[Captain Steve]

Last Sunday was probably the last trip of the year for me. The nights will be longer than the days when this weekend is over. Anyway, on Sunday I noticed that my temperature gauge was indicating either 170 F or about 240 F. It just jumped from one reading to the other, switching back and forth about every 20 seconds.

Everything else seemed OK. Plenty of water coming out of the thru-hulls, exhaust manifolds feeling only nicely warm, and no engine alarm. My lower unit water pump was replaced 2 years ago and Alpha water pump impellers are usually good for at least 5 years. They are big and floppy. I replaced the automotive water pump on the 5.7LX last year using a unit from Autozone when I noticed that the OE water pump was leaking from a weephole.

The fast switching between the temperature readings might be the thermostat opening and closing, but I didn't think they open and close that fast. And this did not happen the weekend before. I am supposing that it is time for full service. This Alpha has never been off, so the gimbal and U joints have never been inspected. At 12 years old I am thinking new bellows are in order.

Any ideas, suggestions, insights, or recommendations will be greatly appreciated.

[WetWilly]

Hi Captain Steve,

I would check the wiring and the connections from the sender to the gauge first, if all seems OK, then I would start by replacing the Temp Sender.

Make sure you replace the right one, many of the Mercruisers have two (possibly three with Fuel Injection), one for the alarm and one for the temp gauge, The Temp gauge sender I believe should have a solid "Tan" colored wire at the motor, not a "Tan/Blue", which is for the alarm or solid "Yellow", which is for the the computer.

Let us know what you find.

Good luck,
WetWilly

[Captain Steve]

Sir Wet,

I was beginning to think my BO was coming through the internet. Thanks for responding. My thermostat gooseneck has two wires. I will look into a new sender for the temp gauge as you suggested. Next step will be a new thermostat. Then winterization. Then a subzero hell with lake effect snow.

Thanks again,