Cat D4D, 83J2406, hydraulic tank is holding pressure. Is this correct? Service manual doesn’t mention anything about it and parts book doesn’t show the cap missing any parts. The cap has a drilled hole for vent that goes around the threads but is still outside the gasket seal on the filler neck so it won’t vent the tank. No other vents on tank. Can’t believe the tank should have pressure on it. Am I wrong? Anybody seen this?
How much pressure are you talking? I have a 931B loader and it is designed to have some pressure in the tank. I think it's only 2 or 3 PSI. When you remove the hyd. cap you can hear the air being bled off. I loosen the cap a bit and let the pressure bleed off before fully removing. It's not like it would shoot the cap across the room though. The pressure keeps the hyd. pump from cavitating. I think the pressure can also be used to detect leaks in the system. If I see the oil level is a little low, from weeping cylinders, etc., and come back the next day to add oil and the tank still has pressure indicates to me there is not a major leak in the system.
Some tanks are pressurized so pumps don’t cavitate
Thanks. Not much pressure. Just a hiss for a few seconds when you crack it open. Guess the vent hole I see is just to make sure it vents when you crack it. Just don’t remember it being this way but not like It is opened all the time.
The hydraulic tank is part of the Hydraulic Control Group, not the tractor. It would need the S/N from the plate on the tank to find an illustration of it. As BLS pointed out, many hydraulic tanks are designed to pressurize slightly when the air above the oil heats up, especially if the system uses a vane-type pump. This assists in preventing pump cavitation. Even when the oil is cold you can still get a bit of hiss from the cap as you unscrew it. The only doubt is whether or not your tank is equipped with a relief valve that is supposed to prevent the pressure getting too high. Either post the S/N of the Hyd Ctrl or a photo showing the top of the tank if you want to take this issue further.
Right, S/N of tank is 62G15720. Few pictures. Thanks!
Our D4D hydraulic tank was always under pressure after the machine was used.
What does the fill cap look like?
You have a 141 Hydraulic Control. There is no relief valve on that tank. The cap design provides a form of safety valve (ball & plate) to allow the pressure inside the tank to relieve as you (slowly) unscrew the cap. In fact the following words are probably cast into the top of the cap if it is original - "Remove Slowly. Screw down tight." Try unscrewing the cap when the machine has been left overnight. I'd wager you'll still get a bit of a hiss from it.
So in a nutshell some pressure in the tank and/or when you remove the cap is normal.
It was on ours.
Well, that covers it, no worries then. Thanks everyone.
Where's all the leaking oil and accumulated dirt the hyd tank is supposed to have....or is that just mine?
Was that way awhile ago but got cleaned and we repainted the whole machine when we rebuilt the engine. Was the second paint job since we’ve owned it. First was 25 years ago when we got it and did a lot of work back then. Just need a new under carriage and it will be really nice. Looking after market or good used.
So now that you teased us with a picture of the super clean oil tank, whats the rest of it look like?
I expect a white lab coat to be in the photo.