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MG MGA - Bleeding oil pressure guage

I have an oil leak and need to replace the flexible hose leading to the oil pressure guage. It's now on order.
I was wondering whether bleeding the line at the guage is necessary. I would have thought that whenever the engine is turned off, the oil is going to slip back down the tube anyway and be replaced by air. If so, no point in bleeding it!
On researching on the net, some seem to say the air doesn't need to be bleed as it will still give a very similar reading on the guage as oil would.
Just wondering if anyone has any views?
Thanks, Graham
g Victors


I have certainly never bled mine in 45 years, and it always works OK. As far as I can see it doesn't actually matter as any air that is there will transmit the pressure.

Paul Dean

"I was wondering whether bleeding the line at the guage is necessary."
The pressure gauge works just as well on air pressure as on oil pressure so there is no need to bleed the line or the gauge. Cheers - Dave
D W DuBois

There is some advantage to bleeding it. As originally equipped, the connector block between the flex hose and steel pipe has a small restrictor orifice to damp out fluctuations of the gauge needle due to pulsing from the oil pump. If the pipe is full of air the gauge response will be slow, possibly taking several extra seconds to show the pressure reading, especially on start up. If you bleed the air out leaving only liquid oil in the line all the way to the back of the gauge, the gauge response will be quicker.

Once bled and sealed, there is no way for air to get into the tube. It will always be filled with oil even after prolonged storage.

The seal face between the pipe and gauge is a flat mating surface. There was originally a small leather washer to seal this joint. I did at one time buy the small leather washer from Moss Motors, but I have never installed it, and the joint stays sealed without the packing piece (on my car). If yours may leak, then it needs the leather washer seal.

Barney Gaylord

Thanks for the advice.. Much appreciated.
g Victors

This thread was discussed between 13/04/2015 and 14/04/2015

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