B6100E Oil Light on after working on a hot day

CosmicKubota

New member
Hello,

I am now the third owner of the family Kubota B6100E with about 1400 hrs on the clock. It was purchased new in the early 80's, and was used primarily for mowing with a 3pt finishing mower.

I just took ownership of the tractor this summer to mow a 5 acre lot. I noticed after mowing for an hour or so that when I brought the engine rpm back down to idle, that the oil light would come on. If I raised the RPMs to about half, the light would go out. I changed the oil with a Shell grade for Diesel engines along with fresh oil and air filters. I also drained the coolant and refilled with distilled water and a touch of anti freeze. I also cleaned the outside of the radiator and made sure the fins where clean and free of dirt.

None of this seemed to make a difference. The oil light goes out after a cold start at idle, but after working the tractor, the oil light now may flash on even at full throttle on a hot 90deg day. My brother whom I purchased the tractor from said it's been doing this for awhile. He even thought it was something normal, but he's an electrical engineer, not a mechanic.

What's going on with this tractor? Is there a problem with the oil psi or is the problem with the radiator and engine cooling system? I ask this since shutting the engine down for few minutes to cool seems to help with keeping the oil light off at idle until after the engine is worked for a few minutes.

I plan on attaching a mechanical oil pressure gauge to see for sure where the problem lies. If the problem is with the main bearings, oil pump or connecting rods, then is it possible to rebuild and repair? The engine sounds solid. I don't hear any abnormal rod knock.

Thanks in advance for any feedback offered.
 

California

Super Moderator
Staff member
Site Supporter
I went through the same thing with my Yanmar of similar age. All it was, was the oil pressure sender had worn out after 30 years.

You could buy the inexpensive Harbor Freight test gauge like I did to diagnose what is going on. But I suggest just take your present sender into Autozone or NAPA and match it to one off a 70's Datsun/Toyota/Subaru. That's all there is to it. About $7 for the whole project.

And tell us how this turns out!
 

CosmicKubota

New member
Good News.

I finally got around to "attempting" an install of a mechanical oil psi gauge today on my B6100E. Unfortunately the brass fitting included with the kit wasn't the correct size, just a hair too large. Thankfully I had ordered a new oil pressure switch and had it handy, so I went ahead and installed it. It was clear the old sender unit was bad because it was difficult to unscrew the sending wire due to the screw spinning within the sender unit.

I worked the tractor hard mowing some tall grass for about 1.5 hrs on a 80 plus deg day.

No blinking light. Not even at idle. Only when I kill the engine does the light turn on, as it should.

I'm a happy camper now knowing my baby is running as it should and will for many years to come.

I love these Kubota tractors.

Thanks for the input California. I plan on buying some brass fittings so I can still install the mechanical gauge along with the stock oil sending unit.
 
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