Mercruiser 165 runs great, but shuts off after 30 minutes

New to this forum, thank you for any help anyone can give me in this matter.

Boat starts and runs great for 20-30 minutes at about 2800 rpm. It then sputters and shuts off, similar to a previous post I have read in this forum, with same engine and issues. However, the only addition to the problem is that when you attempt to start it after it shuts down, it will try to turn over and then give you the click, click, click sound (not enough juice sound). After about 30 minutes letting the engine cool down, it starts right up and runs great once again for 20-30 minutes and then shuts down again and the cycle is repeated.

I believe it is a 1980, GM 165 hp, straight 6. It has a new battery, all battery cable connections have been checked and cleaned. I have also replaced the coil. Alternator is putting out 13.8 +/-.. Gas is old but none ethanol, and no water in it. It does have electronic ignition, no points.

It seems I have two issues, engine shutting down and then not turning over till after 30 minutes or so after it has shut down.

Please help.

The click,click sound could be an overheated starter motor/solenoid!!As far as engine shutting off after 20-30 minutes possible overheated coil. Check running temperature of your engine with an infrared temp. gun,maybe one issue is causing both conditions Are battery cables getting warm while cranking,sign of internal corrosion,high resistance.

Thank you for the reply. Let me give you some more information on it.

I did replaced the coil with a new one. As far as the temperature, it runs at 125°. After it shuts down, w/ no water moving through the engine, temperature rises to 150°, according to the gauge.

The starter (like the engine) starts perfectly. It is only after it shuts down, that it falls to turn the engine over.

As far as the cables, I replaced both terminals, though I didn't replace the cables.

the motor should not be running at 120*

The thermostat should be 140* so nominal temps should be 150* during normal operation.

For a raw water cooled marine engine temps above 190* is when issues occur.

What coil did you use?

Is this a point ignition?

Coil must be external resister type for point ignition.

Also if distributor is original when engine is fully warm, pull cap and see if distributor shaft wobbles from side to side.

Common problem with the old inline six cylinders distributors is the fact they are on an angle causing the distributor bushings to wear out causing shaft wobble when hot this will then cause the points to be way out of specification and possible close! This would cause the motor to stall.

If the coil starts getting hot shortly after you start the motor put a ballast resister for power to the coil. If the ignition module pulls power from the coil terminal wire it before the ballast resistor to the coil so it gets battery voltage.

The new coil is external resistor. The coil is not hot when it shuts down. I failed to mentioned thermostat has been removed (no thermostat).

It has Electronic ignition. Will a worn out dist shaft still cause problem with elec. Ignition?

not related to your problem..

Put a Thermostat back in.. it's needed !!

If the engine isn't kept in the proper temp range, it won't perform as it was designed, that's what the thermostat does.

If the engine is over heating after installing the thermostat.. then you have another issue..

as for the click click click.. rent a battery tester and check the Battery Volts and Amps.. seems like it's a bit low or as others mentioned you have a problem with your Starter Motor or Solenoid..

Also check your Volts on the Batt while running, make sure the Altenator is charging.. and check your volts on your Coil while Running.

If you have the electronic conversion then you should be OK... Missed the electronic conversion mentioned earlier.

The issue is with a point ignition, not sure if it could affect a converted system. Worth looking at anyway.

I had an older 1971 Chevy Nova........did two distributors over the years I owned it........both bad due to worn bushings......Point ignitions.


If it simply wont crank then either bad starter or starter solenoid or possibly slave solenoid or possible key switch if NEW battery is good.

After boat shuts down measure battery voltage at battery with nothing on. report back

Also check starter when boat shuts down and see if starter is HOT. If so the starter may be bad.

The issue of sputtering and shutting off is different problem. My first suspicion would be fuel pump. second would be gas tank vent clogged third would be possible anti siphon valve defective or clogged and fourth possibly clogged carb fuel filter.

Topblade said:

The new coil is external resistor. The coil is not hot when it shuts down. I failed to mentioned thermostat has been removed (no thermostat).

It has Electronic ignition. Will a worn out dist shaft still cause problem with elec. Ignition?

Click to expand...

It would cause a problem but not the problem you're describing.. Very likely have loose or poor grounding. Check starter connections and possibly redo as well as main grounding connection at engine.

try a voltage drop test, Place one lead of volt meter on battery + post and other lead of voltmeter on battery + post of starter. turn key and observe reading,Any more than.3 volts on meter,possible faulty battery cables. Do the same test with negative side, - post of battery to body of starter,