The Wire That Caused Years Worth Of Expenses
So I get called to winterize a new customers boat and it has already been hauled to their house and needs to be winterized on the hard. Not an issue, I do this all the time. Except on this 39F morning the Westerbeke motor does not want to start. I ring the owner and ask if their are any tricks to start this particular motor which he has not keyed me in on?
It is then I get the story about his glow plug solenoid failing over and over and over and that he’s replaced glow plugs too and perhaps that is the issue.
I also hear about how much money he has laid out over the years to try and solve this issue. I find his story odd because I too own a Westerbeke and the only time I had an issue with glow plugs was when I fried them using a Lithium battery bank which has a higher voltage than lead acid. I stupidly used my normal ten second push interval, which was fine for lead acid, but not for Lithium. Clearly my own fault.
I do know that Westerbeke solenoids are a rather cheap intermittent duty product but they should easily last more than a year. I take a look and yes he has brand new glow plugs and a brand new Cole Hersee heavy duty solenoid. At least the last tech put in a good solenoid… Time to investigate.
#1 I pull out my test leads and jump from the positive feed to the energizing coil of the solenoid. Sure enough I hear a loud click, as I should. This means it is working right? NO!!
What you can’t hear is the relay un-click because the circuit can’t pass enough current to hold the solenoid closed. It momentarily worked but immediately failed once the current tried to load up the circuit.
#2 I set my Fluke clamp meter to in-rush and clamped it around the glow plug feed wire. I then energized the coil with the positive test lead.. Sure enough I capture a transient spike of 19.6A. I then repeat the test with the in-rush turned off and I see a blip on the screen, then zero amps DC. The negative side of the circuit simply can’t pass current.
This little test tells me the solenoid is not staying closed when energized to do so. The test lead on the positive side is known good, so the solenoid should remain closed, but it won’t.
#3 The only other option, in this circuit, is the small 6″ ground wire from the relays coil to the engine ground. I slap a test lead on the coils negative side, and ground it to the engine block, to rule out the 6″ wire. I then repeat the test and the glow plugs stay energized. The solenoid works perfectly. Good glow plugs and a perfectly good solenoid.
#4 Diagnosis? Bad 6″ neg jumper wire from the coil to engine block. This is a simple $2.00 fix. Unfortunately this owner had spent in-excess of $1000.00 over the years “fixing” this problem.
So what’s the moral of the trouble shooting story?
NEVER, EVER, EVER ignore the negative side of the circuit when testing DC circuits. This test took all of about four minutes yet three or four solenoids later, a set of glow plugs, and LOTS of money wasted all because a 6″ wire could not pass current sufficiently and did so intermittently.
This is simply poor trouble shooting 101…