Engine Overheat and/or Electrical Issue

[zman18]

When taking the boat out the temperature gauge went from the normal of slightly above 160 to almost 180 quickly. At one point the temp gauge quickly pegged all the way to the right. No alarm sounded so I feel confident that the temp was no where near the gauge temp.
So far I:
Checked the raw water input hose for blockage before the strainer
Checked under water for blockage on the raw water intake
Tighten the belt
Did an acid flush
Used the laser temp gauge on the exhaust manifold. Reading varied from what I consider normal 165 - 175 but at other times could go up to the 180's
Any thoughts on how to solve this issue? Does this sound mechanical or am I dealing with an electrical issue or both?
I'm considering replacing the thermometer and possibly the temp sender. Appreciate all suggestions

[wolfe10]

I would remove, clean (I like DeOxit) and reconnect the sender wire and the connections at the back of the gauges on the pedestal.

Even if this is not the root cause, it good (and inexpensive) Preventive Maintenance.

[knitchie]

You might check your thermostat. Remove it, soak it in vinegar to clean it and test it in a pan of hot water to see if and at what temp it opens.
Ken
S/V Reverie
2007 C350

[wolfe10]

Actually, if you are going to the trouble to remove the thermostat, clean off the gasket and "work on it", PLEASE just replace the thermostat and gasket.

They do fail and are considered a PM item by many engine manufactures.

But, as I posted above, my first "suspect" is a poor electrical connection.

[zman18]

Thanks for the advice. I'm going to get a new thermostat, clean up the contacts and keep my fingers crossed

[zman18]

A friend mentioned that this problem could maybe be caused by an air lock in the cooling system and suggested bleeding the system. I'm unable to find a procedure in the manual on how to do this. I know there is a bleed valve near the thermostat. Is this procedure listed anywhere. Thanks

[leigh weiss]

I think someone mentioned a bleed/drain valve on the engine cooling lines going to the hot water heater. Look for this cock valve and use it to bleed the cooling system while refilling the top of the manifold. If you have air in this line the circulation of coolant will be poor.

[wolfe10]

Yes, remove the tray over the water heater.

Reach WAY DOWN to the vent valve.

Place a rag or small container under the vent valve.

Start the engine and put RPM around 1200.

Open the water heater vent valve and only close it after no more air/bubbles come out (bubbling becomes a steady stream of coolant).

Tighten valve and reassemble.