B5100E Low Oil Pressure at Idle

achtuning1 · Feb 2, 2016

Hi Everyone,
I recently purchased a B5100E back in the fall of last year for some clean-up work around the house. The tractor runs great and is as strong as a Kubota but after it has the chance to warm-up, the oil pressure light comes on at an idle. As soon as I raise the engine speed, the light immediately turns off. There are no noises of concern at this point in time, and there are no obvious oil leaks.

After performing a little research online, it looks like it might be a bad sending unit. The tractor is 38+ years old so it might be time to replace this switch. Furthermore, I do not have an oil pressure gauge so I am going to replace the sending unit to see what happens first.

I have heard of scenarios where the cam plug falls out but I really do not want to dismantle the tractor unless I have to.

From my understanding, these engines don't have hydraulic lifters or anything that need higher pressure at idle (as long as it raises whenever the rpm's rise).

If for some reason the new switch does not fix the issue, is it worthwhile cracking the engine apart or should i leave it alone and just continue to monitor the light?

Additional information: No Hour Meter (hours unknown)
Year: 1978
Tach: No
New Battery

Kubota Made Oil Filter: YES
Kubota Oil: 15W-40

The tractor is well-kept and serviced regularly. let me know if I forgot any information that might be of any value.

D2Cat · Feb 2, 2016

Kyle, welcome to the forum.

Do a search here for "cam shaft plug" or something similar. You'll find several threads detailing the situation.

The plug falling out would be my first guess. It was problematic in the early 5100,6100 and other tractors. Plug was aluminum, and after many heat/cool cycles of the engine the temperature differential cause the plug to be ejected.

Not really a big project. And I would not keep running my tractor knowing it had low oil pressure even at startup.

I used a tapered roller bearing to weld in the camshaft to seal one on a B6100. That was many moons ago!! If I remember, it took a few hours.

The important thing to remember is if you weld on your engine have a good ground and have it as close as possible to the part being welded!!!!! You don't want any power arcing through your bearings.

If you choose, you can get a sending uint here. http://www.colemanequip.com/Kubota_...tm_term=kubota parts&utm_content=Kubota Parts

Probably $16 range.

achtuning1 · Feb 2, 2016

Thanks for the feedback!

I think I will pick up a gauge on my way home tonight and test the pressure later this evening. I will report my findings once I have an update.

By chance, what pressure readings should I expect to see? Also, what size fitting should I buy?

1/8" BPST?

Thanks!

Kyle

North Idaho Wolfman · Feb 2, 2016

Yes it's 1/8" BSPT.

Note for others reading:
BSPT stands for British Standard Pipe Taper, common for Kubota's to use that pipe thread style.
Usual pipe threads are normally NPT, National Pipe Threads.

achtuning1 · Feb 3, 2016

Ok...

So last night I checked the oil pressure with a gauge I borrowed from a friend. When the tractor was warming, up I was getting approximately 16PSI. After letting it warm up, the pressure dropped to 6PSI at idle and 15 PSI at approximately 3000 RPM (i have no tach).

Since the sensors are set up to trigger the light at 6PSI, I decided to increase the idle speed the slightest bit to bring it out of 6PSI zone (to shut off the annoying red light

). I personally felt that the tractor idle speed was too low since day 1. Now at idle I get 10-11PSI and at 3,000RPM 16PSI.

Unfortunately, I must have cracked the old sensor while reinstalling it because the light is on constantly. I am going to pick up a gauge to install so that I can monitor the pressure more closely whenever I am using it. The tractor only gets ran 5 hours or less per year so I may wait to replace the cam plug.

I am going to pick up a new gauge at my local pep boys tonight while I wait on the 1/8 BPST to NPT adapter. A two inch gauge should fit in the existing opening where the stock kubota gauge would sit correct? I have a blank where the tach would sit on the dash.

Thanks for your help everyone. I am open to any feedback or questions.

Also, in case anyone was wondering, i used a 12 point 15/16 wrench to remove the old sensor.

Thanks,

North Idaho Wolfman · Feb 3, 2016

Deleted bad info

100 td · Feb 3, 2016

achtuning1 said:
The tractor runs great and is as strong as a Kubota
There are no noises of concern at this point in time
The tractor is 38+ years old
The tractor only gets ran 5 hours or less per year
Kubota Made Oil Filter: YES
Kubota Oil: 15W-40

The following info is mainly relevant if you have already found that your camshaft plug is in situ and not leaking.
If it were mine - my thoughts only
It's an old worn out tractor, is it worth spending money on rebuilding it for 5 hours use per year, I doubt it, only you can decide.
It's likely that all the bearings in it are worn excessively and are bypassing oil, as well as the oil pump itself, however it would be worth trying a couple of things IMHO.

While it's probably unlikely that the oil pressure relief valve is relieving, it may actually be relieving due to a weak spring or an out of round ball bearing or a worn seat, or there may be a tiny bit of crap under it that was pushed in there a long time ago.
I would remove the relief valve and clean and inspect it, I would replace the ball if it at all looked like it was not perfectly round, inspect the seat for wear, and replace if any wear, and add a couple of small brass washers behind the relief spring, as the spring will have lost tension over time.

If this DOES produce an increase in oil pressure, then order a new relief valve $25, or spring etc

If no result, next I would change the oil(leave the filter) to 25/60 or similar and see what pressure you get when hot and cold. Ideally ~25 psi minimum when running would be better.
If nothing changes when either of the above are done then I would decide whether it was worth spending money on, or just driving it until it stops. Your call!

D2Cat · Feb 3, 2016

I, NIW, led D2cat down a bad post path.

Diydave · Feb 3, 2016

I never worked on your model tractor, but back when I was mechanic on the turf farm, they had a L-185, with similar symptoms. What it turned out to be was cracked, hard O-rings, in the oil pump suction line(s). Not sure if yours has a similar setup, but it may be worth a look, in the parts book, to ID the O-rings, and see what it takes to get at them...

North Idaho Wolfman · Feb 3, 2016

Deleted bad info!

D2Cat · Feb 3, 2016

I, NIW, led D2cat down a bad post path.

North Idaho Wolfman · Feb 3, 2016

Deleted bad info!

Hondarancher4435 · Feb 3, 2016

North Idaho Wolfman said:
Deleted bad info!

I can't agree with that as I had a 7100 I forget the year but either way I had identical issues to this poster. Pulled the front end and the cam plug was gone. Was able to get a new plug at dealer once installed oil pressure more than doubled. It's only a few hours of work and you shouldn't leave it like that with low oil pressure you will ruin a good engine in short order even if you only use it 5hrs a year.

100 td · Feb 3, 2016

Page 21 of the parts manual for a B5100E shows a "Plug, Blind" which appears to be in the end of the camshaft, is that it?
15261-96860 PLUG BLIND or later model 15261-96880
http://kubotabooks.com/AutoIndex/index.php?dir=Tractor Parts Manuals/&file=B5100E.pdf

North Idaho Wolfman · Feb 3, 2016

Deepest apologies to all... Had a DUHHH moment and was thinking of the freeze plug on the front of the motor.

The B5100,6100,and B7100 has a bolted cover where the others have a freeze plug.

Thanks to D2cat for calling me and setting me strait.
I think it was the 1/4" of snow that sent me off on a spin!

And yes Hondarancher4435 And 100td you are both right.

achtuning1,
As others have said, I would jump on it and fix it now and not later, it is a fairly easy fix.

100 td · Feb 3, 2016

North Idaho Wolfman said:
Deepest apologies to all... Had a DUHHH moment and was thinking of the freeze plug on the front of the motor.

And yes Hondarancher4435 And 100td you are both right.

Well NIW, we all make mistakes every now and then, I take my hat off to you for acknowledging said mistake. I also take my hat off to you for all the great information you have provided to members of this forum. (And I'll have plenty more questions to ask in the future!)

The information I have posted is now most likely unnecessary as I was working on the supposition that there was no plug, so I will address and edit this. Hopefully achtuning1 will now pull the covers and replace the plug and have many more seasons of use from his machine.

85Hokie · Feb 4, 2016

Maybe someone can clear this up for me .....I own a 92 B7100 HST......

when did Kubota realize they had a problem with the cam plug ?(other than day one)

If they "fixed" it ....when was the fix installed?

I really do not want to rip the face off the happy girl just to find out that the plug is still......plugged!!!!

I have searched high and low - watched a few youtubes too - but everything I read says something to the effect - "kubota knew about it and then fixed it"

I am just curious if/when any of this is true - cause we all know that everything that is on the internet that is printed is the truth, the whole truth, and nothing but the truth!!

thanks for any input on this ....leaky subject!

D2Cat · Feb 4, 2016

NIW I have to say "ditto" to what 100 td says in his last post. You disseminate information on so many machines, how do you store it and find it and post it so fast?

Thanks for all your help!

The information you post here is like skipping a rock on a pond, the ripples just keep on going. Probably the only thing you see is the original poster, but what about those who come behind, do a search, and bingo...they find their answer and go on...never to be heard from again. Or to stop in and say thanks!!

I first "met" you when working on my L305. Trying to get a seal replaced in the front hub. You coached me right through it. Thanks again.

Daren Todd · Feb 4, 2016

85Hokie said:
Maybe someone can clear this up for me .....I own a 92 B7100 HST......

when did Kubota realize they had a problem with the cam plug ?(other than day one)

If they "fixed" it ....when was the fix installed?

I really do not want to rip the face off the happy girl just to find out that the plug is still......plugged!!!!

I have searched high and low - watched a few youtubes too - but everything I read says something to the effect - "kubota knew about it and then fixed it"

I am just curious if/when any of this is true - cause we all know that everything that is on the internet that is printed is the truth, the whole truth, and nothing but the truth!!

thanks for any input on this ....leaky subject!

If your oil pressure light isn't coming on at an idle, then I wouldn't worry about going in there. As the old saying goes, if it ain't broke, then don't fix it

I would do a quick look on the side of the engine and make sure your sending unit isn't disconnected. Or did you hook up an oil gauge to the old girl? Can't remember

85Hokie · Feb 4, 2016

Daren,

"If your oil pressure light isn't coming on at an idle, then I wouldn't worry about going in there. As the old saying goes, if it ain't broke, then don't fix it I would do a quick look on the side of the engine and make sure your sending unit isn't disconnected. Or did you hook up an oil gauge to the old girl? Can't remember"

light is only on - when it aint running!!!

I might place a gauge on the sending unit this spring - I looked last night, the unit still has a wire hooked to it and working!

thanks again!

B5100E Low Oil Pressure at Idle

New member

Well-known member

New member

Moderator

New member

Moderator

Active member

Well-known member

New member

Moderator

Well-known member

Moderator

New member

Active member

Moderator

Active member

Moderator

Well-known member

Well-known member

Moderator