I have a 1968 Kubota L285 diesel tractor, my question is the tractor is a little hard to start even in the summer, it runs good once it starts. I checked the glow plugs and the manual says they should read 1.5 ohms. Mine each read 2.2 ohms. Does that make any difference in the glow plugs working properly. I also thought maybe the injectors were dirty and was wondering if I should put something in the fuel to help clean them. Thanks for any response.
- Thread starter gyroman
- Start date
Bob M
Well-known Member
If it runs well once it starts, it's most certainly a glow plug problem.
The higher the resistance of a glow plug the less it heats up. A fresh set of glow plugs should solve your starting problem. While you are at it check the glow plug wiring and solenoid for corroded terminals, etc and repair as necessary.
The higher the resistance of a glow plug the less it heats up. A fresh set of glow plugs should solve your starting problem. While you are at it check the glow plug wiring and solenoid for corroded terminals, etc and repair as necessary.
D Nickerson
Member
Yes, as said replace glow plugs. Kubotas are especially finicky with
start up. At least all the ones we have anyway. I call them fair weather
engines. Even in the summer time you have to hang on the glow plugs for
15-30 seconds depending what model you have. It's important to keep them
up to date, as your starter will work harder and fail sooner.
start up. At least all the ones we have anyway. I call them fair weather
engines. Even in the summer time you have to hang on the glow plugs for
15-30 seconds depending what model you have. It's important to keep them
up to date, as your starter will work harder and fail sooner.
Steve in VA
Well-known Member
- Location
- Natural Bridge Virginia
Are your sure about the relationship between resistance and heating up? I'm thinking that for a glow plug or wire, the higher resistance would generate more heat.
I agree with the glow plug diagnosis.
I agree with the glow plug diagnosis.
Steve in VA
Well-known Member
- Location
- Natural Bridge Virginia
This may help and at the very least is a good 'bit by the dumb-a$$ bug' story.
My Cat 301.5 mini was hard to start but ran like a champ once running. So, I decide it must be glow plugs and check them with the VOM. All 3 tested within range. Problem was, I neglected to realize that there was a single hot lead bridging all 3 plugs and I didn't isolate each plug when tested!! So after a few dope-slaps I isolated the plugs and sure enough, 1 of 3 bad. Any chance you've fallen into the same hole?
My Cat 301.5 mini was hard to start but ran like a champ once running. So, I decide it must be glow plugs and check them with the VOM. All 3 tested within range. Problem was, I neglected to realize that there was a single hot lead bridging all 3 plugs and I didn't isolate each plug when tested!! So after a few dope-slaps I isolated the plugs and sure enough, 1 of 3 bad. Any chance you've fallen into the same hole?
Tx Jim
Well-known Member
- Location
- Coyote Flats, Texas
Hard cold starting on older Kubota engines may be a fact BUT my '11 M7040 starts very easily in Texas winter temp's.
Bob M
Well-known Member
Am I sure? Absolutely!
Why? The more watts passing thru a glow plug, the hotter it will get.
A mathematical explanation:
Rearranging with Ohm's law (E = I x R; where E is volts, I is current and R is resistance) you get I = E/R. And the heat released (watts) thru a resistance is I squared x R
Now assuming a 12 volt supply and 1.2 ohm glow plugs, a good plug will draw 12 / 1.2 = 10 amps. And (10)squared x 1.2 = 120 watts of heat released
But a 2.2 ohm plug will draw only 12 / 2.2 = 5.5 amps. And 5.5(squared) x 2.2 = 66 watts.
Bottom line is a worn, 2.2 ohm resistance plug will consume only about half the wattage of new plug. So it will heat up considerably less.
----
Incidentally my experience with older Kubotas is they indeed need good glow plugs (also a good battery!) to start reliably, even in warmer weather.
Why? The more watts passing thru a glow plug, the hotter it will get.
A mathematical explanation:
Rearranging with Ohm's law (E = I x R; where E is volts, I is current and R is resistance) you get I = E/R. And the heat released (watts) thru a resistance is I squared x R
Now assuming a 12 volt supply and 1.2 ohm glow plugs, a good plug will draw 12 / 1.2 = 10 amps. And (10)squared x 1.2 = 120 watts of heat released
But a 2.2 ohm plug will draw only 12 / 2.2 = 5.5 amps. And 5.5(squared) x 2.2 = 66 watts.
Bottom line is a worn, 2.2 ohm resistance plug will consume only about half the wattage of new plug. So it will heat up considerably less.
----
Incidentally my experience with older Kubotas is they indeed need good glow plugs (also a good battery!) to start reliably, even in warmer weather.
Zeke Boniface
Member
I would probably buy one glow plug and test it with my meter before I bought the other three. But sometimes it takes me forever to fix things.
Zeke B.
Zeke B.
Ken Macfarlane
Well-known Member
Both my newer Kubotas (1999 and a 2003) start without glow plugs to well below freezing but these guys know their stuff on older models.
The resistance of a glow plug is dependent on temperature. Does the manual state at what temperature that spec is for? When did you measure resistance, engine hot/warm, temp outside? The hotter it is (ambient or engine temp) the more resistance it will have. Since all plugs measure 2.2ohms I doubt the plugs are the problem.
Understanding how a glow plug is made and works, 1.5 and 2.2 ohms is not a significant difference. Incidentally you can also get a good idea on a cylinder that is weak or misfiring by measuring glow plug resistance on a warm running engine. The glow plug with a lower resistance is weak or misfiring cylinder.
Understanding how a glow plug is made and works, 1.5 and 2.2 ohms is not a significant difference. Incidentally you can also get a good idea on a cylinder that is weak or misfiring by measuring glow plug resistance on a warm running engine. The glow plug with a lower resistance is weak or misfiring cylinder.
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