Hey Folks,
First time poster here,
I was recently given an old tractor (not a Kubota, but with a Kubota Z500 engine), that had been sitting for approximately 17 years and managed to get it running fairly easily. I don't know what the previous owner had done to it nor do I know why it had been sitting for that long.
(Also I'm not a native english speaker so please excuse my broken english)
Backstory:
After the first 20-30 minutes of just driving around the idiot light got mad at me, so I turned the engine off, checked the oil level (which was fine), fired it back up and the light turned off.
I drove it home, hooked it up a test gauge and noticed that sometimes the pressure would drop for no apparent reason. Changed oil and filter but still had the same issue.
Decided to drop the oil pan and found that the bolt that was supposed to hold the center main bearing assembly in place was just missing??? (as seen in the picture below)
(FYI: The oil pickup screen was installed, I just removed it to replace the O-ring)
I ordered a new bolt, washer and gasket, installed them and reassembled everything.
Before starting the engine I checked the oil pressure while cranking with the decompression lever pulled and got about 1.8-2bar (~26-29psi).
At cold idle it had 2-2.4bar (~29-35psi)
At cold ~75% WOT it had 2.5-3bar (~36-44psi)
At warm idle it had 1.5-2bar (~22-29psi)
At warm ~75% WOT it had 2.2-2.7bar (~32-39psi)
Pressure never dropped below the point where the oil light should turn on (according to the gauge).
Now, even though these aren't great results, all this seems acceptable to me and meets the requirements stated in the manual, however at (cold engine) slow idle the oil light flickers very dimly and gets a little brighter as the engine warms up (but light never full on). If I bring the throttle up to a high idle the light stays off.
Replaced the sending unit and still the same problem.
Tested with an air compressor the (new) Kubota sensor shuts the light off at ~ 0.8bar (~12psi), even though the minimum idle oil pressure spec is 10psi.
I've also noticed that the needle on the test gauge was fluctuating (at the pace of the engine) quite a bit ~0.6/0.7bar (~10psi) which seems exessive to me. (I am using a tested and calibrated gauge)
Image illustrating the needle fluctuate at cold idle
Probably also worth mentioning is that when I let off the accelerator, the needle fluctuates around 1bar (~15psi) until the engine has throttled down enough.
Now, I know that the Z500 engine has a rotor type oil pump which may cause slight fluctuation in oil pressure but it feels like 10+ psi would be way too much.
I've heard of the cam plug falling out on some engines but I don't believe that to be my issue as from what I've read the pressure would be a lot lower.
I've also read another post where someone with the same engine was experiencing simmilar issues and he "fixed" it by replacing the Kubota pressure sender with a general automotive sender that was set to go off at the same pressure as the Kubota one.
Is the Kubota sensor too sensitive/inaccurate?
The engine itself is running smoothly, no knock, idles fine, sounds fine, fires right up (after glowplugs for 15 sec), has very little blowby (no smoke, just a bit of air) out of the breather tube.
Oil is 15w-40 (API CF-4 rated)
So here are my question's:
Is it normal for these engines to have that much fluctuation in oil pressure (considering its over 40 years old now)? And am I fine running it as is or do I need to worry about it?
Is the light flickering dimly (at low idle) the result of the fluctuating oil pressure? Overly sensitive switch maybe? If so, should I use a different switch?
Or has my engine got bigger Problems?
With kind regards,
DG06
First time poster here,
I was recently given an old tractor (not a Kubota, but with a Kubota Z500 engine), that had been sitting for approximately 17 years and managed to get it running fairly easily. I don't know what the previous owner had done to it nor do I know why it had been sitting for that long.
(Also I'm not a native english speaker so please excuse my broken english)
Backstory:
After the first 20-30 minutes of just driving around the idiot light got mad at me, so I turned the engine off, checked the oil level (which was fine), fired it back up and the light turned off.
I drove it home, hooked it up a test gauge and noticed that sometimes the pressure would drop for no apparent reason. Changed oil and filter but still had the same issue.
Decided to drop the oil pan and found that the bolt that was supposed to hold the center main bearing assembly in place was just missing??? (as seen in the picture below)
(FYI: The oil pickup screen was installed, I just removed it to replace the O-ring)
I ordered a new bolt, washer and gasket, installed them and reassembled everything.
Before starting the engine I checked the oil pressure while cranking with the decompression lever pulled and got about 1.8-2bar (~26-29psi).
At cold idle it had 2-2.4bar (~29-35psi)
At cold ~75% WOT it had 2.5-3bar (~36-44psi)
At warm idle it had 1.5-2bar (~22-29psi)
At warm ~75% WOT it had 2.2-2.7bar (~32-39psi)
Pressure never dropped below the point where the oil light should turn on (according to the gauge).
Now, even though these aren't great results, all this seems acceptable to me and meets the requirements stated in the manual, however at (cold engine) slow idle the oil light flickers very dimly and gets a little brighter as the engine warms up (but light never full on). If I bring the throttle up to a high idle the light stays off.
Replaced the sending unit and still the same problem.
Tested with an air compressor the (new) Kubota sensor shuts the light off at ~ 0.8bar (~12psi), even though the minimum idle oil pressure spec is 10psi.
I've also noticed that the needle on the test gauge was fluctuating (at the pace of the engine) quite a bit ~0.6/0.7bar (~10psi) which seems exessive to me. (I am using a tested and calibrated gauge)
Image illustrating the needle fluctuate at cold idle
Probably also worth mentioning is that when I let off the accelerator, the needle fluctuates around 1bar (~15psi) until the engine has throttled down enough.
Now, I know that the Z500 engine has a rotor type oil pump which may cause slight fluctuation in oil pressure but it feels like 10+ psi would be way too much.
I've heard of the cam plug falling out on some engines but I don't believe that to be my issue as from what I've read the pressure would be a lot lower.
I've also read another post where someone with the same engine was experiencing simmilar issues and he "fixed" it by replacing the Kubota pressure sender with a general automotive sender that was set to go off at the same pressure as the Kubota one.
Is the Kubota sensor too sensitive/inaccurate?
The engine itself is running smoothly, no knock, idles fine, sounds fine, fires right up (after glowplugs for 15 sec), has very little blowby (no smoke, just a bit of air) out of the breather tube.
Oil is 15w-40 (API CF-4 rated)
So here are my question's:
Is it normal for these engines to have that much fluctuation in oil pressure (considering its over 40 years old now)? And am I fine running it as is or do I need to worry about it?
Is the light flickering dimly (at low idle) the result of the fluctuating oil pressure? Overly sensitive switch maybe? If so, should I use a different switch?
Or has my engine got bigger Problems?
With kind regards,
DG06
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