Id be more worried if the oil has the correct api classification. diesel oils are not the same as oil for gas engines. This would likely cause far more damage than a light weight oil. I know automotive oems changed oil ratings from 10W30 to 5W30 and then 5W20 without making changes to the engines. This was done for fuel economy. Like others mentioned this will probably cause some additional wear but I would guess it would be minimal especially if its synthetic.
If your oil does not have one of these ratings drain it no questions asked.
API Service Classification CI-4, API Service Classification CH-4, or ACEA Specification E3.
Per john deere
Choose oil viscosity based on the expected air temperature range during the period between oil changes.
John Deere PLUS-50™ oil is recommended. John Deere TORQ-GARD SUPREME™ and oils meeting ACEA Specification E4/E5 may also be used.
Other oils may be used if they meet one or more of the following:
API Service
Classification CI-4, API Service Classification CH-4, or ACEA Specification E3.
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Xring100,,, Thank you for posting this information.. I had typed up the same type of reply last night, hit the wrong key and lost the post.. I was glad to see this info in your post.. It's true about the thinned out oil for fuel economy..
(CAFE),, corporate average fuel economy is a federal program imposing increasing fuel efficiency ratings.. None of the manufacturers can easily meet these guidelines, and it's costing a lot of money to try..
The first, fastest, and cheapest way for them to get closer to the requirements was across the board lighter oil weight recommendations... It has nothing to do with a new fangled engine, no such thing...
Some of the oils recommended now in the states, aren't for sale in any other countries,, yet the engines are the same...
I don't know if the original poster is ever coming back, but I recommend putting some real oil in the tractor and his truck too !
Lastly,, Machine Lubrication published a report a couple of months ago that reported fudging on stated weights. The report indicates that a large amount of tested oil is coming out thinner by actual weight than the posted weight on the can... I believe the report as it fits in with the other underlying changes mentioned above...
Now,, I don't follow the government,,, could care less about politics,, but I know one thing,, if the government gets involved in anything, it's going to be a mess,,, and they are a mile deep into engine oil at this time...
We are running 10w40 in our new cars,,, 15w40 in our diesels,,, 30 weight racing oil in our antiques..