Mercruiser 4.3l oil

[Nola_mike]

Looking for oil for my 4.3L mercruiser. I got the block from a high mileage blazer, unknown history.
I had used rotella/delvac 15w-40 conventional oil in the 3.7l that it replaced. Wondering if I should continue that, switch to a supertech full synthetic for the same price, or ...

Filter was going to use a fram tg unless there's a better option.

Oil changed every season, probably 50-100 hours.

 

[MacManus99]

Keep rolling with whatever flavor 15w40 tickles your fancy.
For low hour use, I prefer a cheap HDEO that is changed at the end of every season, as part of winterizing.

 

[Rand]

My Opinion:
boat motors arent used like car motors.. who floors the go petal in their car for 10min at a time.

Your best option is a thicker oil than spec'ed for car use.. 15w40 is a good choice.

 

[dadto2]

I also have a 4.3 Mercruiser. The Quicksilver 25w40 that is spec'd is cheap enough at Walmart that I just use that and don't worry about which non-marine oil I think would be better. I believe that West Marine and Bass Pro each carry a house brand 25w40 marine oil at a reasonable price too.

 

[ka9mnx]

15w-40 is fine. The marina I worked at years ago used 10w-40 (no thinner!).
The marinized 4.3L has a hotter camshaft and the balance shaft GM added to later 4.3L engines.

 

[Rand]

15w-40 is fine. The marina I worked at years ago used 10w-40 (no thinner!).
The marinized 4.3L has a hotter camshaft and the balance shaft GM added to later 4.3L engines.

That's interesting, his block is from a high mile blazer.. I wonder what other differences there are.

 

[thastinger]

I have a 4.3 I/O, badged as a Volvo. I've ran M1 15-50, Rotella 15-40 and M1 Euro 0-40 in it, all seemed fine.

 

[thastinger]

That's interesting, his block is from a high mile blazer.. I wonder what other differences there are.

The intake manifold is cast iron and it has 2 plugs in the block so you can fresh water flush the block while on the lift or drain the block for winter.

 

[DriveHard]

always used Delvac 15w-40 in my marine engines...never had a failure

 

[alarmguy]

If I was going to use a non-marine multi viscosity oil I would not go any less than a 15/50.
I use Mystic JT8 15/50 (semi syn)
Also available M1 15/50 (full syn) might be an option or any straight 40
Quicksilver 20/40 which for all intent purpose is a straight 40 too

 

[ka9mnx]

That's interesting, his block is from a high mile blazer.. I wonder what other differences there are.

I don't know when GM added the balance shaft to the 4.3L. As for the marine camshaft, no. The camshaft was usually spec'd by the company marinizing the engine and was a custom grind.

 

[Donald]

My Opinion:
boat motors arent used like car motors.. who floors the go petal in their car for 10min at a time.

Your best option is a thicker oil than spec'ed for car use.. 15w40 is a good choice.

Many times it's hours not 10 minutes at high throttle.

 

[Nola_mike]

I don't know when GM added the balance shaft to the 4.3L. As for the marine camshaft, no. The camshaft was usually spec'd by the company marinizing the engine and was a custom grind.

Not sure that's the case, much debate on the boating forums, I'd love to see specs.
Other differences between marine and auto are composite or ss head gasket and brass core plugs. By 2001 the blazer block had both. The block drains are on the auto block as well. Balance shaft engines came out in 92, vortec in 96.

 

[dlundblad]

Since it’s a high mileage engine, I’d entertain Maxlife 20w50 if you can still find it otherwise just a 15w40.

 

[alarmguy]

Since it’s a high mileage engine, I’d entertain Maxlife 20w50 if you can still find it otherwise just a 15w40.

I agree with the 20/50 even if Maxlife can’t be found, forgot to mention it in my other post.

 

[thastinger]

I sometimes think we overthink oil in these motors. 4800RPMs is max assuming you have the correct prop on it with operating temps very low compared to on-road versions.

 

[MacManus99]

I sometimes think we overthink oil in these motors. 4800RPMs is max assuming you have the correct prop on it with operating temps very low compared to on-road versions.

It's not so much RPM or temp that causes us to overthink, it's load. Marine engines are subject to MUCH greater loads than automotive, and must endure these loads throughout it's service life.

Also, coolant temp and oil temp are not correlating.

 

[alarmguy]

Also, coolant temp and oil temp are not correlating.

^^ BINGO^^
Thank you. Its a common misconception that they correlate

 

[thastinger]

It's not so much RPM or temp that causes us to overthink, it's load. Marine engines are subject to MUCH greater loads than automotive, and must endure these loads throughout it's service life.

Also, coolant temp and oil temp are not correlating.

Disagree. Prop will slip long before you bog the motor with load, even a Bravo 4 blade SS 14.5x19 pitch, with the exhaust holes fully closed, will slip before a 4.3 gets loaded down. You might be able to load one with a 3 blade 21 pitch, but that is probably not the correct prop for your boat if it has a 4.3 motor.
You don't "load" 4.3s, they come in boats that weigh 2K and 21 ft or less.

 

[alarmguy]

Disagree. Prop will slip long before you bog the motor with load, even a Bravo 4 blade SS 14.5x19 pitch, with the exhaust holes fully closed, will slip before a 4.3 gets loaded down. You might be able to load one with a 3 blade 21 pitch, but that is probably not the correct prop for your boat if it has a 4.3 motor.
You don't "load" 4.3s, they come in boats that weigh 2K and 21 ft or less.

Ummmm ... very good point about the slip but would disagree to suggest or maybe imply a marine engine has the same load as a vehicle with wheels if I am understanding your post. But I think you maybe suggesting physical bogging down of the engine by improper propeller, vs the high load of pushing a barge (boat) through water. MeCruiser does note the tremendous load marine engines are under.
Oil temps will run far hotter, also taking into account the high RPMs and huge gas consumption compared to a car..

Also the 2,000 lb weight you mention is too light, A 21ft Chaparral from the factory with this engine weighs in at 3,100 lbs dry weight.
Throw in a full tank of gas 240 lbs, plus the boat has a passenger capacity of 1,600 lbs. You can be pushing close to 5000 lbs.

These engines are also used in twin configurations for boats weighing twice the dry weight mentioned above.