Smoke and run-on

brooster

Member

Equipment
B5200, BX2360, L3940, Z781i KW
May 15, 2021
68
8
8
Troy NC
I was putting up a privacy fence today and was moving the gates around with my tractor, a Kubota L3950 HSTG when all of sudden it revved up and started billowing white smoke. It would not cut off with the key, so I cut the fuel off at the filter and it finally quit. It was spewing oil out the exhaust, if it was turbocharged I would have thought that was it, but it’s not. Anyone got an idea of what has happened?
 

armylifer

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BX1860, FEL, RCK54P MMM, BB1548 Box Scraper, Quick Hitch, Piranha Bar, BX6315
Mar 26, 2013
1,955
695
113
Thurston County, WA
I was putting up a privacy fence today and was moving the gates around with my tractor, a Kubota L3950 HSTG when all of sudden it revved up and started billowing white smoke. It would not cut off with the key, so I cut the fuel off at the filter and it finally quit. It was spewing oil out the exhaust, if it was turbocharged I would have thought that was it, but it’s not. Anyone got an idea of what has happened?
It sounds to me like you have a blown head gasket. The other less common cause for an engine that is warm to have that happen is a cracked piston ring or even a hole in one of the pistons. It sounds to me though that you have likely blown a head gasket. Is there a sweet smell in the white smoke? If so, that is a sure sign that coolent is getting into the combustion chamber.
 
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lugbolt

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Equipment
ZG127S-54
Oct 15, 2015
4,807
1,575
113
Mid, South, USA
check the oil. If overfull sniff it for fuel. If it smells of fuel the lift pump is leaking into the crankcase.
 
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brooster

Member

Equipment
B5200, BX2360, L3940, Z781i KW
May 15, 2021
68
8
8
Troy NC
I appreciate all the advice, as soon as the weather clears I guess I’ll start looking into it!
 

brooster

Member

Equipment
B5200, BX2360, L3940, Z781i KW
May 15, 2021
68
8
8
Troy NC
check the oil. If overfull sniff it for fuel. If it smells of fuel the lift pump is leaking into the crankcase.
Yes crankcase is way over full and yes it smells of diesel. Ordered new pump, hopefully this will fix the problem, will changing the oil once be enough or is this something that should be done twice to make sure no fuel is left in the oil?
 
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lugbolt

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ZG127S-54
Oct 15, 2015
4,807
1,575
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Mid, South, USA
Yes crankcase is way over full and yes it smells of diesel. Ordered new pump, hopefully this will fix the problem, will changing the oil once be enough or is this something that should be done twice to make sure no fuel is left in the oil?
one oil change is probably sufficient. Change it, run it a little, then re-sniff. If it's still stinking like fuel, change it a second time
 

lmichael

Active member

Equipment
Kubota G2160
Apr 23, 2021
520
205
43
Rockford IL area
I am having a hard time figuring how a little lift pump can push fuel so hard as to get past the injector pump and into the crankcase. Am I missing something?
 

Fordtech86

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L3200
Aug 7, 2018
4,705
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Pineville,LA
I am having a hard time figuring how a little lift pump can push fuel so hard as to get past the injector pump and into the crankcase. Am I missing something?
The lift pump leaks fuels into the crankcase, causing oil level to increase, once it gets full enough it can start pulling the oil/fuel through the crankcase vent into the intake and start running away.
 
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lmichael

Active member

Equipment
Kubota G2160
Apr 23, 2021
520
205
43
Rockford IL area
I still don't get it. My lift pump is VERY low pressure. It only sends fuel to the injector pump. I just don't see enough pressure to push past the injection pump. But, I am looking at a little electric pump on mine near the tank. Not sure what there is on a larger model machine
 

Fordtech86

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L3200
Aug 7, 2018
4,705
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Pineville,LA
I still don't get it. My lift pump is VERY low pressure. It only sends fuel to the injector pump. I just don't see enough pressure to push past the injection pump. But, I am looking at a little electric pump on mine near the tank. Not sure what there is on a larger model machine
5B13DD14-5ED9-4022-8C8B-93A2DF6B7FAE.jpeg

Mechanical lift pump mounted on the block, runs off the fuel cam, they can leak fuel into the crankcase.
 
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Russell King

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L185F, Modern Ag Competitor 4’ shredder, Rhino tiller, rear dirt scoop
Jun 17, 2012
4,603
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Austin, Texas
On the mechanical driven pump some diaphragm tears and the fuel just leaks into the crankcase. On electrical ones I don’t see it happening either.
No code has to be inserted here.
 
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Mark_BX25D

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Bx25D
Jul 19, 2020
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Virginia
Mechanical lift pump mounted on the block, runs off the fuel cam, they can leak fuel into the crankcase.

Most older cars & trucks are exactly like this. It's a common problem when that diaphragm gets old. They get brittle, they leak, and into the crankcase is the only place that fuel can go. It's a direct path once that diaphragm is breached. Even a pinhole will do it.
 
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lmichael

Active member

Equipment
Kubota G2160
Apr 23, 2021
520
205
43
Rockford IL area
Most older cars & trucks are exactly like this. It's a common problem when that diaphragm gets old. They get brittle, they leak, and into the crankcase is the only place that fuel can go. It's a direct path once that diaphragm is breached. Even a pinhole will do it.
Yeah, the other diagram explained it. I remember my old wrenching days. Mechanical fuel pumps. Gasoline getting into the oil and such. I quit dealership wrenching way back in the early 70s.