Engine oil capacity of JD790?

[RoyJackson]

So I maybe I have what appears to be too much oil and maybe I don't. But snce the engine is a blueprinted mechanical manufactured item it would appear the correct amount of oil is as stated and correct. For whatever reason, the dipstick is reading wrong?
Any thoughts on this?

I don't think you're reading it wrong. It most assuredly looks overfilled.

This is what I'm going to suggest:
Drain the oil out completely (let it set with the drain plug and filter off for at least 15-30 minutes). Handle the oil filter carefully since it's new and can be reused...I wouldn't reuse the oil...oil is cheap.
After that 15-30 minutes, re-install the oil filter. Then add 3 qts of oil...let set for 5 minutes or so, and check the level. Then add another 1/2 qt, recheck the level. If it's showing on the stick, start the engine long enough to flow the oil (a minute or two), shut the engine down and let it set 5 minutes...then recheck the dipstick. I'm going to guess the oil level will be low to half way up the stick. If so, I'd leave it there...or maybe add just a bit more (no more then 1/2 qt!).
Keep track of how much oil you are using...
Also, I can't recall if the oil filter is horizontal or vertical...I can't recall filling it before installation though.

I cannot recall the volume between the low and high marks of the dipstick...but I'm pretty sure it's not a full quart.

 

[Henri88]

It would seems that it holds closer to 4 quarts than 4,3 as mention in the manual, although the manual says ''approximately''. I would trust the dip stick before the manual. I personally would remove the oil filter and drain it and put it back on and see where that would bring me. As Roy mention, which ever way you decide to do this, I would not reused the oil.

 

[sixdogs]

I'll do what Roy suggested but I have to wait until March when it warms up and i can get the tractor out of the barn again. Stuff gets packed in a little tight and unless we get a warm spell, it's sleeping for a few months. Still, I can't see how there can be that much variation in capacity. I'm going to order a correct dipstick just in case the one I have came from something else. You never know.
I'll report back.

 

[sixdogs]

I couldn't wait until March and a sunny 55 degree day had me out in the barn today and I think I figured it out and learned something in the process. Roy got me thinking last night when he warned of overfilling oil so I looked into it and got out my owner's manual. In big print, as we have all seen is "DO NOT OVERFILL".
The problem, it seems, is that an overfilled crankcase can cause the crankshaft to drag in the oil and foam it enough to starve the main bearings for oil.
I took the 790 oil filter off--cold--and drained a very small of oil out. Just a small amount caused the overage in the dipstick to drop by nearly half of the overage. In other words, the excess was nowhere near as bad as feared and I suspect the configuration of the oil pan caused the oil to gain quickly on the dipstick once the full line was reached. Maybe, because overfilling is so bad for the engine, the maker made it this way to scare owners into not overfilling. Anyway, two dumps of a very small amount --1 1/2 to 2? ounces-of oil brought the oil back to the "full" mark. It now has probably 4.25 qts of oil in it and is correct.

Now, I have two other tractors I accidentally overfilled when filling from a 5 gallon bucket and the same thing happened. On my Kubota L4300 that holds 8 qts, it looked like I was a quart over based on the distance the line would be if I was a qt low. Just three dumps of very little cold oil from the filter got the dipstick back to the full line. The oil must be full exactly at the bottom of the crank and it must not take much additional oil to gain on the dipstick.
Same thing with 9 qts in my Deere 5520. It looked like I was a quart over and two dumps of that filter brougt the oil back to the fiull line. This filter held more oil but is was only a few ounces.
Anyway, that's my story and what I learned. At 63 years of age I thought --err...knew-- I had learned it all but that's what I discovered. All this seems perfectly logical in retrospect and maybe everyone knows but me but I do know I will never overfill my oil.

 

[Henri88]

Glad to hear it work out ok. I use that oil filter trick a few time and it work great, that's why I suggest it to you. Trying to remove just a small amount from the drain plug can be challenging and messy. :thumbsup:

 

[RoyJackson]

I'm glad you didn't wait until Spring (your original intention).
I'm guessing you drained about a 1/3rd to 1/2 a quart.

Good lesson to all, BTW...never fill the sump completely at first...leave it 1/2 to one quart down...top off if necessary.

 

[sixdogs]

I'm glad you didn't wait until Spring (your original intention).
I'm guessing you drained about a 1/3rd to 1/2 a quart.

Good lesson to all, BTW...never fill the sump completely at first...leave it 1/2 to one quart down...top off if necessary.

No-no-no, Roy. Just a couple to three ounces and that's max. Sure surprised me. I figure the crank fills up most of the space in the pan and just a little oil
raises the oil level on the dipstick a much greater amount than the pan space below the crank. The way I figure it has to be is that the max oil level is exactly at the bottom of the crankshaft and the reason overfilling oil is so dangerous is that it submerges the bottom of the crank. Which cause the oil to foam since the crank beats it and can starve the main bearings of oil.

This leads me to my earlier thoughtthat the reason my friend's Deere (Yanmar) engine main bearings went bad was maybe not because the oil level too low from neglect but maybe it was too high from an overfill of good intention? Maybe Yanmars are especially suceptable to overfilling? Anyway, Roy, thanks for alerting us to the dangers of an ooverfill oil situation and how dangerous it can be. Wow have I learned something.