Kubota engine oil

[MHarryE]

I agree with Hunter29, Kubotas oil viscosity spec is out of date, or just flat out wrong. My Kubota manual says it is okay to use 15w-40 below 32F. What if it is -10F, so that is still okay? Not for me. 5w-40 is a superior viscosity for most applications we use these engines and tractors in. I have 2 Kubotas and 1 older Ford, and they all get 5w-40. In fact, all of our vehicles get 5w-40, it is my 'fleet' oil. I have attached an engine oil viscosity verses temperature chart from an old Caterpillar manual I copied a few years back. I have read many oil viscosity recommendation charts in my career, and this one just makes good sense, for any engine. Philip.

Remember this is a Caterpillar engine oil recommendation. Oil viscosity requirement depends on the bearing to journal clearance. Wider clearance, higher viscosity oil. Auto engine shift to 5W-20 and 0W-20 oil came with improved machining capability allowing them to reduce bearing clearance. My M7 workshop manual gives the factory specification crankshaft journal to crankshaft bearing clearance as 0.0012 to 0.0029 inches. An engine built to the tighter clearance could have cold start issues at 0.0012 clearance with heavier oil. I use 5W-40 synthetic in mine. My Cat mini-excavator has a very loose engine and gets 15W-40.

 

[PHILIP8N]

Remember this is a Caterpillar engine oil recommendation. Oil viscosity requirement depends on the bearing to journal clearance. Wider clearance, higher viscosity oil. Auto engine shift to 5W-20 and 0W-20 oil came with improved machining capability allowing them to reduce bearing clearance. My M7 workshop manual gives the factory specification crankshaft journal to crankshaft bearing clearance as 0.0012 to 0.0029 inches. An engine built to the tighter clearance could have cold start issues at 0.0012 clearance with heavier oil. I use 5W-40 synthetic in mine. My Cat mini-excavator has a very loose engine and gets 15W-40.

What I am trying to show is what a really good viscosity chart looks like, and this Cat chart does just that. I am confident using that chart for all high speed diesel engines, clearances and loads are similar between manufacturers. My point is that Kubota's chart in my manual is archaic, and flat out wrong. The Kubota manual still list the use of single weight 10W, 20, and 30 weight oils! And as I stated earlier, the Kubota manual approved use of 15w-40 at temperatures below 32F, inclusive of -10F! That is wrong and poorly written. Philip.

 

[RjCorazza]

What I am trying to show is what a really good viscosity chart looks like, and this Cat chart does just that. I am confident using that chart for all high speed diesel engines, clearances and loads are similar between manufacturers. My point is that Kubota's chart in my manual is archaic, and flat out wrong. The Kubota manual still list the use of single weight 10W, 20, and 30 weight oils! And as I stated earlier, the Kubota manual approved use of 15w-40 at temperatures below 32F, inclusive of -10F! That is wrong and poorly written. Philip.

Kubota has a long history of poorly written lubricant and coolant requirements. I did like the CAT PDF, which was well written.

 

[MHarryE]

Okay, having helped create the Cat SEBU referenced, it’s intended for Caterpillar equipment. Cat, selling equipment everywhere in the world, has to contend with availability of lubricants everywhere, including extensive sales to the US military who has a set of lubricants they stock and dictates you will use these or you won’t do business with us. I fought some of the specs that went into that SEBU for my equipment and with my crew discussed saying compartment lubed for life rather than change factory fill to the lube available in many parts of the world.

Having said that, the Cat SEBU would be more appropriate for Kubota engines than what Kubota publishes. After all the Cat C3.8 is the very popular Kubota 3.8. And the Cat SEBU does cover Cat by saying to use an oil with the low end viscosity required for your temperature. That was the important point I was trying to stress. In my climate where winter temps are often below 0°F, 15W-40 will not fill the small gap on the loose side where the oil input hole is located. I’ve seen cold start test bearings comparing 5W-40 synthetic (no wear) and 15W-40 mineral oil (extreme wear) and know I don’t want 15W-40 in my 3 important Kubotas. The RTV and GR2120 get 15W-40 like my Cat mini-excavator and the Cummins engine in my Case combine.

 

[Bullwinkle123]

My Kubota MX 5400 (purchased in 2020) operator manual & dealer say to use 15W-40, and so that's what I use. Just a data point.

 

[LouNY]

15-40 was a good multi grade oil for diesels years ago.
Anyone using it now in cold weather is asking for troubles,
if that engine is out in cold weather she may start fine but if you put a mechanical pressure gauge on it,
then start it up cold and watch how long it takes to get a good pressure reading,
then repeat after it has been run and worked enough to have the oil heated up.

Then switch to a 5W-40 and do the same you will quit using 15-40 in the cold weather.
The almost instant oil pressure reading compared to a few seconds.
None of my engines run 15-40 in the winter.
Heck not even in the summer, T6 synthetic 5W-40 year round.

 

[MHarryE]

15-40 was a good multi grade oil for diesels years ago.
Anyone using it now in cold weather is asking for troubles,
if that engine is out in cold weather she may start fine but if you put a mechanical pressure gauge on it,
then start it up cold and watch how long it takes to get a good pressure reading,
then repeat after it has been run and worked enough to have the oil heated up.

Then switch to a 5W-40 and do the same you will quit using 15-40 in the cold weather.
The almost instant oil pressure reading compared to a few seconds.
None of my engines run 15-40 in the winter.
Heck not even in the summer, T6 synthetic 5W-40 year round.

You got it! So many of the old axioms don’t hold water. My first project at the new company Cat bought in 1989 was putting a Cat 4 in a machine using its highest power rating - 107 HP. Tier 4 that same engine (not really same as virtually every part changed) was cranking out up to 225 HP with much higher reliability. So many things changed but the mounting holes were in the same location so it would bolt in. Lines and accessories changed but that’s how much more power things like CRI, turbo design, etc., brought on. And lubes were part of that.