straight 30 weight. I ask why can't I use use 10W-30, answer was marine engines offten run at or near full throttle and the multi oil break down faster. I ask same again after all the new Synthetics came out and got the same answer. They have nothing against Synthetic if it is straight 30. I am still think about useing Synethetic as rare for my to run engine over 3000 rpms.<br /> Only time I would ever use 40 weight would be if only way I could get oil pressure and motor was ready for a complete rebuild, or leaked oil so bad it was the only way to keep oil in it. Motor only runs 150-170 degrees not 200 like a car. If the motor is that bad time to fix it.

 

[popeyefoghorn]

Re: Which oil to use?

I found a synthetic strait 30, it is put out by Volvo-Penta, needless to say its an arm and a leg. It must be available under another name, has anybody seen this? Where can you buy it?