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Old 05-02-2016, 10:04 AM   #1
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Kubota engine on Phasor genset wants pre-heat

I have a 6.5 KW Phasor generator with about 300 hours on it. The motor is a 3-cylinder Kubota D905. Location is the Caribbean, so ambient temperature is always above 80F.

Two weeks ago I tried to start the generator after 6 months of not using it. It swung easily, but with no signs of life. Previously it had always started first push of the button and never required pre-heat. In fact, I had concluded that the pre-heat was disabled because there was no solenoid "clonk" when the heater switch was pressed - turns out there is no solenoid; the current for the heaters passes directly though the toggle switch!

I replaced both fuel filters, cleaned the strainer in the lift pump and bled the whole system. This particular motor requires 12 volts to run. I temporarily removed the stop-solenoid (technically a run-solenoid) which takes all the normal culprits like oil pressure and coolant temp switches etc out of the equation. Nothing! The stop-solenoid pushes on a lever in the injector pump to stop the engine. I checked that this lever was free to move and was in the "run" position. Nothing!

As a last resort I tried about 5 seconds of pre-heat and Voila! it started and ran. This is repeatable: the engine now requires pre-heat to start from cold, and re-starts easily without it when hot.

The need for pre-heat is not an inconvenience and, I am told, is common on small Kubotas.
The question is: What has changed and should I be concerned?
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Old 05-02-2016, 10:32 AM   #2
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By preheat, I assume you mean glow plugs. You are in the Caribbean, so do you run the genset 24/7 to power the A/C? If so you may have glazed cylinders which lowers compression and causes hard starting.


The glazed cylinders, if that is the problem, are caused by severe under loading at night when the A/C cycles on very little.


You can try running very hard for a day, which is what Tony Athens over at boatdiesel says can cure some glazed cylinder gensets. Set up enough load to bring it up to about 5 KW. That will take at least three 1,500 watt space heaters running on high. You will need to find three outlets on separate breakers to do this. Run for 8 hours, let the engine cool down overnight and see how it starts.


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Old 05-02-2016, 11:07 AM   #3
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Could it be that the fuel shutoff function is locked in the shutdown mode?
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Old 05-02-2016, 11:18 AM   #4
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Could it be that the fuel shutoff function is locked in the shutdown mode?
Eric may be close. Can't speak for phasers, but on many gensets the pre heat function is part of an energizing starting sequence, fuel pump included. Six months down - humm. What does the book say for starting instructions. Maybe there is no problem.
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Old 05-02-2016, 11:57 AM   #5
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Crank speed can make a huge difference on whether a Kubota needs glow or not. Also ambient temp. Most do need a bit of glow even in Caribe temps.

Your battery is probably not as hot as it was 6mo ago.

Don't worry about it, just give it a glow if it wants it. Keep an eye out for smoking or oil use. Can also check oil fill cap or crankcase vent hose for blowby.

And next time don't leave it for so long. Would a girlfriend warm right up to you if you ignored her for six months?? Feelings have been hurt!!
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Old 05-02-2016, 12:58 PM   #6
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Eric may be close. Can't speak for phasers, but on many gensets the pre heat function is part of an energizing starting sequence...
This is certainly true of my Northern Lights generator.

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Old 05-02-2016, 03:46 PM   #7
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Ski

Do you know on a Phasor how the electric fuel pump is sequenced/energized?
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Old 05-02-2016, 04:07 PM   #8
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This is certainly true of my Northern Lights generator.

Ken
Same here........
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Old 05-02-2016, 04:21 PM   #9
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SkiinNC: I tried that after about 5 years and yes, the starting sequence did change considerably. Not only did the start up require additional glow brought about by more expensive wine it involved a blue pill on my part to get things running again. I don't know anything about starting generators though.
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Old 05-02-2016, 04:49 PM   #10
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ulysses- Ha!

Sunchaser- No, never had to go through their wiring. Usually fuel solenoid is pulled in either by preheat switch like NL, or by start circuit. Then when running it goes through shutdown switches either directly or through a relay.

If you have a schematic, post it.

So is solenoid not pulling in for a start? Might be related to the GP's not working.
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Old 05-02-2016, 06:15 PM   #11
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Thanks all.

Ski: that is the best piece of advice I have received for some time. The most reassuring too.

For those who asked, or are curious, the following applies to the 6.5 Phasor. I can't speak for the other versions, but they could be similar.

The "Run" switch supplies power to the electric fuel pump (Facet pump in my pic).

The "Run" switch also supplies power to the Pre-heat switch.

The "Start" switch, when pressed, supplies power to the fuel solenoid.
This moves the plunger to the run position.

When the engine starts, the solenoid receives power from a secondary circuit to hold the plunger in the run position.

The plunger on the fuel solenoid is pushed out by a spring when the solenoid is not getting power. This is the fuel-off position. When the solenoid gets power, it pulls the plunger in and the fuel flows.

The fuel system on my main engines are the other way round: they need power to stop rather than power to run. This is nice because a failure in the 12-volt system does not leave you without propulsion when miles from land. I wish the generator was the same.
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Old 05-02-2016, 06:22 PM   #12
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It's good for gennies to shut down with lack of power or other fault. Gennies are not mission critical or otherwise safety related so if they poop to protect themselves, better yet.

Main engines, different. I might chose to cook it should it overheat going into a snotty inlet. Otherwise lose the whole boat, or me.
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Old 05-02-2016, 07:01 PM   #13
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The other thought process that may have been involved in that design might be that the generator running should be producing 12v through the alt. or powering the house battery chargers and this should always be available if the generator portion of the unit is working.
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Old 05-05-2016, 01:19 PM   #14
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ANY engine built with "pre combustion" chambers will require pre heat to start promptly even in the tropics.

Once warm they will usually fire off with out the heat.

Pre combustion chambers is chosen for better fuel economy and less diesel rattle underway.

An OK compromise of complexity for the advantages.
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Old 05-05-2016, 03:44 PM   #15
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FF,
Yes.
I always start my Mitsu w glow. It has a pre- chamber. And is quieter than my last boat w direct injection. My glow heaters are over 10 yrs old and work well. I pulled one out once to see how hot it gets. Got red hot in several seconds. I "glow" for less than 10 seconds per the book.
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Old 05-05-2016, 04:03 PM   #16
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Glow plug diesels are chosen over direct injection for a couple reasons: Quieter combustion, better cold starting, capable of higher revs.

But they are not more efficient. A good bit of heat is lost to the combustion chamber, and there is some throttling too, both hurt efficiency a bit. But since most of these engines are small, a 5-10% hit on burn rate is not the end of the world.

I had a VW rabbit 1.6liter, car weighed about 2000lb. Glow plug engine. At 65mph it got 40-45mpg. Now have a 2liter jetta, 2960lb. Direct injection. At 75mph, it gets 45-50mpg.

The modern direct injection engines use computer control of injection to get rid of most of the normal diesel knock. So really no reason for prechamber engines unless you want to stay mechanical and quiet.
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Old 05-05-2016, 08:00 PM   #17
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And if you dont mind the "prechambers" getting loose and busting a piston. Oh wait,,, did Volvo have a patent on that. No, they all did it.
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Old 05-07-2016, 09:08 AM   #18
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Quote:
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ANY engine built with "pre combustion" chambers will require pre heat to start promptly even in the tropics. Once warm they will usually fire off with out the heat.
FF: Interesting statements (and I am in the tropics).

i) Does my little Kubota D905 (in the OP) have precombustion chambers?

ii) Even if it does, why did it start from cold every time without pre-heat and now requires it?


.
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Old 05-07-2016, 09:48 AM   #19
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One answer to that question could be the fuel. Diesel fuel has a flash point of anywhere between 52 to 96 C. Perhaps you took on some lower flash point diesel.
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Old 05-07-2016, 10:24 AM   #20
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Originally Posted by Shoalwaters View Post
FF: Interesting statements (and I am in the tropics).

i) Does my little Kubota D905 (in the OP) have precombustion chambers?

ii) Even if it does, why did it start from cold every time without pre-heat and now requires it?


.
But it starts OK if you use the factory installed glow plugs switch?
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