View Poll Results: What oil do you use in your stock power big block ??
25-40
51
9.01%
15-40
28
4.95%
20-50
87
15.37%
straight 40
90
15.90%
straight 30
19
3.36%
syntec
9
1.59%
mobil 1
183
32.33%
amsoil synthetic
45
7.95%
R.P.
21
3.71%
OTHER
33
5.83%
Voters: 566. You may not vote on this poll
POLL: which oil do you use ?
Platinum Member
06-21-2004, 07:45 PM
#23
Re: POLL: which oil do you use ?
Originally Posted by Chris288
I know this had been debated to death, but there is always some GOOD information that comes out of these threads... I was thinking of going with castrol 20-50 synthetic BLEND, I now have 12 hours on a new 496 H.O. The blend seems like the best of both worlds..
Here is a good representation of how conventional oils shear down in the presence of heat and in this case Redline ( and most quality fully synthetics) do not. It shows for example that you can start with a 20w50 conventional and under heat and shear (piston movement) it can go down to a 10w40 viscosity and is comprimised. A conventional 10w40 can shear down to 5w30. The Redline synthetic 10w40 stays a 10w40 and is not comprimised. That's why I use a good 10w40 synthetic in place of a conventional 20w50. Under normal operating conditions they are the same viscosity in essence but more sludge can develop with the conventional's increased volitility and boil off. If you want a 20w50 to stay 20w50 use what Merc supposedly uses in it's big blower motors Amsoil Series 2000 20w50 it will remain a 20w50 under heat and shear forces as will Redline and RP and Mobil-1 to a slightly lesser extent. I think this graph is worth a thousand words. With conventionals you need "thick" because you end up with "thin". Premium synthetics can take the heat and shear forces and remain virtually unchanged. Still change at normal intervals in the marine environment.
Last edited by Hydrocruiser; 06-21-2004 at 08:18 PM.
06-21-2004, 08:05 PM
#24
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Re: POLL: which oil do you use ?
Originally Posted by MitchStellin
Although more costly, the extended life of the oil will offset this cost....by a bit, I change every 50. Thanks for the tech info, like said, why would Corvette use this from day one if it was not the best.
Walmart has 5qt bottles for $19.
06-21-2004, 10:07 PM
#25
AT Cult Member #3
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Re: POLL: which oil do you use ?
I've used Mercury 25w40 since day one. Oil pressure is dead on perfect. I use mercury race filters and change every 10-15 hours. The drive gets changed every 25 hours with merc. hi perf drive oil. 
06-22-2004, 08:31 AM
#28
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Re: POLL: which oil do you use ?
I've got 110 hours on a Sterling rebuild of my 800SC's. They suggested Mobil 1 15-50 Synthetic on a 15 hour cycle. Doug told me that Mercruiser sets their blower motors up "fat" so I should watch for dilution based on how I'm running it. He suggested I do the following immediately after shutting down. SMELL the oil. If you smell gas, change oil filter. Oil level may drop if running hard or raise ever so lightly if lots of idling which is immediate signal to change it. I was running AC PF35's at the time which he thought was cool. I change tranny fluid every 5-6 hours and drive fluid in the #5's every 20 hours. I don't go on plane until oil temperature has stabilized. Probably overkill but in four seasons, the only non-maintenance failure I've had under the hatch is a sheared stud on the power steering pump and two failed battery chargers. For what it's worth
