I noticed that last time out that the pressure guage was low, then went back to normal. Ten days later the guage doesn't work. I checked the water flow while on the lift, and it seems like I am getting the same flow at least at idle. I ran the boat and noticed that the side that the guage wasn't working was running about 10 degrees warmer than the other side (130 starboard, 120 port). This is after a rather hard run to 5,000 rpm for awhile. The mechanic said that probably a piece of rust is stuck in the hose from the engine? And, just to watch my water temp. Is this ok to let go until mid season when I have the oil changed? Does this happen with often with water guages, or should I have it looked at right away. I think that the temp would have really spiked if it wasn't getting ample water? Thanks.

Depending on where the gauge is connected (block), they tend to plug easily. Connected to the intake is less likely to plug up.
Keep an eye on water temps till you can check it.

easy fix is remove line from back of gauge and hit it with compressed air to clear it out. DO NOT apply compressed air from the engine end of the tube with it connected to the gauge.

Every Fountain I have ever worked on has the water pressure gauge hooked up to the drain hole in the bottom of the block. It will get dirt, silt, rust, etc. in the fitting where the hose connects. Some of them are tough to get to in order to clean out the fitting.
As Airpacker said, remove the hose from the gauge and blow compressed air through the hose. This should clear it out, at least temporarily. The permenant fix is to hook it up to the intake as Mr Gadgets said. Good luck.
Eddie

That will fix it.

Thanks for the replies. I will try the temporary fix for now.

Last time out it went up to 5 and stayed there even when I shut off the engine. Is this a bad guage or just a piece of rust from the engine stuck in the hose?

Something is stuck in the hose. Disconnect it from the gauge and the engine and blow some compressed air through the hose from the gauge end.
Eddie