Advice needed - low water pressure and cold engine temps

akis

Recruit
Joined
Jul 31, 2013
Messages
5
Could anyone please help me with the following problem

I have 2 Mercury Verado engines, 2009.

Today I noticed that the right engine is cooler than normal, and cooler than the left. Usual temps are about 60C-70C but the starboard engine was at 40C-50C. Water pressure on the port engine is 0.25 bar and on the right engine it is 0.07 bar. Water coming out of the discharge has visibly less pressure than the other engine. Oil temperature and pressure was equal and normal on both engines.

I asked a mechanic and he said that most likely the thermostat is stuck and that is why the engine runs cooler. And at the same time some piece of debris blocking the telltale resulting in diminished stream. He said to ignore the water pressure indicator and to run the engine as normal.

I am not sure I agree with this explanation and am worried that something else has gone wrong. For example maybe the impeller is half-broken and does not generate enough water pressure. As there is not enough pressure, water does not make it to all the chambers it should pass through, and does not pick up all the heat from the engine, thereby reporting lower engine temps. And if this is what's happening then the engine could be irrecoverably damaged as parts of it are not getting coolant flow.

The boat is currently in the water and is a major pain to take it out for diagnosis. Any advice would be welcome.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,398
If the cooling system is like other Mercs, the idle temp is controlled by the thermostats. At 2000RPM or so, water pressure pushes the poppit open, adding lots of cooling water and lowering the water pressure.

You might run both engines up to temp at idle and see what the temps are. if they are normal, the thermostats are working properly. Then rev them up to about 2000RPM and recheck the temps. If the one engine loses temp at that speed, perhaps the poppit needs repair/replacement.
 
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