How to Test an Outboard Motor’s Stator
When problems with an outboard’s charging system arise, one of the components to test for diagnosing the issue is the stator.
Watch the video above and read on below to learn how to do two basic voltage tests for an outboard motor’s stator.
NOTE: We tested the stator on a Honda BF40D outboard motor, but these tests may be done for similar outboards.
Outboard Stator Static Test - Engine Off
Remove the cowling of the outboard to begin a static or resting test. Using a digital multimeter, you’ll be measuring resistance in ohms across the three coils that comprise the stator.
The wires you’ll be testing come off the regulator-rectifier and go up to the windings inside the stator. The coils are known as Y1, Y2, and Y3 (or simply 1, 2 and 3).
When doing the resistance test, use the leads on the digital multimeter to get measurements from coils Y1 to Y2, then Y2 to Y3, and then Y3 to Y1. The resistance to check for on this particular model is between .25 and .37 ohms, and a high-quality multimeter is required to get those readings.
When taking voltage measurements, find the zero point and then subtract that number from whatever readings you come up with. Measuring something in that narrow of a window with an ohm meter isn’t easy, so put your multimeter’s leads together and find the natural position for what you’ll need to subtract away from the final reading.
In our Honda outboard’s case, the reading when putting the leads together bounces between 0.1 and 0.2, which means whatever measurements we get, we're going to subtract 0.1 from it for a final reading.
NOTE: The static stator test isn’t the best test in terms of accuracy, but it’s the one specified in the manual for our Honda outboard engine to test its stator.
For a coil that's damaged, you’ll typically see either an open circuit or a completely closed circuit. So if it’s completely burnt out, the reading will be the same as touching the leads together.
Start by testing circuits Y1 to Y2 with the leads on the multimeter, then from Y2 to Y3 and then Y1 to Y3. We got a 0.5 reading all three times, and we subtract a .1 from that for a .4 measurement, which means although the reading is a little high when compared to our 0.2 zero point, the stator in our Honda outboard is working.
Outboard Stator Live Test - Engine On
The more accurate stator test to do is a live test, in which you start the motor and then read the AC voltage from phase to phase (Y1,Y2, Y3). For this test, place the motor in a test water tank, then crank it up and take measurements on the multimeter’s AC setting.
The AC voltage we’re looking for on this test is somewhere between 18 to 20 volts, and up to 25 volts with motor running at idle.
Test the coils in the same way as the static test, plugging the multimeter’s leads from Y1 to Y2, Y2 to Y3 and Y1 to Y3. The readings that tell us our stator is working are within the established 18-20 volt range when testing from phase to phase, and above 25 volts at idle.
As mentioned above, these stator tests can be applied to other outboard makes and models. Check the manual for the model you’re testing to find out what readings you should be getting from the stator. If the readings or measurements aren’t within the specified range, the stator needs to be replaced.
The stator is just one of several electrical components that could be causing a no-start or no-charge condition on an outboard motor. Watch the video above for tips on how to troubleshoot an outboard motor that won’t start.