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15w-40 vs 25w-40 in hot climates


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MalibuRon

I have a 2014 wakesetter 21vlx w/monsoon 350SS engine with 130 hours on it.

I went to the local marine shop to buy supplies for an oil change.  They recommended the sierra 25w-40 vs the 15w-40, that Malibu recommends, due to the hot climate here in Arizona.

I read somewhere that the 25w-40 is also better to improve wear protection and increase catalyst life in newer inboards using catalytic converters..

 

Any insite on this?  


Any downside for running the 25w-40?

 

Edited by MalibuRon
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It shouldn't make much of a difference and I call BS on any impact to the cats, that said I'd consider the 25 if I didn't live in WI and never ran the boat on a cold morning

Edited by MustGoFast
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MalibuRon
Posted (edited)
2 hours ago, oldjeep said:

Let me ask this.  Does your engine temp run higher than the engine temp of someone in MN?  Or does your temp stay around 200-220?

Good point.


Perhaps then it’s more related to start up temps..? It’s 10:15 pm right now here in Arizona, and it’s still 97* outside, and around 110* during the day, so no cooling down.

Edited by MalibuRon
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MalibuRon
1 hour ago, MustGoFast said:

It shouldn't make much of a difference and I call BS on any impact to the cats, that said I'd consider the 25 if I didn't live in WI and never ran the boat on a cold morning

Thanks.. maybe it’s just brand specific with the synthetic additives they use?  
 

Here’s the article/ advertisement I came across…

 https://www.lucasoil.com/product/4-stroke-marine-engine-oil-sae-25w-40/#

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I read it, just don't believe it.  Your moto oil shouldn't be burning nor effecting temps in the cat so not sure how they can claim any impact on them.  I'm sure there's a way, but I'm not a believer with a fair amount of engine experience.  I'm sure it's not a problem jist find that marketing claim a bit bogus.

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MalibuNation

I can only add a little to this.  My 2003 came with 15w40 and contacted Indmar and they said 15w50 Mobil 1 was fine and wouldn't void my warranty.

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MalibuRon
Posted (edited)
6 hours ago, MalibuNation said:

I can only add a little to this.  My 2003 came with 15w40 and contacted Indmar and they said 15w50 Mobil 1 was fine and wouldn't void my warranty.

I found this article that was helpful for me to understand oil viscosity and it’s intentional design usage and ratings. https://www.castrol.com/en_us/united-states/home/learn/car-maintenance/oil-viscosity-explained.html
 

From what I gather after reading this, Indmar designed this motor to be regulated to run at a certain temperature range, and requires 40 grade oil viscosity to lubricate the engine’s metal parts at that temperature range, because of the size of the engine’s pathways that protect and clean those metal parts or surfaces.
 

Going with higher viscosity number like 50 will increase resistance and increase fuel consumption but will yield higher protection between metal surfaces.  But, too much resistance is not good and can cause over pressure problems.
 

Going the other way to a lower grade number like 20, will have a lower viscosity and provide less resistance than the recommended 40 grade at normal engine operating temperatures, which also provides less protection between metal surfaces.  So, too little resistance is not good and can cause overheating and wear damage to metal pathways.

 

As far as my original question to the 15w-40 vs 25w-40.. this article helped me understand that “W” stands for winter and the number in front is for starting engines with less resistance in those cold temperatures.  It’s what makes it a “multi grade oil” that has the ability to allow the oil to have a lower viscosity in cold temperature weather (winter) for starting the engine, and then run at the normal grade viscosity of 40 at the normal regulated engine temperature.

So 25w-40 in a hot climate does make sense as far as having a little higher viscosity on starts for protecting the metal surfaces without the need to be thinner viscosity for the cold weather starts.  The engine still runs in the normal operating temperature range with the recommended 40 grade oil viscosity providing the correct amount of engine protection at those temperatures.  

 

 

Edited by MalibuRon
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@MalibuRon - Just an FYI, the basic engine is a GM design, pretty much a crate engine with marine capability (anti corrosion and spark contained components).  The marinizer (Indmar, Mercruiser, etc) add their ancillaries and tune.  

As for the Lucas ‘selling points’, the cats do see all the engine blow by so there could be some oil formulation that plays nicer with them.  Hard to say as they don’t provide any real details other than 25 wt v 15 wt on startup as a difference.  For a boat, a straight weight oil would work fine unless you really do use your drysuit:-)

Edited by Woodski
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