Hydraulic fluid dipstick question

[WV NATIVE]

I’ve got an odd question about the hydraulic fluid dipstick on my B7500.

When I pull the dipstick on my hydraulic fluid it is barely touching the stick but when I insert it again and pull it back out it shows full.

Anyone else have that issue?

It’s the only piece of equipment I own that’s acts like that. I thought the vent may be clogged up but it breathes free.

Not sure which reading I should believe.

Pictures aren’t the best representation but you get the idea. First pull of the stick looks dry - second doesn’t.

 

[leonard65]

Ok same exact thing on my B2320 I never posted it because I didnt want anyone to think I was crazy.Also so hard to read, clear fluid on the orange stick.

 

[WV NATIVE]

Ok same exact thing on my B2320 I never posted it because I didnt want anyone to think I was crazy.Also so hard to read, clear fluid on the orange stick.

If you’re crazy then I guess I am too.

 

[North Idaho Wolfman]

Put a piece of black shrink wrap on the dipstick or dye in the fluid, to read it better.

 

[Runs With Scissors]

I vote for “dye”.

Cheap, easy and effective.

 

[WV NATIVE]

I can see the fluid - the stick is dry the first time I pull it.

I can’t understand why it’s on the full mark after it’s reinserted.

 

[BAP]

As far as the oil being on the dipstick, believe the second reading. I think that because the dipstick has a tight fit at the top, it traps air and doesn’t allow the oil to come up the tube to proper height when the dipstick is in place. When you pull it out, the oil then can fill the tube up properly. Metal dipsticks like in the engine, don’t have that really tight fight at the top so the air can move out of the tube and allow the oil to maintain the proper height.

 

[imarobot]

As far as the oil being on the dipstick, believe the second reading. I think that because the dipstick has a tight fit at the top, it traps air and doesn’t allow the oil to come up the tube to proper height when the dipstick is in place. When you pull it out, the oil then can fill the tube up properly. Metal dipsticks like in the engine, don’t have that really tight fight at the top so the air can move out of the tube and allow the oil to maintain the proper height.

Be interesting to pull the dipstick out just enough to let air in and wait a bit before pulling it out all the way to see if the oil level on the dipstick went up.
I would try this myself, but I don't have one of those machines.

 

[D2Cat]

If at any time the dip stick shows a higher reading then other times go by the highest reading. No matter the physics involved, the fluid is in a container (transmission) and the actual volume doesn't change in any circumstance you describe.

 

[imarobot]

If at any time the dip stick shows a higher reading then other times go by the highest reading. No matter the physics involved, the fluid is in a container (transmission) and the actual volume doesn't change in any circumstance you describe.

Very true, but I'd still like to see the physics of why this happens

 

[nbryan]

The o-ring seals near the top of the dipstick prevent the transmission fluid from filling the dipstick tube from below.

The o-rings seals stop the trapped air under them to escape and allow the oil below to rise up and level with the rest of the tranny oil in the case.

Just pull the dipstick and re-check after a few seconds. It's always been like this for my B2650.

 

[Bee-Positive]

Put your finger on one end of a straw.
Put the open end of the straw in a glass of water.
Note how far the water goes up into the straw.
Take your finger off the end of the straw.
Note how far the water goes up into the straw.

 

[Shawn T. W]

Hey! At least you don't gotta wipe the dipstick off first, just pull it out, confirm it's clean and dry, re-insert and check again ...

On my Kawasaki in my JD, you unscrew the cap that is the end of the dipstick, pull it off, wipe it dry, reinsert ... BUT DO NOT SCREW IN, just rest on top of the threads, then pull out and check level!

I use dye in my hard to read sight glass ...



That's TWO DROPS per gallon of fluid, I got a LIFETIME supply! (Wear gloves!)

https://www.zoro.com/kingscote-dye-tracer-liquid-liquid-red-4-oz-506250-r4/i/G5130815/?origin=sayt_typeahead

 

[JonM]

never knew this was a thing ive always pulled the stick wiped it then put it back in to get the reading.

 

[hagrid]

Put your finger on one end of a straw.
Put the open end of the straw in a glass of water.
Note how far the water goes up into the straw.
Take your finger off the end of the straw.
Note how far the water goes up into the straw.

Now my milkshake is contaminated with JD TransGard.

 

[GeoHorn]

I’ve got an odd question about the hydraulic fluid dipstick on my B7500.

When I pull the dipstick on my hydraulic fluid it is barely touching the stick but when I insert it again and pull it back out it shows full.

Anyone else have that issue?

It’s the only piece of equipment I own that’s acts like that. I thought the vent may be clogged up but it breathes free.

Not sure which reading I should believe.

Pictures aren’t the best representation but you get the idea. First pull of the stick looks dry - second doesn’t.

View attachment 175754 View attachment 175755

It’s not unique to your Kubota. It is also common on Yamaha outboards. It’s due to a trapped air-bubble that escapes when the dipstick is first pulled. The correct reading is obtained after it is re-inserted and then pulled.

 

[Hugo Habicht]

I can see the fluid - the stick is dry the first time I pull it.

I can’t understand why it’s on the full mark after it’s reinserted.

The only explanation I have is that despite the vent there is a small vacuum/pressure somewhere preventing the oil to flow back into the reservoir. By pulling the dip stick you remove that and the oil level goes to the correct value.

I remember vaguely that other people mentioned this phenomenon here.

 

[GeoHorn]

It’s not hard to understand…when you consider the change-in-design of dipsticks. In earlier designs it was simply a metal blade with a small metal-cup dust-cover…. Nothing air-tight about it.
(In fact, it was a major source/ingress of dust when open crankcase vents were dispensed-with and as the crankcase was evacuated by intake-manifold vacuum.)

The “modern” versions are actually sealed, air-tight with rubber or nitrile ‘plugs” ….that prevent any trace of venting at that point…..(presumably to keep out dust…but also to seal the crankcase for emissions containment. It makes for more effective PCV operations, etc.)

Many newer vehicles have gotten rid of the dipstick entirely to facilitate that system.

 

[William1]

My method for a dip stick is always a double pull. I pull, wipe, insert, pull, check level.

 

[Runs With Scissors]

Although it's not entirely germane to the conversation, it's similar.

There are some vehicles where you have to pull the filter BEFORE you drain the oil. If you don't, it creates a vacuum and not all of the oil will drain out.

Our Caravan has such a motor,........................ and "yes" , I found out the "hard way" ......

So I can see where there might be situations (as @GeoHorn and @Hugo Habicht have pointed out) where the drain/refill systems create, or rely on, a vacuum of some sort.