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15w40 or synthetic 10w30 for 115°f temps #5135042 06/15/19 02:29 PM
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leroyd92 Offline OP
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I have 2 boats with 350 engines in them. I've always used 1540 or 2050 in them but I've been curious if I'd gain anything from a full synthetic 10w30.

Engine RPM never goes past 4k

We cruise them at 3k.

My only concern is certain spots of water can we warm especially late in the summer.

What are your thoughts?


My life became simple once I learned about diesel oil........
Re: 15w40 or synthetic 10w30 for 115°f temps [Re: leroyd92] #5135043 06/15/19 02:32 PM
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Lolvoguy Offline
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Originally Posted by leroyd92
What are your thoughts?

Why change what's working?
Only difference I could see, is additional cost to you.


06 Lexus IS350- Wife
88 BMW 325is- Mistress
Say "no" to Turbo!
Re: 15w40 or synthetic 10w30 for 115°f temps [Re: leroyd92] #5135061 06/15/19 02:53 PM
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Chris142 Offline
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The water can't be nearly as warm as the ambient air temp or the water coming out of the radiator.


02 Wrangler Napa high milage 10w40
87 F250 Valvoline 15w40
07 fjcruiser Car lube plus 10w30
Z400 castrol T 10w40
Can am Maveric edge 5w40
57 case tractor Chevron sae30
Re: 15w40 or synthetic 10w30 for 115°f temps [Re: leroyd92] #5135063 06/15/19 02:58 PM
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bullwinkle Offline
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Unlimited cooling water supply, most marine engines have relatively low temp thermostats in them, I would stick with the 15W40.


06 Ram 3500 CTD 4X4(FG Venturi), 93 GMC C3500 6.2, 89 F-450 7.3, 98 XJ 4.0(XG8A), 05 xB(XG3600), 18 Transit 3.7, 03 Merc Grand Marquis 4.6 2V(XG2)
Re: 15w40 or synthetic 10w30 for 115°f temps [Re: leroyd92] #5135124 06/15/19 04:56 PM
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Pelican Offline
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Originally Posted by leroyd92
I have 2 boats with 350 engines in them. I've always used 1540 or 2050 in them but I've been curious if I'd gain anything from a full synthetic 10w30.

Engine RPM never goes past 4k

We cruise them at 3k.

My only concern is certain spots of water can we warm especially late in the summer.

What are your thoughts?


Don't they require marine oil?

Re: 15w40 or synthetic 10w30 for 115°f temps [Re: leroyd92] #5135199 06/15/19 06:41 PM
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Audios Offline
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Keep doing what works. I dont think theres anything to gain here except if you were running longer intervals perhaps.


2002 VW Golf TDI-T5 10/30
2007 Mercedes GL320 CDI- M1 0/30 ESP
2005 BMW M3 BMW-Twin Power 10/60
2003 BMW M5-M1 15/50
1998 BMW M3/4/5-M1 10/40
Re: 15w40 or synthetic 10w30 for 115°f temps [Re: leroyd92] #5135202 06/15/19 06:48 PM
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What you could gain is running a straight-weight oil if the brand/weight you want comes in that offering.

Running a winter rating is pointless for a vehicle not started below freezing (I'm making an assumption here about your use of it), and you sacrifice by having a lighter base oil and non-lubricating and potentially shearing VIIs in it.

Re: 15w40 or synthetic 10w30 for 115°f temps [Re: leroyd92] #5135283 06/15/19 08:09 PM
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Jimzz Offline
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15w40 would get my vote. Good all round oil that can handle high heat and even cool temps you may see.


yup
Re: 15w40 or synthetic 10w30 for 115°f temps [Re: leroyd92] #5135336 06/15/19 09:35 PM
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DoubleWasp Offline
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Don't do it. The 30 weight thing has been tried by the manufacturers before. Didn't work. Wear problems popped up like whackamoles.


07 Lincoln Navigator M1 0w-40/FU
68 Charger R/T / Supercharged 440 VR1/DBL7349
07 Ram 3500 4x4 / Cummins 6.7 /DBL7349
17 Maserati GranTurismo Cabrio
Re: 15w40 or synthetic 10w30 for 115°f temps [Re: leroyd92] #5135345 06/15/19 09:50 PM
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Stick with the 15W-40 usage.


Somewhere between Alaska and Wisconsin...
2006 Silverado LT Crew Cab 4WD & 2013 Equinox AWD
Re: 15w40 or synthetic 10w30 for 115°f temps [Re: leroyd92] #5136298 06/17/19 04:37 AM
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alarmguy Offline
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20w50 all the way, way more so for your hot climate.

15/40 acceptable but would prefer 25/40 is you were to go down to a 40.

10w30 to me would be insanity and I think all you would need to do is try it out, then run the boat for an hour or two at 3000+ RPM, slow down and listen to your valves clap.

Most marine engines have 170 degree thermostats in them so it doesnt matter too much as far as water temperature that the boat is running, unless you have closed cooling, then you may have a 190 thermostat..

Oil temperatures do not correlate to water and engine temperature. An engine with a water/coolant temperature of 170 degrees will see oil temperatures well over 200 degrees, there is nothing cooling the oil and your engine compartment is pretty much closed.
This isnt an automobile with 4 smooth rolling wheels, this is a log (boat) being pushed through water with a lot of engine and bearing pressure which greatly adds to the temperature of the oil.

(just my thoughts)

Ps. I always followed the manufacturer which was 25/40 in my mercruisers and now with a Volvopenta engine the book also states 20/50 as an option that I choose to use.
Actually currently using 15w50 Mystik JT8 semi syn this year in our new to us Chaparral.

Last edited by alarmguy; 06/17/19 04:41 AM.

14 Road King (current)
08 VStar 1300 Tourer
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Re: 15w40 or synthetic 10w30 for 115°f temps [Re: DoubleWasp] #5195088 08/23/19 10:48 PM
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another Todd Offline
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Originally Posted by DoubleWasp
Don't do it. The 30 weight thing has been tried by the manufacturers before. Didn't work. Wear problems popped up like whackamoles.


This^. Stick with a 40 weight, and HDEOs work great in marine engines.


2015 Ford F250 Diesel Crew Cab FX4
2017 Ford Escape 2.0
2002 GMC Yukon
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Re: 15w40 or synthetic 10w30 for 115°f temps [Re: leroyd92] #5195112 08/24/19 12:04 AM
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These are 5.7L SBC's or F350 4 stroke ?

Re: 15w40 or synthetic 10w30 for 115°f temps [Re: DoubleWasp] #5199459 08/29/19 02:06 AM
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Originally Posted by DoubleWasp
Don't do it. The 30 weight thing has been tried by the manufacturers before. Didn't work. Wear problems popped up like whackamoles.



Not to mention fuel dilution which will shear that 30w down quickly. 15w-40 hdeo is all I'll run in my 4.3l volvo penta. I think you were the one who turned me on to that a few years ago DoubleWasp. Lol

Last edited by monster1; 08/29/19 02:07 AM.
Re: 15w40 or synthetic 10w30 for 115°f temps [Re: leroyd92] #5202732 09/02/19 10:04 AM
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DoubleWasp Offline
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FD is a big problem for a lot of marine engines. Some ridiculously more than others.

But as previously stated, if an engine does not have a nice big oil cooler, it's oil temps will not correlate at all with cooling water temps.

Plenty of marine engines turn 40 weight into 20 weight in short order. Now take a 30 weight, dilute it, and bring it up to 250+°F. Bad situation.


07 Lincoln Navigator M1 0w-40/FU
68 Charger R/T / Supercharged 440 VR1/DBL7349
07 Ram 3500 4x4 / Cummins 6.7 /DBL7349
17 Maserati GranTurismo Cabrio
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