hondahp4

hey all, just bought an 87 formula 242ls with 454ci and alpha drive. supposedly it had a NEW factory mercruiser installed just before i bought it...he put an hour of test time on it and then sold it (supposedly!).

now i have some oil pressure issues with the boat. i had it at the lake last weekend and it starts up and idles at 40psi cold. will build about 48psi while cold at 2k rpm. as the boat warms the pressure keeps dropping. after a short run on the lake, it was down about 15-20 at idle and about 25 at most at 2k rpm. since i got it home i have installed a second oil pressure gauge back on the motor and it reads within 5psi of whats on the dash gauge. i drained the oil that was in it (previous owner filled it) and it was still yellow. i figured maybe the previous owner put some lightweight oil in it so i changed it just in case. I filled it with 6qts of factory mercruiser 25w40 oil with factory mercury filter. now after idling on the trailer (muffs) for a half hour, it will start at 40psi and drop to about 20psi at idle, and about 35psi at 2k rpms. this still seems low to me for a brand new motor. i would think it should be about 40 at idle warm and 60 at 2k rpm. any insight on this, or maybe some literature that might settle my nerves!!.............this will be the second boat in a row that i've got screwed on the motor!!!

Airpacker

25 warm at idle is completely acceptable. My concern is what does it have at WOT when fully warm. A general rule of thumb is 10psi for every 1000rpm hot.

hondahp4

i agree that 25 at idle is ok, but i would think it should be alot higher....especially on a new motor. my sbc 350 in my baja that i just sold had 45 idle and 65 at wot when it was new (i built and installed it)....given it settled down to about 35 idle and 50 wot once i put about 50-75hrs on it, which i would be happy with on this motor. i need to get it out on the lake again and load it and see what happens, but i would think it would drop even more once its fully loaded and thus even warmer...if i can only get 35 out of it at 2k while running unloaded on the trailer then im not so sure it will gain much once loaded and hot.....maybe????

bacon1

I'm running a 223 with the 454 and getting 30psi at idle with 20-50 royal purple, I'll check this week to see what my WOT pressure is. I have 360hrs on my motor.

Airpacker

Several things will be affecting your oil pressure other than some mechanical issue. Mercury may have set the bearing clearances a little loose. Mercury may NOT have supplied the motor in question.

Besides that: What is the idle speed? How hot does the oil get? How big is your oil cooler?

hondahp4

If mercury set the clearances loose, then I'm kind of s.o.l. on this. there's really nothing i can do but tear it down and rebuild it (or run it till it blows). it was supposed to be a brand new (not rebuilt) factory mercruiser. who else would have supplied the motor if not mercury? if i take the serial number stamped on the back of the motor to a marina, would they be able to give me more info on it? does mercury factory warranties transfer to subsequent owners?

my idle speed is about 750-800 in neutral...bout 650 in gear and loaded...all the pressure numbers i posted were taken while the boat was on the trailer running unloaded on muffs...i'm not sure of the oil temp, i dont have a gauge for that. the cooler is the factory mercury one thats about the size of two soda cans stacked on top of each other (maybe a hair thinner)

Airpacker

If it is a "production" motor from Merc, GM built it. Mercury only assembles engines from the Racing division.

You can try running the serial # on Bam marines site.