Boat Issue



The boat and beginning:



1996 Formula 336 SR1 w/ 7.4 MPI with under 200 hours and completely stock. No performance upgrades.



Had battery tender cables that were left on upon starting and the port side cable got wrapped in the belt and broke the belt. Engine temp shot up and immediately shut off. Had belt replaced and water pump checked. All looked good.



Took boat out and the port Engine ran hotter that starboard side by about 20-30 degrees. Port Engine completely shut off at 180 degrees. Engine fired right back up but died again at 180 degrees.



First fix



Marine mechanic replaced fuel pump and both impellers. Took boat out and exact same thing happened. If boat temps on the port engine do not get to 180 it will run perfect. Running in cool water it’s great but still runs 170 ish. Summer water it will run until 180 (20 min) and shut off. Starboard runs at 145-155 in summer.



Nobody has an idea!!

Not sure why mechanic would’ve replaced fuel pump however I’d drain both both engines and keep an eye that all 4 drain about the same amount. Not sure where you boat or what you could’ve sucked up. Sea strainers??

Had you burned up an impeller as of recent that could be pieces of rubber caught up in your hoses, coolers etc?

See if you can swap wires in gauges easily to confirm it’s not a faulty gauge.

Water temps are one thing however oil temps would be more of a concern. Maybe buy a cheap auto store temp gauge kit even you you just zip tie somewhere where you can see it.

Just some thoughts and ideas

thermostat may be wrong or defective?

Mr. Murphy likes to get involved all the time. It's quite possible the shut-off at 180 is not related to the belt mishap.
​​But we likely think it is, when we get follow on symptoms from potential issue...often blinding us to the proper troubleshooting process.

Raw water cooled? What level of flow is there on the water discharge?
​
An IR heat gun is a great diagnosing tool...and can be had relatively cheap...even a Fluke.

You have an example engine running to compare temps on the cooling water pathway and affected metallic parts.

Is the EFI computer shutting the engine down for heat? What parameters will that get triggered?

Have you had your heat exchanger checked?

No pro here but i doubt an engine would die at 180

i would also consider an electric or electronic part that stop working when getting hot, as simple as a coil up to a computer

good thing as mentionned, you can swap parts with other engine till the problem switches to the other engine! Then you will know

If you have a loose connection or ground...something like that...temp level can have a factor with expansion. All it needs is the voltage to the computer to flicker...and it will kill the engine.

An overheating situation could have made this 'change'.

did you change the thermostat?