I’ve already checked the Thermostat and found it to be cream crackered so I’m going to take you through the thermostat and anode replacement on a Yamaha F2.5  outboard engine.

I’ve removed the thermostat cover and the thermostat already.

The anode is quite degraded and there is lots of “Crud” inside the thermostat cover

The screw which retains the anode is seized and will not turn with a large flat bladed screwdriver.

Apply a little heat to the anode with a heat gun, grip the anode with some water pump pliers and gently rotate it just to break the sticktion between the anode and the screw.

Apply a little heat again and the screw will now undo with a large flat bladed screwdriver

 

I’m going to remove the scale from the thermostat cover by soaking it in a mix of warm water and Kilrock

 

It has fizzed away and I’ve taken it out and washed it off with fresh water, given the inside a little final clear out and then fitted the anode, I’ve applied a little marine grease to the threads of the screw and dressed the slot in the screw with a small, thin, flat file.

I’ve used an AVO to check that there is very little (if any) resistance between the anode, anode screw and the body of the thermostat cover

I ran a wire brush over the flaking paint on the mating surface under the gasket, cleaned it with a little thinners, brush painted it with a little etch primer and left it to dry.

Before starting when I received the new thermostat I tested it to make sure it works to the Yamaha Spec, prior to installation just a little marine grease on the rubber grommet to make future removal easier and prevent corrosion.

Fit the new thermostat into the cylinder head

When the thermostat is fitted, you should see the black seal sits slightly proud of the cylinder head.

 

Place the gasket onto the cylinder head, I coat both faces of the gasket with a thin coat of marine grease to make it easier to remove next time and reduce the risk of tearing it and having to replace the gasket.

 

Apply a little marine grease to the threads of the thermostat cover bolts

 

Place the thermostat cover with anode fitted onto the cylinder head loosely fit the 3 bolts, there should be a gap between the thermostat cover and the cylinder head, this is caused by the thermostat seal we saw 3 pictures ago sitting proud, this ensures we have a good seal internally around the thermostat when the cover is tightened down.

Tighten the 3 bolts evenly to the Yamaha specification, which for this is 5.9 ft-lb, tighten them gradually and as you are squeezing both a gasket and the thermostat seal, I would tighten them down gradually to the torque and then re-visit after 5 mins or so to check the torque loading again.  When compete you should just see a little marine grease that you had applied to the gasket squeezed out all around join and there must be no visible gaps which lets you know it’s seated correctly.

You have now carried out an Engine Thermostat and Anode replacement so the cooling system will be much improved and will work far more efficiently.

Next time you run the engine make sure there are no leaks and that the thermostat operates correctly.

Job done