Oil Pressure Gauge/warningLight

[88SupraComp]

After warmup of my 88 supra comp PCM 351, the oil pressure gauge reads very low, and the oil light will come on when the boat is idling and in gear. (lower RPMs) As soon as I hit the throttle a little bit, the pressure goes back up to normal levels. I am using a high quality 10W40 oil. This problem had only been sporatic in the past but now it happens all the time. The engine seems to be running strong, and I can't hear any knocking, pinging or anything else. 485 hours are on the engine. Is this a normal operating condition?

thanks,

Jeff

[OUI]

Low oil presure is not normal. However, if you don't hear any clattering from the rod bearings it could be as simple as a bad sending unit -- especially if it was sporatic in the past. Get a new one of those they're cheap and it's a good place to start.

[SupraTom]

I have a 85 comp with the same engine. When this problem happened in my boat It turned out to be a bad oill cap gasket. Make sure you check this out before you change your oil sending unit.

[88SupraComp]

Thank you for the tips guys!! I will be out on th water tomorrow to check it out.

Jeff

[Dinoz]

I noticed on my '89 comp with the 351 that when the engine is warm, the pressure sit's around 20 to 25 psi, then with the rev's up it is at the 40 to 60 psi range.

What should the pressure be at when you are idling? When I check the oil level (cold), it looks like I have too much oil in it. Also noticing some blue smoke on acceleration...

Any advice??

DZ.

[OUI]

Blue smoke indicates a rich mixture on the carb. Your oil presure sounds normal to me. When your motor is cold all the oil drains into the pan, if it shows too much oil there's too much oil -- because that's your true reading. However, a little over the line wouldn't hurt -- a lot over the line could cause problems.

[IndyMatt]

Just a poll for anyone, maybe somthing effecting pressure readings, Idle vs WOT... My 04 Sunsport recommends 15-40; but my dealer said that 25-40 was actually better suited for the marine environment. Thats is what ive used (same thing the local mastercraft dealer suggests) and have had no problems. Im just curious how the different weights affect pressure. I too notice a fluctuation in pressure upon acceleration, but I believe this is normal. Also I have always been told the best way to check oil is to run the motor to opperating temp then after shut down, check levels approximately 5min later. In regards to the blue smoke, your burning oil. As someone mentioned it could be too much oil being mixed with fuel; another possibility if you typically have too much oil in the crankcase, additional pressure will cause oil to leak past the rings and into the cylinders. Check and make sure your plugs are not oil fouled.

[Dinoz]

Thanks for the info guys.... After running thie weekend, I did check the oil both when it was cold, and also at running temps. The level showed to be the same, over the "full" mark.

When I start the engine cold the PSI will be around the 40 psi mark, when I'm running at 3,000 rpm it will be around the same mark, then after running for a bit, back down to idle the PSI will be around the 15 to 20 psi range.

On a different topic, I have noticed a "knocking" sound coming from where the shaft meets the transmission, right around the coupling. I noticed when I'm in gear there is some wobbling in that area, but when I run the boat for a bit, the knocking sound goes away. This one has my stumped. Any advice??

Thanks,

DZ.

[wakespeak]

Couple of comments and recommendations:

- Do not use 10w-40 in a marine engine unless synthetic. The oil will very quickly breakdown. You'll be left with 10w-30 or less, and sludge. Use 15w-40 diesel oil like Shell Rotella, Chevron Delo, Pennzoil Marine, or Mobil Delvac (all of them are rated for gasoline engines too). Mercruiser's 25w-40 is good too. These are much better built oils for heavy duty use. They have the right base oils and additives for your engine. Straight 40 is fine/preferred if temps stay above 60F.

- Do not overfill! The oil is splashing around as it is. Overfilling puts the level up near the spinning crank. This whips up the oil and you'll loose pressure due to the air in the mix.

- If the above 2 don't fix your pressure issue, then suspect 1) the oil pressure sender, 2) clogged oil pickup screen, 3) worn out engine bearings, 4) loose oil pickup. For 2, try running Redline oil for 50 hours. It is an ester based oil that will dissolve the crud. Easier than dropping the pan and cleaning the screen yourself.

[88SupraComp]

My 1988 Comp owners manual states to use 10w30 in colder weather and 10w40 in the warmer weather.
Last year I used marine grade Quicksilver 25w40 per the supra dealer and it ran a little better than this year with the 10w40 per the owners manual. What are the main differences in oils? and why would the owners manual recommend an oil that is not as good for the engine then the 25w40?

thanks for anyones assistance,

Jeff

[wakespeak]

Quicksilver 25w40 has no viscosity improvers. It is a blend of straight base oils. That is why Mercruiser is adamant about using it. Marine engines work at high constant loads that will shear viscosity improvers. They also dilute oil via carbs that are set up to run a little rich and aren't clean burning at idle.

In 1988 10w-40 was commonly available, but was found to shear down fast and foul engines. Both PCM and Indmar require 15w-40 oils now, albeit for the GM small block.