Quote:
Originally Posted by Sunset Bob
I have a 1997 Larson that on a cold start has good oil pressure but after about 15 minutes of running at about 3000 rpm oil pressure starts to drop(about 20 PSI at 3000 rpm not good need 10 PSI for each 1000 rpm) Pull throttle back to idle and 0 oil pressure.
Engine burns no oil
Engine has plenty of fresh oil
Engine has no bearing noise
Engine does have some lifter noise at 0 oil pressure
WHAT NEXT
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SB,
First of all, there are several people on the Forum who have given sound marine engine advice and hopefully, they will participate in this as well. Having said that, it is my experience that what you are describing is not uncommon, at least for me, in that vintage of boats that I had. Depending on what type of engine you are describing, 4, 6, or 8 cylinder, and depending on your mechanical ability, the first thing I would do is remove the oil pressure sending unit and attach a manual oil pressure gauge ($10-$30 bucks on EBay)to the engine and perform the same test. Then you will know for sure by eliminating the sending unit and the dash gauge.
When a marine engine cranks out 3000 rpm it thins out the oil pretty good and then a sudden pull back of the throttle will give you a low oil pressure reading. For those of you reading this, try it sometime and watch your gauge, you'll be surprised.
There are many other factors such as the type and viscosity of the oil you are using, when it was last serviced, hours on the engine etc. I'm going to assume you take good care of your boat. The oil pressure test right at the block is a great way to start diagnosing. Hope this helps.
Blue Thunder