instrument readings

when I bought my boat I apparently had a bad ground that was affecting my dash instruments. The oil pressure and water temp gauges would peg to the right momentarily when the nav lights were switched on. I cleaned all of the connections to the gauges and the pegging to the right issue went away.

Now my oil pressure gauge has a flutter. The needle bounces pretty much constantly. I would describe the action of the flutter to kind of be like a heart beat or the ticking of a second hand on a clock...about that rapid) Not a wide variation in that I'm concerned about whether there IS oil pressure, just an annoyance thing i'd like to eliminate if possible. Oil pressure (seems to run between 40-60PSI...it looks like if you bring it down off of plane straight to a slow idle, it may get to 10-15 and the little warning light will blink/flash ever so slightly. Alarm doesn't sound.) What causes this flutter and how can I make it go away?

Also, a question about water temperature. My boat seems to run between 145 and about 185 degrees. I'm not concerned that it's overheating, but just wondering how tightly does/should the thermostat/cooling system control the water temperature? I would think that the temperature would be more consistent and would not vary by this much. (By the way, I don't know which thermostat it has in it at this point.) EDIT: I'm wondering if it even has a thermostat in it.

Not looking for problems with the boat, just looking for tweaks that can be done during the week as I look forward to the next weekend.

Steve,
Does this "flutter" speed up and slow down when you increase engine RPM? What's you volt meter doing? Same? I'm wondering about the condition of your alternator. With one of the diodes blown in it's rectification, you would get a half wave DC output out of it. It may be enough to keep the battery charged depending on usage/load but would flutter the gauges.

Steve,
Personally, I sure wouln't take the alternator to a Autozone!! First I would question if they would even have anyone to read the test equipment correctly and second they will tell you it's bad no matter what!! Find a "auto electric" shop and take it in to them if needed.

Your temp sounds about right. Higher when doing some hard running and then cooler when idling around?

Steve,
If the alternator output test confirms a blown diode, they just press in new ones. (there are 3)

Have you done any wire gauge improvements up to the dash? The OEM wiring was always on the light side. Many have run heavier gauge positive and negative feeds to cure electrical problems.

alternator bench tested this morning and checked out fine. can the gauge itself be checked? is the wiring going to the gauge suspect?