Tractor Repair: High Oil Pressure with Kubota L2500, high crankcase pressure, vent tube

Question
QUESTION: I have a 1998 Kubota L2500 tractor that has been maintained well and has been problem free, until now. It recently, on several occasions, has blown the "oil fill" cap off, indicating high crankcase pressure. I have checked the crankcase vent tube and it is clear and venting very slightly. I am not sure how much is normal.

I drained the oil and looked at the filter and both looked normal, will change with new and see what happens. I use Kubota 30w oil and Kubota filters. Any other suggestions would be appreciated.

ANSWER: How many hour are on this tractor?
This is ususally an idication of clogged breather tube or excess blow by
Since you have checked the vent I would check the compression.
Let me know what you find out and we can go from there.

---------- FOLLOW-UP ----------

QUESTION: Thanks for the quick response,490 hrs on counter. Seems like very little but really only use it during the summer to mow. I didn't know exactly how much air would come out of vent tube, so I stuck the end of it into a bottle of water and saw some bubbling but not a lot. Not too experienced on diesels and how to check compression. I assume you are thinking a "ring blow by". There is significant oil at base of exhaust pipe. Actually seems to be running normal. The cap really blows off violently after about 20 minutes, even at idle.

Answer
Your right about this being low hours to think new rings but I have seen a Kubota m105 with 5oo hours needing a complete rebuild with scored clynder and piston.
As far as bubbles coming from the vent tube you will always have some. As the piston goes down in the clyinder it has to force some air out that was BELOW the piston.
to check compression you may have to find someone to do this as a diesel compression test kit is needed. you will use either the glow plug fitting or the injector inlet, depending on the kit used.
The compression should be about 300-400 psi with no more than 25% difference between clyinders. Diesels require extremely high compression as this is what ingnites the air/fuel mixture.
If you pull the dipstick out a little while it is running what does it do?
Let me know your findings.
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