Yamaha ME421 - overheating

[osprey24]

Took boat out a few weeks ago, done around 12 miles perfectly fine, stopped done abit of drifting stop starting and my low sea flow light illuminated and beeped along with the temperature gauge rising into the red.

Pulled boat out took engine out serviced and checked all pipe work / heat exchangers sent away for cleaning didn’t find anything.

Put it back into the water used it today first time and I have the same issue over heating.

Sea flow is perfect I took the strainer cap off and there’s plenty of flow, replaced impeller when I serviced it.

I think the sensor was faulty in heat exchanger for the flow, cable tied the slider inside up and didn’t beep.

Is it common for the coolant water pump to break / not spin?

It’s perfect idling and stationary with the revs at 2500 for ten minutes it doesn’t over heat only when under load.

Any ideas anyone ?

[Tim M]

Originally Posted by osprey24

Took boat out a few weeks ago, done around 12 miles perfectly fine, stopped done abit of drifting stop starting and my low sea flow light illuminated and beeped along with the temperature gauge rising into the red.

Pulled boat out took engine out serviced and checked all pipe work / heat exchangers sent away for cleaning didn’t find anything.

Put it back into the water used it today first time and I have the same issue over heating.

Sea flow is perfect I took the strainer cap off and there’s plenty of flow, replaced impeller when I serviced it.

I think the sensor was faulty in heat exchanger for the flow, cable tied the slider inside up and didn’t beep.

Is it common for the coolant water pump to break / not spin?

It’s perfect idling and stationary with the revs at 2500 for ten minutes it doesn’t over heat only when under load.

Any ideas anyone ?

You could check the calibration of the sender by removing it and putting it in a cup of warm water (use a thermometer to check the temp of the water) and seeing what the gauge does. Could be a gauge or sender fault if you’re sure the heat exchanger etc is all in good order.

[beamishken]

So are you saying the low flow alarm doesnt go off when its cable tied off but does when its in normal position? If thats the case then its a water flow issue, did you check condition of exhaust elbow as they can block & restrict flow & condition of water hose through the transom?

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[osprey24]

Originally Posted by beamishken

So are you saying the low flow alarm doesnt go off when its cable tied off but does when its in normal position? If thats the case then its a water flow issue, did you check condition of exhaust elbow as they can block & restrict flow & condition of water hose through the transom?

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Yes cable tie the sensor to its maximum flow position and it doesn't beep, so there's definitely a flow issue.

I will check the exhaust elbow later, there's plenty of flow at the strainer cap at idle, makes sense when at higher revs if there's a blockage on the water outlet when higher up the revs it cant flow the water out quick enough causing it to get hot

[osprey24]

Originally Posted by Tim M

You could check the calibration of the sender by removing it and putting it in a cup of warm water (use a thermometer to check the temp of the water) and seeing what the gauge does. Could be a gauge or sender fault if you’re sure the heat exchanger etc is all in good order.

heat exchangers got sent off for cleaning few weeks ago so they are all fine.

Low sea water flow and temp rising is the issue.

I will check the exhaust elbow for a blockage, failing that any more ideas?

[beamishken]

Originally Posted by osprey24

heat exchangers got sent off for cleaning few weeks ago so they are all fine.



Low sea water flow and temp rising is the issue.



I will check the exhaust elbow for a blockage, failing that any more ideas?

Did you check the intake through the transom? The merc ones corrode around the hose & collapse it causing a restriction, not seen it on a Yamaha but its a similar set up so a possibility worth investing. After that I'd maybe fit a through hull pickup system to help increase flow

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[osprey24]

Originally Posted by beamishken

Did you check the intake through the transom? The merc ones corrode around the hose & collapse it causing a restriction, not seen it on a Yamaha but its a similar set up so a possibility worth investing. After that I'd maybe fit a through hull pickup system to help increase flow

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Yes i had the leg off the boat, fitted a new pick up pipe and checked everything.

I'm thinking maybe there's a blockage after the strainer slowing down the flow making the boat think there's not enough flow coming in due to the back pressure ?

any common places where it could block? i did find bits of old anode in the power steering cooler hence took engine out and stripped all the pipe work.

[Roger Barr]

As Beamishken said, check the exhaust elbow, if its the original cast one then they are prone to corroding and blocking the mixer channels.

A quick test with the boat in the water is to squeeze the water pipe at the discharge elbow, rev the engine in neutral, if the pipe goes rock solid you probably have a blockage, definitley woth checking.

I had this, took it off poked and prodded about for an hour and got a load of rust and carbon out, which solved the low flow problem, I replaced the elbow with an aftermarket stainless one soon after.

Another weak point is marine growth in the intake behind the fins.