Pre-Heat Solenoid

[TBOT422]

I replaced the fuel filters this weekend and discovered that the pre-heat solenoid is not working AGAIN! I believe I have replaced this part about 5 or 6 times in the 7 years we have owned the boat. Does anyone have any ideas as to what might be causing it to fail? engine vibration? cheap component? I have learned that the solenoid is simply a starter solenoid for a Ford Car/Truck –SW3 – SNL135 and have been purchasing them on-line. Last spring I bought the Red 'Heavy Duty' version on e-bay for $8. It lasted 6 months. Maybe less, as there are no symptoms that the solenoid does not work until I need to fill a new fuel filter. The boat starts just fine almost instantly even when it is not working.

Any ideas would be appreciated. Maybe I should buy the Westerbeke part for $36?

[wolfe10]

Wow, an unusual failure, particularly multiple ones.

Scratching my head trying to figure out a cause-- low voltage to the signal terminal of the solenoid could certainly do that. It could be low enough (likely due to poor or corroded connections between battery, key and solenoid) to cause the solenoid to "chatter"/make and break. Switching under load would quickly pit the contacts, causing solenoid failure. So, next time you engage the solenoid, check voltage between the signal terminal and its ground.

Just a thought.

[TBOT422]

Brett,

Here is a little more background that may help. I first discovered the solenoid was not working immediately after we purchased the boat. At the time it was only 4 years old, and I assume that the solenoid had not been working for quite some time. It failed several times over the years, with no apparent sign of failure other than the fuel lift pump (and I assume the glow plugs) did not work with the key switch in the spring loaded 'pre-heat position'. Last spring while having some other service done, the service company apparently broke something inside the key switch so that the spring loaded function did not work properly. The boat would start and for a variety of reasons I decided to take it back to our home dock. After a couple of hours motoring home, I lost all power to the helm, and discovered the pre-heat solenoid was blown (black goo oozing out and the smell of burning electrical). I learned that when it blew, it tripped the main 20-amp breaker that caused all the helm power to go away. This was a different sort of failure than the usual solenoid failure, and I assumed it was due to the fact that the ignition switch may have been in the pre-heat position for 2 hours as the spring loaded function was broken. I assumed the continuous load in this case caused the solenoid to blow. I replaced the key switch and solenoid and all was fine for 6 months or so until I found out that the solenoid was not firing the fuel lift pump after changing the fuel filter over the weekend.

I want to be clear that I understand what you are saying. My understanding is that this solenoid only functions when the key switch is placed in the spring loaded pre-heat position, correct? So when you say "engage the solenoid" you mean key switch in the pre-heat position? I will check voltage at the signal terminal with the key in the off, on, and pre-heat positions and see what I've got. I hate electrical problems!

Thanks for the thoughts

[wolfe10]

Gary said, "I want to be clear that I understand what you are saying. My understanding is that this solenoid only functions when the key switch is placed in the spring loaded pre-heat position, correct? So when you say "engage the solenoid" you mean key switch in the pre-heat position? I will check voltage at the signal terminal with the key in the off, on, and pre-heat positions and see what I've got. I hate electrical problems."

Yes, the solenoid is only engaged when the key is in the spring loaded pre-heat position. So, that is when the solenoid signal terminal should have full battery voltage.

Sounds like different failure causes from solenoid energized for 2 hours. Hadn't thought of that failure mode, but that would certainly kill it as it is a momentary not constant duty solenoid. I am surprised that the glow plugs did not burn out staying on for 2 hours, and with the engine running. I would sure check them.

[TBOT422]

Brett,
Here is what I see. I have 12.4 volts at the main terminal of the solenoid with the ignition switch in off. No voltage at any other terminals. I have continuity across the small 10 amp breaker and about 10 ohms resistance across the small resistor wire from the 10 amp breaker. When switching the key to the ON position I get about 9 volts on both sides of the 10 amp breaker which is connected to the I terminal of the solenoid. No voltage at the S terminal yet. When I turn the ignition switch to the pre-heat position I get 12.4 volts at the S terminal of the solenoid. No other voltage changes as this solenoid is bad. If good I should get 12 volts at both the I terminal, powering the fuel lift pump and the glow plug connection of the solenoid.
I believe that is how it is supposed to be. I really don't understand where the 9 volts come from, but I believe it comes from the oil pressure switch that is powered with the ignition in the ON position and the 10 ohm resistor to ground.

[wolfe10]

Sorry, I don't have access to the boat/wiring diagrams right now. It is offshore Carrabelle to Venice FL (my brother's turn to move it) for our Bahamas trip.

Once we see how far he gets before returning to Texas for Thanksgiving through Xmas, we will start looking for a place to keep it in South Florida for that 5-6 week period.

But, solenoids are pretty simple beasts-- two large lugs (one to battery, the other hot only when the solenoid energized).
Either one or two small signal terminals. If one, it is the HOT from the ignition switch and ground is through the body of the solenoid. If two, the second is to external ground. Agree, if 12 VDC to small signal terminal and ground good, but no voltage at the other large lug, the solenoid is BAD. A quick source of 12 VDC positive for the signal terminal is a short wire from the large lug connected to the battery. Small gauge is fine, as you are only going to draw an amp or two to "activate"/close the solenoid.

Brett

[TBOT422]

I found a 'marine' grade solenoid on ebay for $8.30. I think I will try it and see if it lasts any longer.
https://www.ebay.com/itm/New-Ford-Start ... 0677.m4598

Hey, this one is Blue and matches the bimini so maybe that's a good sign!

[jbd3]

Just to add my 2 cents, consider your ground. I solved a weak and intermittent buzzer problem with a strong supplemental ground circuit and I was prefectly happy until I discovered a lightning hit the other day which rendered my engine and several engine related instruments inoperable. I was living with the start relay position of the key tripping the 20 amp breaker but it wasn't crucial in south Florida so I was just postponing troubleshooting it. More after we get the repairs initiated.

[bjtimm]

I just purchased a 2005 Catalina 350 and crossed the Gulf in the worst conditions I've been in in a small boat. 12-18' seas and gale force winds. She handled it perfectly and I am in love with this boat.
However, now in Kemah, TX and notice that the lift pump runs constantly and the glow plugs are always on.
Also tonight, buttoning her up I noticed the plotter on despite that all the DC switches were off.
Any advice, suggestions, ideas, would be much appreciated.
Bart

[scott.monroe]

Hi Bart,

Are the glow plugs really on? Don't run it long like that they will burn out (expensive replacement). You can verify if they are on with a volt meter positive on the tip of the glow plug, ground from a clean metal part on the engine block. If they are indeed on then.

Given that the key switch is driving the power to the plugs you might want to start there. Could imagine it getting beat up pretty good and failing (but failing on is unusual but shorts do happen). Next step is the switch in the pedestal sends power to the solenoid on the engine block that in turn sends power to the bank of glow plugs. That could get seized internally in the on position. Light taps with a hammer might free up the internal disk. If that works, would definitely replace the solenoid.

Regarding the plotter? That is weird. If you're new to the boat you might want to look and make sure that switch is servicing the plotter circuitry. Not unheard of to add a new power source for electronics (if electronics are tied to engine starting batteries the voltage drop during engine start up mucks with voltage sensitive electronics at times).

Just thoughts,
Scott

[bjtimm]

Thanks for the reply, it turns out the solenoid was bad. Replaced it and all is well.