Engine oil pressure decreases as rpm's increase

[Surfdad]

I just purchased a 2005 SV211 air Nautique. It has only been run once in the last 2 years. Has very low hours - 144 hours. I Had an engine tune up done and the oil and filter changed at a local dealer last week. Engine seems to run fine, but when I run down the lake and increase the rpm's to 3,000, the oil pressure decreases to around 46 psi. When the rpm's get up to around 3,500, it decreases further to 42 psi. At 4,000 rpm's, the oil pressure starts to drop and doesn't appear to stop. When it hits 20 psi, I reduce the rpm's back to 3,000 and the oil pressure increases back to around 46 psi. Any ideas of what can cause this??

[NautiqueJeff]

My guess would be faulty gauge or a bad ground at the gauge or the sending unit.

[Surfdad]

Thanks for the reply. I'll ask the servicing dealer to check those.

[Jonny Quest]

If the gauge is working, you could have a serious problem. Oil pump could be failimg. Low oil volume can also produce those symptoms. Also check sending unit.

JQ

[BrickBrock]

I have noticed something like this immediately after an oil change. I suspect my issue was an air pocket residing at the oil pressure switch location (there is a tee here). I would also reduce throttle when the pressure starts to drop and the the pressure gauge would climb back up to normal. After repeating this a few times the oil pressure would read normal and would climb with increased rpm (I suspect the air pocket cleared the tee at the pressure switch location and was now filled completely with oil, thus reading properly).

[Surfdad]

Thanks to all for the reply's. It has the digital and analog gauge and both match exactly as the pressure rises and falls - so I assume the gauges are correct. Last night I checked the engine manual and it states that the crankcase oil capacity with a new filter is 4 quarts. The oil is showing high on the dipstick. It appears that the mechanic put 5 quarts - approx. 1 quart to much oil in it. I assume this would cause the oil to aerate (I think I'm using the correct term here) and I think this would cause it to lose pressure at higher rpm's. I'm going to reduce the oil level to the full line and run it again. I checked and It does have the correct weight oil and the correct oil filter in it. Could I be on target here with my diagnosis of too much oil?? Could this cause additional problems that I should be aware of or check out?

[jkallen21]

I just googled: overfilled oil "low pressure" and a lot of people are in the same situation. So my thought is that it certainly can cause what you're seeing. Two things you should keep in mind:
1) Too much oil can ruin the engine. Keep your receipt of the last oil change if you still have it. If not, maybe asking for a copy prior to telling them the situation would be wise.
2) Both gauges are hooked to the same oil sender. There is a single wire on the sender that feeds them both. You can remove that wire, turn the engine to the "on" position, but not running and touch the wire to the block. Both gauges should go to full pressure. This is not a test to determine a faulty sender, but it gives you a good idea that both gauges are operating somewhat normally.

[scottb7]

Sorry, but I don't think a little too much oil is your problem. My experience with my 343 is that unless you go somewhat higher than full on dipstick then you get low oil pressure warnings.