Just wondering if any of you guys have dealt with this and might save me some time.

but I'm having an issue that im 90% sure is being caused by either a bad sender or bad gauge.

The boat will have abotu 40-50 psi of oil pressure on both engines when just cruising 3400rpm or so... once i hammer down and get to above 4k i get one engine with a real bouncy oil pressure. I'm talking from 40to 20 back and forth almost sometimes. It is real bouncy where it seems like a gauge or sender. As soon as i shut down its fine at about 30psi hot. I can stay on plan for 45 minutes at 3500 rpm and not have an issue.

It started doing it out of no where towards the end of the season and I never got a chance to put a mechanical gauge on it. I did swap oil filter and even cut it open and it looked just fine.

You could switch the sending unit wires at the gauge if the problem follows its not the gauge. Put that back and then switch the sending units if the problem stay with the sending unit thats the problem. If it stays with the motor you may have oil problems. From what you describe sounds like a sending unit. Hard to test now that winter is here haha

I have that exact same bouncing problem with one of my volt gauges it bounces like crazy sometimes! I'm pretty sure it's the gauge! All new batteries and alternators!! It's a 84 with original gauges

Haider .... check the connector on the sender .....its the push on type and is vibrating at higher rpms ....its on the block @ the oil filter pad .....

I agree, if its bouncing around then its probably a wiring issue. I had issue with mine reading high when hot and low when cold. Turns out the Auto Meter pro comp marine guages don't like merc sending units, I put on a mechanical guage to be sure and yep, they read backwards. My only issue is the sending units are impossible to get to as there on the side of the block, so I bought factor guages that I'm going to put back in.

On a side note I am having a issue with my starboard tach, It's acting like your oil pressure guage. Its fine up to 1500 rpm's after that it goes haywire and bouces all over the place, but mellows out after 3k and runs fine after that. Junk guages.

Yea i was pretty positive it was a wiring issue.. wasn't to worried about it but still want it fixed.

Always to the rescue mike! I have the boat in a heated building down the street so I will have... months.. and months to work on it

I think I would go to mechanical Gauges .....unless you just need to realize that the electric just pretty much show that you HAVE pressure .....not how accurate it is ....My Fuel Pressure Gauges are about 10-20% shy ..... I can log FP on the Holley EFI and its pretty much dead on @ 48-50lbs ....m

I would temporarily rig a mechanical oil pressure gauge to see what's going on with the internals. I had this exact same problem years ago with my 311. Turned out that the pick-up tube had broken off the oil pump and would be fine when cool or cruising, but would be all over the place when warm and rocking it.

Don't just assume it's the sending unit or the gague. The problem you describe could easly be a oil supply problem. Like RedDog said it could be a pick up issue, also, it's not uncommon for a motor to pump too much oil up top and empty the pan when running higher RPM's for an extended period of time. It's why restrictors are put in passages. Put a mechanical gague on it and know for sure.

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