5w- 30 vs straight 30

[wakeup 19]

I just did my oil change and shortly after I realized I put in 5w-30 instead of straight 30 Castrol. Will this cause any problems w/ my 350 gas mercs? I was told it should not but wanted to get some opinions. thanks rf:smt100

 

[gerryb]

Wrong oil for your engine. It would be OK if you only were puttering along at 10MPH all season long, but get the RPMs up and that oil will cause problems -- too much heat and stress on the metals. You engine probably won't blow-up this season but it taking years off the life of the engine. I'd change it.

 

[wakeup 19]

thanks guy's I will get it out this weekend.

 

[Jeffhort]

Well the thicker oil will give the engine parts more cushion. The thinner oil will get into the close Tolerances faster for start up wear. There is a balance that you should be concerned with. Most engine wear is caused by start up. When oil is not where it should be. I think the 20/50 is a much better match than a straight 30W or even a 10/40. Let me explain it all comes down to heat and oil break down. That is where the wear comes in. Heat is caused by Friction and friction equals wear. The temp caused by friction is where oil breaks down. So to answer you question here is how it works in a multi Viscosity oil. Your 5/30 oil is a 5 weight oil that will stand up to the same temps caused by friction as a 30 wt oil, hence the 5w/30w. A 20/50 oil is a 20 weight that will get into those areas faster than a 50w oil. but will not break down until it reaches a temp where a 50W will break down. I would run a 20/50 for my boat just my preference. Now you have heard it is bad to change brands and viscosity of oil. Well that was when we had detergent oils and non detergent oil. If you ran non or a lower detergent oil then changed to a higher detergent oil. The detergents can cause extra sludge build up to loosen up and plug up your oil galleys and small holes. and starve your engine for oil. In these days most oils have good detergents. Don't use diesel oil it is real high detergent because diesel is dirty. But I believe you could if the engine started with this oil. But I'm not sure about this. Good boating guys

 

[tdappleman]

With a 5w30 oil - you're at a 5 weight oil for startups and until the oil temps get to approx 180* which doesn't take long. After it reaches normal temps it behaves as a regular 30 weight oil. Think of the 'w' as 'winter' as in cold. The advantage as Jeff stated is it allows for faster oil circulation on startup and given your climate you may still have cool weather which will affect your oil. I personally would leave it in since most engine wear occurs at startup but to each their own and you need to feel comfortable with your decision.

 

[dpmulvey]

I'm sorry, but I have to disagree with you 100% on this one. The engine manual from mercruiser is very specific in this case. It says, and I quote "IMPORTANT: The use of non-detergent oils, MULTI-VISCOSITY oils (other than Quicksilver 25W40 or a good quality 20W40 or 20W50), synthetic oils, or other oils that contain solid additives are SPECIFICALLY not recomended.

I would not use the 5w30 because it is not heavy enough of oil, and it is not recomended by mercruiser. Granted this manual I am reading from has not been updated since June of 2003, but the new manuals have only been changed to add the semi-synthetic and synthetic mercury spec oils. I don't care that the oils are made by mercury, and they are only trying to make a buck, they know their engines and they know what it takes to make them last.

Doesn't a lot depend on what the manual says for the OP's engine?

 

[dpmulvey]

That is out of a manual that covers his engine. I have an extensive library, basically because of the 12 previous boats I have owned.

Fair enough. So if I understand you correctly, he needs to dump the 30 weight altogether?