viscosity for jetboat

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Dec 11, 2002
I am curious what others think. My jetboat has a 460 Ford that is almost always running between 3500-5000 rpm's, only run in 77-93 degree weather, and see's 80-120 hours usage per year (summer only in rainy Seattle). I have used straight 40w Valvoline for years, but last year switched to Royal Purple 40w synth (which gave almost 2 mph increase, gps). I always cruise at 1500-1800 and let engine temp come up to around 150-160 before the flogging starts. Is my thinking correct for using a straight 40w for this application?
I don't think a straight 40W would ever be a good choice. I would go with the 5W-40 or the 0W-40 Mobil 1 if you think you need the 40 wt. Also 10W-30 Mobil 1 would be a good choice as it is very shear stable.
What year is the motor? Isn't the Royal Purple a 10w-40? There is nothing wrong with using a straight 40w in those warm temperatures.
I honestly don't see why you would need a straight 40.....what is the highest oil temp? I think this would be great application for Amsoil Series 2000 20W-50. I use this oil in my street turbo and I live way north of you in Lynden. The oil has proven itself to last the Amsoil recommend change interval...which is about 10000 miles in my car. Those temperatures are not extreme, by any measure.(But still seem warm by PNW standards - especially this last summer - we did have a nice fall, but not too many days over 85°F this summer!) [ December 16, 2002, 09:34 AM: Message edited by: Pablo ]
The motor is early 70's, the Royal Purple I am using is a straight 40w. I believe the straight grade will maintain its viscosity better during extended high rpm's operation (and heat) than a multi-grade of the same weight. Keep in mind, I am not concerned with cold starts or fuel economy. There are alot of responses to use a multi-grade, what are the benefits for this application? I am not trying to start a flame, just trying to learn. I don't know what my oil temp is during operation, but the engine temp is typically 160-170. Thanks for the input.
One advantage to the multi-weights is you can get quick lubrication upon startup. The thinner oil will pump quicker. I wouldn't use a multi-grade unless it was synthetic for such a stressfull application.
Newbie here, I tried to post a couple of days ago but something went wrong so I'll try it again. Great forum, a lot of good info. Bigblock I have a mid 70's 460 jet. Here in Arizona in the summer air temps @ 115 degrees water temps @ 80 degrees I will run my 460 between 3200 and 3800 for extended periods of time. Engine water temp 130 degrees, I have no idea what the oil temp is. I average about 90 hours a year. I have been using Amsoil 15W-40 full synthetic for about five years and have had no problems. PC
Big Block, You are not starting a flame here it is just most have never rode in a Pump Boat and heard the demand put on the motor even at very low cruise speed or seen the very very large crank journals of the Ford 429/460 engine series. They are so large they can be offset ground .300 to make a stoker 514 ci just as an example as to how much material is there to lubricate. Stick with a straight 40 wt. You have already seen the merits of it by using it prior " the motor is alive and well " and now seen a MPH gain by changing to a synlube . A RPM increase has occured as well although it would be hard to tell 25-75 RPM in a boat like that. Your water temps are decieving. The internal motor is taking a beating all the time even when merely getting the boat to nose over for plane out leaving the launch ramp these must get gassed pretty hard to achieve,,,Kawasakis they are not [Smile] A cast piston cannot be used in these motors because of thermal expansion,,it will pull the head of the piston clean off above the wrist pin,the piston expands more than the block,getting off topic but Marine engines are misunderstood.Many even use 50wt straight wt oils in pump boats,when these are freshened up the machine shops give them more rod side clearance and grind the crank journals down a little more knowing they live in a different world than Automobile motors.If that motor was in a car the boats rpm and cruise speed of say 35 MPH would be the equivalent of 80 + mph going up hill depending on you impellor size and nozzle size .Stick with the oil that has kept that motor alive to this point in it's life,the high VI with alot of ZDDP [Cool] The RP looks to be a good choice for you
Back in the days when I ran a squirtboat staight HD 30 was about the only choice. Straight 40 was all but unheard of and impossible to find, synthetics had not been invented yet (GOD I feel old suddenly). Dragboat would be the one in the know, hence his moniker.
I looked up the specs on Royal Purple 40w. I want some for my boat. Is this a synthetic? There are only 2 places in all of Minnesota that carry it. This seems hard to believe. Doesn't Napa, Checker, ect carry it?
Thanks dragboat, I think I'll take your advise and stay the coarse. JonS, I have been getting the Royal Purple from Napa for $3.59 qt. or so. The stuff I'm using is SAE 40, I believe RP's SAE series oils are all synth blends. They do have a "racing" series of oils that are full synth (I think).
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