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Oil for older carbed 350

R

Rscottdds

Regular Contributor
I live in Southern California where it rarely gets below 50. I’m usually running the boat in temps between 60 and 75. The engine is 30+ years old but only has about 800hrs on it. It does use a bit of oil each trip.

Whats the best type of oil for an older carbed 350 in the above conditions? Is it best to run as thick an oil as possible? Single vs multi viscosity?

Thanks for any help.

Robert
 
What is your oil pressure at hot idle and under way. You want 10 psi per 1000 rpm. If the engine is still tight and make s40 psi at 4000 rpm then 30 wt is ok, if the bearing clearances are looser run 40 wt or 50 wt to keep oil pressure up. Personally I run 15 w 50 or 25 w 40 in my 5.0. Do t have many hours but I find when I’m really on it for long periods the oil pressure drops a bit, doesn’t happen with 50 wt.
 
If not a heavier straight weight, then a 20/50. Avoid synthetic as that may knock stuff loose....like gunk, carbon, and other deposits. Marine engines run cooler and can build deposits. They need more frequent oil changes and should be drained when motor is at operating temperature.....as warm as possible. That way the oil will carry away the suspended particles and they won't stick so much inside the oil pan. Many operators, or mechanics drain oil when motor is already too cool. Suction systems don't get all the crap out either. That's why marine stuff lasts maybe 4000 hours and the same motor in a truck/car, running 195 degrees will last 10,000 hours. Granted the motor in an automotive application is only running 2 to 3 thousand rpm......still that doesn't make up for the hours.
 
A few clarifications, and in no certain order:


Minimum oil pressure at idle speed would be 10-15 psi.
Max oil pressure should not exceed 60*. Cavitation (at/near the oil pump) may occur if pressure exceeds that.
Chamfering of the oil passages can be done to help reduce the likelihood of cavitation.
(Bill Jenkins did extensive research on this in the late 60s)

Marine engine operating temperature will vary depending on the cooling system (i.e., Raw Water cooled -vs- a Closed Cooling System) and the water that we are operating in.
Examples:
RWC SBC in ocean water should run no warmer than 145* to avoid salt crystallization.
RWC SBC in lake/river water can run at 160* with no issues.
Closed Cooling system SBC operating in any water can safely run at 160*/180*.

Oil viscosity is measured at a given oil temperature. This is oil temperature, not necessarily coolant temperature!
You will find an array of suggested operating oil temperatures.
On average, 185*-210* is acceptable. Let this and engine operating temperature be a factor when you choose a viscosity.

The 25-40 viscosity sounds about right to me.


The SBC oil pump is a semi-positive displacement pump, and is capable of producing up to 200+ psi.
The spring loaded relief valve controls the pressure that the oiling system sees.
The oil pump will produce more volume than what a healthy SBC engine will require.
While we may read that the general rule is 10 psi per 1K RPM, the relief valve should prevent excessive oil pressure.


I'm not aware of synthetic or synthetic blends "knocking stuff off" that would not be captured by the oil filter as the oil returns to the oiling system.


I agree with Tim in that you will want to pull/drain the oil while it is hot or at least very warm.

Your best scenario will be a remote oil drain hose that is connected to the oil pan's drain plug port. Not a Whimpey hose, but a larger inside diameter hose.
There are a few great suction devices out there that do a great job.
I use the Tempo Oil Boy oil extractor.
Fully mechanical.... no electric pump and no power to connect up.
Connect to remote drain hose..... pump the handle...... sit back and watch the oil being extracted.


shopping
 
Excellent info, Rick. Thanks for the clarification.
I have actually seen where materials that get " broken down", can partially plug the oil pump's pickup screen........never get to the filter.....then what also can happen, is that the filter can get restricted....allowing excessive bypass of the oil....you get the idea.....then contamination passes around.....often effecting hydraulic lifters first. Reduction of oil pressure.....???? Yes!
 
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Marine engines work very hard and some parts run hotter than an automotive engines.------They run / work hard based on the amount of fuel used.
 
Agreed, Racer. They really get a workout. Sadly enough, however, sometimes they are not rewarded with proper maintenance.
 
timguy said:
Agreed, Racer. They really get a workout. Sadly enough, however, sometimes they are not rewarded with proper maintenance.
Click to expand...

Tim, that is certainly the truth!

I think that some owners pay more attention to their home entertainment centers than they do to their boats.
 
the main thing with marine inboards is to not use a auto application based oil like a 5/30 or 10/30 they will probably thin out after sustained high RPM use. Mercruiser, Sierra and Lucas Oil all make a 25/40 marine oil that is fine for your engine. The other factor is zinc content, this has been significantly lowered in recent formulations, if you look at oil analyses, I know for the Merc/Quicksilver oil the zinc content is approx 950 or so PPM, because I did an oil analysis on it a few years back. Now if you have a roller hydraulic cam it really doesn't matter but for an older engine with a flat tappet cam, higher zinc is a benefit. Lucas does make a higher zinc motor oil that will address that concern.
I have a roller hydraulic cam in my old '88 4.3 V6 and have been using the Merc/Quicksilver oil for a long time and it has done well by me. Oil pressure readings are all normal and consistent.
 
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