Tankmaster sight gauge level going down without pulling out the valve.

[Rollerball]

My oil tank has an Atkinson Tankmaster sight gauge assembly, like this:

https://www.fueldump.co.uk/products/Atkinson-Tankmaster-Valve-%2b-Sight-Gauge.html

Normally it's necessary to pull the 'pull to read' plunger to get a current oil reading on the sight gauge (the green bead will then drop down a little), however recently I've noticed that the level on the gauge (green bead) is going down (at the normal rate!) even though I've not pulled the 'pull to read' plunger, therefore it's acting as if the pull to read plunger has already been pulled out, even though it's pushed in.

I should emphasise that there is no oil leak whatever, the oil in the tank is going down as normal in accordance with how much I use the boiler. There's no oil or smell of it around the sight gauge assembly, or anywhere else for that matter.

I guess that a seal on the pull to read valve is perhaps not sealing correctly?

Along the same lines, I've also recently noticed that when I do pull the pull to read plunger there is some oil on the stem (in other words the part of the stem that is only exposed when the valve is pulled out). I've not noticed that until recently. Again, I'll stress that the oil is only on the stem.

The valve is also pretty stiff, not just to pull out but to push back in. It was last replaced about five years ago I think.

I see that it's possible to buy just a new pull to read valve:

https://www.fueldump.co.uk/products/Tankmaster-Pull-to-Read-Valve.html

Perhaps if I just replaced that it would resolve both of the aforementioned issues (oil level and oil on the valve stem)?

Looks like I just need to turn off the oil at the main wheel valve, unscrew the old pull to read valve and install the new one, is that correct?


Also, if I was to leave things as they are is there any danger of an oil leak developing bearing in mind the issues above? Or is that valve, etc all self contained and the 'worse case scenario' is that the gauge level drops automatically?

 

[oilhead]

There is probably some detritus that has fallen down the tube and part blocked the orifice between the valve and the tube. First off, I would turn off the oil at the wheel, remove the sight tube and clean it out, clean the valve body at the tube connection, pull out the 'read' plug and clean again, pushing it back again.
Once this is done, open the main valve, and see if you have a leak, If you do, turn off the main valve again and remove the 'pull' valve by unscrewing it. Clean off the 'o' ring and inspect it for cracks. Reassemble and check again. If you still have a leak, you may be able to replace just the 'o' rings, or buy another 'pull' valve.

 

[Rollerball]

Thanks very much. When you say a 'leak' I guess you mean a leak of oil going into the sight gauge tube when the plunger hasn't even been pulled to read?

Is this a 'problem' as such or likely to be a problem in the future? I mean no oil is leaking outside of the assembly, etc. Just curious really - I won't be leaving it of course, if I decide I'd rather not attempt the procedure I'll call in my usual oil certified plumber.

Also, how about the aforementioned oil on the stem of the pull to read plunger that's only visible when the plunger is pulled out, is this likely related to the currently 'self adjusting' level in the sight gauge tube? I should say that I forgot to mention that the oil on the stem often has some streaks of brown, I initially thought this could be some copper grease that I vaguely recall once applying to the pull to read valve - it quite possibly is that, I'm guessing it's not rust as how would metalwork soaked in oil begin to rust?

EDIT: Incidentally, if I go ahead and replace the pull to read valve myself, is it worth putting some PTFE tape on the thread just to be on the safe side?

 

[Rollerball]

Update: have now replaced the pull to read valve, other than the old valve being tough to pull out (once unscrewed) all went well.

Regarding the old valve, if you look at the part here:

https://www.fueldump.co.uk/products/Tankmaster-Pull-to-Read-Valve.html

see the area on the stem with the spring - on the old valve the spring has a coating of surface rust as does the stem but only on the section of the stem that the spring covers - might this imply that there is some ongoing rust inside the large metal body of the Tankmaster assembly where the pull to read valve screws in? I'm now wondering if the whole assembly needs to be replaced.

 

[oilhead]

I think you will find the main body is aluminium, so any rust is going to come from the only steel parts, the spring and the shaft. There is always a chance that some water may get in there from the orifice in the assembly retaining nut. Nothing to worry about.

 

[Rollerball]

I see, hadn't thought of that! Thanks for the advice.

I was surprised how tough it was to pull out the old valve once it was unscrewed, are they normally tricky to extract or was that likely to have been caused by the surface coating of rust?

 

[oilhead]

The 'o' rings are a tight fit and if they have perished a little and swollen, they become even tighter.

 

[Rollerball]

Thanks, that makes sense.