BX25 loses power after engine warms up

timpursell

New member

Equipment
Kubota BX25-DLB
Jun 9, 2021
10
1
3
Clayton, NC
Let me acknowledge right off the bat that I know this issue has been presented and discussed numerous times on this forum, but I am really stumped with a problem right now and would appreciate any additional insights anyone could provide.

Problem

The engine on my 2013 Kubota BX25-DLB starts to lose power after the tractor has been in operation about 20-30 minutes. With the mower deck engaged, the engine struggles to maintain 2,500 rpms (normal idle ~3500). If I'm mowing AND going up a hill, it almost stalls. If I let it cool down for awhile, it will work just fine for another 20 or 30 minutes.

Background

This problem started to occur after I [mistakenly] used some bad fuel.

Steps taken to date


  1. Assuming this problem was related to the fuel issue, that is where I focused first.
    • Drained the fuel tank
    • Replaced all of the filters
    • Refilled tank with fresh diesel
  2. The problem persisted, so I continued focusing on fuel delivery as a possible culprit.
    • Installed a filter relocation kit
    • Replaced the 2nd filter with a new one (again)
    • Upgraded the electric lift pump with an after market replacement
    • Measured fuel pressure at the injection pump (~7 lbs) and made absolutely sure the fuel supply was not an issue
  3. Still no luck, so I tried some more things.
    • Replaced the air filter (just in case)
    • Pulled all of the injectors, took them apart, cleaned, and reassembled them
    • Reinstalled injectors with fresh crush washers
    • Bled the injector pump
    • Reinstalled the fuel rail
    • Manually bled the fuel lines (that took a LONG time, btw)
BUT, I am still having the same issue. Just tried to mow the lawn earlier this evening and could barely get it back to the garage after mowing less than an acre.

If anyone has any ideas, I would appreciate any insights or suggestions.


Thanks!!!
 

Fordtech86

Well-known member
Lifetime Member

Equipment
L3200,la525,LP 5’bushhog,LP 5’disc,LP boxblade,2bottom plow,40 gal sprayer
Aug 7, 2018
1,852
519
113
Pineville,LA
You have done a lot, but I didn’t see where you have cleaned the fuel tank. I would suspect something in the tank floating around and blocking the outlet after running. Grass,leaves, additive cap seals, rust from fuel sender, etc. let it sit and it moves away, start run repeat.
 
  • Like
Reactions: 1 user

85Hokie

Well-known member
Lifetime Member

Equipment
BX-25D w/ Filled Rears,2" Spacers,PTB. Under Armor, 90'-90'-92'-B7100HST's
Jul 13, 2013
8,192
506
113
Bedford - VA
The one item I do NOT see and I have never seen as a problem but WOULD and could be yours.......

restricted fuel cap!
 
  • Like
Reactions: 1 user

Mark_BX25D

Active member

Equipment
Bx25D
Jul 19, 2020
223
104
43
Virginia
What the two previous guys said, and if that doesn't help...

Back to basics. Check your compression. Cold and warm.

Not a likely scenario, I recognize, but it's always good to check the basics. Then you know.
 

Russell King

Well-known member

Equipment
L185F, Modern Ag Competitor 4’ shredder, Rhino tiller, rear dirt scoop
Jun 17, 2012
2,532
181
63
Austin, Texas
Clean outside of radiator and any screen in front of the radiator?

Do you have any idea what the temperature of the engine is when it starts to run badly?
 

kubotafreak

Active member

Equipment
GRAND l6060, L3560, B6100, gr2100, tg 1860, g1800, g1900, g2160
Sep 20, 2018
401
93
28
Arkansas, US
I would do a compression check next. Can eliminate, or shed light on a potential problem. Also check the hydraulic fluid.
 

timpursell

New member

Equipment
Kubota BX25-DLB
Jun 9, 2021
10
1
3
Clayton, NC
You have done a lot, but I didn’t see where you have cleaned the fuel tank. I would suspect something in the tank floating around and blocking the outlet after running. Grass,leaves, additive cap seals, rust from fuel sender, etc. let it sit and it moves away, start run repeat.
Sorry, should have mentioned that. I actually filled up the tank with a degreaser and cleaned it out real good. Fuel seems to flow quite well. At one point in my troubleshooting, I even had the lift pump pull fuel directly out of a can to eliminate the fuel tank as a cause, but it didn't help. (It was a little difficult driving around with an open fuel container on the floor board, too :))

At one point I put a fuel pressure gauge inline and made sure the pressure wasn't dropping. I realize that doesn't equate to flow, but it was at least an indicator.

Question - now that I have a "real" fuel filter with a transparent bowl, would I be able to see any evidence of a fuel flow problem?
 

timpursell

New member

Equipment
Kubota BX25-DLB
Jun 9, 2021
10
1
3
Clayton, NC
Clean outside of radiator and any screen in front of the radiator?

Do you have any idea what the temperature of the engine is when it starts to run badly?
I actually clean the radiator and screen almost every time I am done mowing (it really sucks the loose grass in there. ) The gauge isn't showing any higher temperature than I was experiencing before the current problems. The engine warms up fully within 5-10 minutes, but the problem doesn't start occurring until 20+ minutes, and the engine doesn't see to be any warmer at that point.
 

timpursell

New member

Equipment
Kubota BX25-DLB
Jun 9, 2021
10
1
3
Clayton, NC
The one item I do NOT see and I have never seen as a problem but WOULD and could be yours.......

restricted fuel cap!
So I tried loosening the cap to make sure air was getting in and that didn't help. At one point in my troubleshooting, I even rerouted the fuel line to pull diesel directly from an open can to eliminate issues with the fuel tank altogether. I've tried really hard to follow all of the guidance I saw in other posts, but so far to no avail...
 

timpursell

New member

Equipment
Kubota BX25-DLB
Jun 9, 2021
10
1
3
Clayton, NC
I would do a compression check next. Can eliminate, or shed light on a potential problem. Also check the hydraulic fluid.
I actually flushed and replaced the hydraulic fluid as well. Mostly because it was time to do so (500 hours on the meter), but in some part because someone mentioned that in another post as an idea.

Sounds like my next tool for the box will be a compression tester! I have one for regular four-stroke engines, but not diesel.
 

timpursell

New member

Equipment
Kubota BX25-DLB
Jun 9, 2021
10
1
3
Clayton, NC
What the two previous guys said, and if that doesn't help...

Back to basics. Check your compression. Cold and warm.

Not a likely scenario, I recognize, but it's always good to check the basics. Then you know.
I'm with you. I like actually knowing stuff rather than guessing! So far everything I know hasn't helped resolve the issue, so by definition there is still something I don't know... :unsure:
 
  • Like
Reactions: 1 user

802Driver

Active member

Equipment
LX2610SU 60" Bucket Land Pride54" Box Blade Farm King 4572 Rear Blade
May 18, 2020
119
79
28
Manitoba, Canada
It would seem like your down to a compression test, "final answer? final answer Bob..." lol . You have been more than thorough, not a whole lot left to check now.
 

Henro

Well-known member

Equipment
B2910, BX2200, KX41-2V mini Ex.
May 24, 2019
1,521
420
83
North of Pittsburgh PA
Has the valve lash ever been checked?
Also, do not get over enthusiastic putting oil in the cylinders when you do the compression check.

No personal experience, but I have read warnings here on OTT that when using oil during a compression check, if too much is put in a diesel engine cylinder, after things are put back together there is a risk of hydro-locking and $$$ damage.
 
  • Like
Reactions: 1 user

aaluck

Active member

Equipment
L4400HST, Bush Hog 276, RDTH60, Speeco PHD, etc
Oct 9, 2019
374
174
43
Snowdoun, AL
A while back I posted for a friend that had a Deere with this exact problem... although his tractor was made in 1967. Could be your issue.

Anyway after replacing the fuel lines, doing pretty much everything you have done he hauled it to the dealer. Tank was rusted and particles were blocking the fuel line. Replaced tank and good as new--from 1967.
 

timpursell

New member

Equipment
Kubota BX25-DLB
Jun 9, 2021
10
1
3
Clayton, NC
Has the valve lash ever been checked?
Interesting thought. That is one thing I have not checked. Could that cause the symptoms I am experiencing as the engine parts warm up? Will the gasket survive after removing the cover or should I get a new one to have on hand just in case?
 

timpursell

New member

Equipment
Kubota BX25-DLB
Jun 9, 2021
10
1
3
Clayton, NC
A while back I posted for a friend that had a Deere with this exact problem... although his tractor was made in 1967. Could be your issue.

Anyway after replacing the fuel lines, doing pretty much everything you have done he hauled it to the dealer. Tank was rusted and particles were blocking the fuel line. Replaced tank and good as new--from 1967.
Great thought. I tried to eliminate the tank as the culprit by rerouting a line to pull directly from an open container of fuel and had the same problem. It really does seem like a simple fuel flow issue which is why I focused so much on that up front. This mystery is driving me crazy at this point... 😠
 

85Hokie

Well-known member
Lifetime Member

Equipment
BX-25D w/ Filled Rears,2" Spacers,PTB. Under Armor, 90'-90'-92'-B7100HST's
Jul 13, 2013
8,192
506
113
Bedford - VA
A while back I posted for a friend that had a Deere with this exact problem... although his tractor was made in 1967. Could be your issue.

Anyway after replacing the fuel lines, doing pretty much everything you have done he hauled it to the dealer. Tank was rusted and particles were blocking the fuel line. Replaced tank and good as new--from 1967.

He did bypass the tank in post #9 ......... I was thinking the same thing (not tank rust - but rather fuel sending unit rusting and breaking down)
 

Henro

Well-known member

Equipment
B2910, BX2200, KX41-2V mini Ex.
May 24, 2019
1,521
420
83
North of Pittsburgh PA
Interesting thought. That is one thing I have not checked. Could that cause the symptoms I am experiencing as the engine parts warm up? Will the gasket survive after removing the cover or should I get a new one to have on hand just in case?
My understanding is that over time, as the valves wear and seat in more, eventually the clearance goes to zero, and you end up with a burnt valve if no action is taken. When the adjustment clearance goes to zero, you will start to lose compression because the valve does not seal completely.

A poor seal at the valve means lower compression, and lower compression generally means hard starting. As things heat up they expand, which could mean you are at the end of the range for valve adjustment and if you do not act quickly you may end up with a burnt valve and more involved repairs.

I am not a mechanic...this is just my personal understanding and I am sure if I am off base someone better qualified with correct my thinking... :)
 
  • Like
Reactions: 1 users

timpursell

New member

Equipment
Kubota BX25-DLB
Jun 9, 2021
10
1
3
Clayton, NC
My understanding is that over time, as the valves wear and seat in more, eventually the clearance goes to zero, and you end up with a burnt valve if no action is taken. When the adjustment clearance goes to zero, you will start to lose compression because the valve does not seal completely.

A poor seal at the valve means lower compression, and lower compression generally means hard starting. As things heat up they expand, which could mean you are at the end of the range for valve adjustment and if you do not act quickly you may end up with a burnt valve and more involved repairs.

I am not a mechanic...this is just my personal understanding and I am sure if I am off base someone better qualified with correct my thinking... :)
Thanks to all for the great ideas. It's going to take me a few days to get some additional tools and try a few more things. I'll keep everyone posted on my progress. I know it is frustrating to see a thread like this that has no closure and just keeps everyone hanging...