Oil for 2005 4.3l - 19' Fish/Ski Boat

[scottjima]

I have a 2005 Tahoe Q4SF w/ the 4.3L Mercury 190HP engine and Alpha outdrive. I am currently running M1 5W40 Truck/SUV which is a diesel rated oil and an AC Delco filter.

My typical use is in Texas w/ 90 - 100 degree days. We will idle allot (fishing, etc.) and ski/tube as well. I do tend to run at higher speeds when crossing large lakes (40 mph and 3500 rpm)

I spent last weekend on Possum Kingdom and ran from one end to the other at speed. (45 minutes) The engine got good and hot and the oil pressure never dropped below 45-50 at speed. This means the oil is holding up and not breaking down, correct?

Do you think the M1 5W40 oil is a good match? It is diesel rated and the engine does seem to start a bit easier when cold. I am also running LC and FP in this engine.

 

[terminaldegree]

Where was the oil pressure at idle after that run? How high was the water temp at speed?

You're probably ok with that oil. The viscosity "spread" is wider than I'd probably want for the marine duty cycle. Were it my boat in the same conditions I'd run either 15-40 year-round or a straight 40 weight for the warmest 8-9 months of the year, but I'm rather on the traditional side with this stuff...

45 minutes @ 3500 on a light boat with that motor is perfectly fine. Don't worry about a thing.

 

[Schmoe]

Ahhhh Possum Kingdom, Fort Sill used to lease that area out years ago. Never got a chance to go down there, but heard it was pretty nice. I bought an acre in Bridgewater, OK right off of Lake Texoma.
First, that engine in that boat will do you great. With that speed, I will assume your running about a 18 pitch prop. Could get more speed with a higher pitch prop as that engine will handle it and is a torquey motor. I personally feel a 5W-40 wt. is too large a spread and oil will breakdown quicker. I ran Vavoline Racing 15W-50 one summer and it constantly pegged the oil pressure guage at 60, but dropped really low when idle. Like the above mentioned response, check the oil pressure after a long run. You'd like it to be at least 25 to 30 psi. I wouldn't worry about heat unless you loose your impellor and the engine overheats. Water temperature will barely get above 85 or so.
Through the years I've experimented with different weights and manufacturers and have found that Penn. LL 15W-40 works the best.

 

[scottjima]

Thanks for the responses...

I am actually running a 23 pitch SS 3 blade prop. I probably should have gone w/ a 21, as there are usually 4 - 5 of us on board. I can hit 50 mph with little weight and about 48 with my family of 5 (and all their stuff) on board.

The oil pressure after the 45 minutes of 3500rpm was over 40psi. However, this oil is still "new" with only about 5 hours on it. Also, the temps were in the 70s. Engine temp was 170 steady and will hit 180 if I run it really hard.

I had purchased some Pennzoil LL 15W40 to put in the boat, but ended up putting it in my tractor... Guess I'll watch things and see how it goes. I don't really want to dump the oil as it has very little use on it.

 

[Schmoe]

oopppsss, didn't check the rpm's at that speed, should have known better. A 21 would get you out of the water quicker but those SS props don't flex any at all. I ran a 21 pitch 4 blade comp. prop last summer and really liked until it hit a rock and shattered. But, it didn't harm the alpha outdrive at all. Went back to a 18 pitch 3 blade aluminum for the time being.

 

[scottjima]

Well, so far my skeg is the only think that has met an early demise... I now have a skeg guard. With all 5 of us, we can hit 48 at 4200. I can hit 50 at 4400rpm by meself. I think since I am at the min RPM, I would be better off w/ the 21. I would also benefit with the additional holeshot.

I also added SmartTabs last year. They made a world of difference, and I suspect they could be adjusted a little to improve all of the above.

I carry my stock 23 pitch al. prop just in case...

 

[Slick17601]

That should be a good oil. Amsoil Diesel & Marine 15W-40 would work well also.

 

[Turk]

"Next Time", try the Amsoil for Marine engines ! I love it.