On the EX, EX Sport, EX Deluxe and EX Limited from 2017 on, owners describe a pattern: a long ride, the temperature warning and the beep, then reduced power. In calm water it rarely happens. The engine is the three-cylinder 1049 cc TR-1, which is common to all EX trims.
What the manual says
The EX manual says the overtemperature warning and the oil pressure warning share a tone, and both reduce engine speed automatically. As a remedy it lists cleaning the intake and letting the engine cool. It is a short instruction, but note which part comes first: the manual points at the intake before any electrical part.
What owners find
Reports from owners of EX, VX, FX SVHO and FZR boats are consistent. The cause is usually a problem with how water moves, and only after that a sensor. The usual candidates:
- cavitation at the pump, which happens when the impeller draws air instead of water
- a foreign object in the intake grate
- an impeller with chipped blades
- a plugged small cooling-water passage
- exhaust passages that closed up after poor flushing
That the problem shows on long rides and hardly in calm water makes some people suspect cavitation. It is a guess that fits the pattern, and not something anyone has proven for every case.
The list is ordered roughly by how little each check costs, and it is worth following that order. Pulling a grate takes minutes.
One check that people use: run the engine with a water supply and look for water leaving at the rear and at the test tube at the front. Water at the rear only suggests the path is closed somewhere. It is a simple test and it points you at plumbing before you buy a sensor.
What recording a curve adds
To find out whether you have a flow problem or a sensor problem, record the ride. The M-JET Diagnostic supports all EX variants and its data logger records the temperature values together with engine speed and throttle position during a test ride. After the ride, look at the shape:
A temperature that rises steadily under sustained load and falls slowly when you ease off tells you the engine is struggling to shed heat, so the water path comes first. A temperature that jumps in steps or reads something implausible points to the sensor or its connector. The temperature codes to look for are 15 (engine temperature) and 65 (exhaust manifold water temperature), though the numbers can differ by control unit and source, so rely on the app's description.
Note the engine speed alongside the temperature. If the boat drops speed at the same moment the warning appears, you are looking at the speed reduction the manual describes, and not at a separate fault.
Where the scan stops
Cavitation, a worn impeller, debris in the intake and blocked cooling passages leave no code. The app can show that the engine got hot and when, which saves you from replacing a sensor that was reading honestly. It cannot tell you why.
My order would be: pull the intake grate and look, check the impeller, confirm water at the outlet, and only then think about sensors. More on the sensor side is on the overheating and temperature sensor page, and the model overview is on the EX diagnostics page.
