OMC, 4.3L, V6 engine oil change

[Bob01]

I have an OMC stern drive 1988 (inboard/outboard), 4.3L, V6 and trying to change the engine oil. Manual recommended 30W. I need to know what people actually using now as an alternative? Thanks.

 

[harringtondav]

Straight 30W engine oil is common as nails. But I'm surprised at OMC's 30W recommendation. The 4.3 is a GM engine used in Merc stern drives. They recommend 'their' 25W40. I'm away from my manuals now and the 4.3 viscosity/temp chart. But any multi viscosity 15W-40 is a preferred alternative. I use Valvoline syn 20W-50. but their std 20W-50 is fine for annual oil changes. Marine engines run at higher ave. rpms than auto engines. 40W seems prudent.

 

[PITBoat]

I have seen Shell Rotella T4 15W-40 heavy duty diesel engine oil recommended here. Sounds good to me so I bought some. I wouldn't hesitate to put a quality straight 30W in there either.

The manufacturer of the Suzuki bikes I used to ride recommended 10W-40 (right on the dipstick), but people swear by Castrol 20W-50 for bikes. Who's right?

We were in a "Very Low" probability area for tornadoes this evening. But they were sounding the sirens tonight, and the weather guys on the news were looking at potential tornado producing storms in the area. We got a good one a few years ago on a "Low" probability day...

 

[Bob01]

Straight 30W engine oil is common as nails. But I'm surprised at OMC's 30W recommendation. The 4.3 is a GM engine used in Merc stern drives. They recommend 'their' 25W40. I'm away from my manuals now and the 4.3 viscosity/temp chart. But any multi viscosity 15W-40 is a preferred alternative. I use Valvoline syn 20W-50. but their std 20W-50 is fine for annual oil changes. Marine engines run at higher ave. rpms than auto engines. 40W seems prudent.

Thanks, I will go with Marine Oil, 25W40.

 

[Bob01]

I have seen Shell Rotella T4 15W-40 heavy duty diesel engine oil recommended here. Sounds good to me so I bought some. I wouldn't hesitate to put a quality straight 30W in there either.

The manufacturer of the Suzuki bikes I used to ride recommended 10W-40 (right on the dipstick), but people swear by Castrol 20W-50 for bikes. Who's right?

We were in a "Very Low" probability area for tornadoes this evening. But they were sounding the sirens tonight, and the weather guys on the news were looking at potential tornado producing storms in the area. We got a good one a few years ago on a "Low" probability day...

Thanks

 

[Scott Danforth]

back in 1987 when your 1988 motor was used, the recommendation was straight SAE 30

however the oils also were high in zinc back then too

since then each manufacturer recommended a different oil for the same motors. SAE 30 to SAE 40 to 20w-50

the 15w40 diesel oils still have high zinc in them. that is my go-to oil for most things I own if I do not have SAE 30 on hand. I buy it by the case.

(do your own research on why zinc is important to heavily loaded flat tappet motors)

 

[Bob01]

back in 1987 when your 1988 motor was used, the recommendation was straight SAE 30

however the oils also were high in zinc back then too

since then each manufacturer recommended a different oil for the same motors. SAE 30 to SAE 40 to 20w-50

the 15w40 diesel oils still have high zinc in them. that is my go-to oil for most things I own if I do not have SAE 30 on hand. I buy it by the case.

(do your own research on why zinc is important to heavily loaded flat tappet motors)

Thanks

 

[matt167]

That's a negative on high zinc levels in Diesel oils anymore. Since this latest CJ rating which came a few years ago. Shell Rotella is higher than others still though.

However Valvoline VR1 20W50 would work perfect. It has 1200 ppm of ZDDP in it. There is also a zddp additive that is available at Advance Auto in a yellow bottle for $9, and 1 bottle will convert a 5 quart fill of standard oil to 1,500-1,800 ppm. I run that along with conventional 20W50 in my MGB

 

[Lou C]

A 1988 4.3 will have roller hydraulic lifters and the need for high levels of zinc is not an issue like it can be with flat tappet cams. I know for sure that the ‘88 is a roller cam because I did a top end overhaul on mine 2 years ago...
I use the Merc 25/40 conventional oil.

 

[Scott Danforth]

Dave, 1988 was a cross-over year as that is when 4.3s went roller along with the auto 5.0 and 5.7 (trucks coming later) Many boats still had 1987 motors (flat tappet) in 1988