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post #17 of (permalink) Old 14-03-2017, 14:44
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Join Date: Jul 2012
Location: Hunstanton
Car: MGF
Posts: 3,338
ok.. being Mr Dangerous again, i shoehorned the pressure gauge into my MGF Freestyle jiggle pipe return in the header tank line.

started the engine, checked for leaks... gauge didnt move at first the pressure takes time to build up.. but as soon as i revved the engine, the pressure started to climb.

1. the temp gauge climbing to normal.. idle revs,

2 the pressure gauge reading at that time.

it climbed to that point quite fast.. and was very rev dependent.. it didnt drop below, but at every idle point it settled a little higher up.. and over idle revs.. say up to 2000 rpm i could see 8psi


revving higher to 4000 rpm i could see the gauge reading 13 plus psi.. near the 1 bar limit.. i couldnt take a pic of that and rev at the same time.. but it shows that the system pressure is pump force dependent.. as the pump turns faster, the pressure goes up .

at each time i let go of the revs and it idled, the gauge stabilised at about 7psi..

at idle.. engine warm.. no fans on..

at that point i had seen enough for this shoehorn example... i know now that the pump can push 13 plus psi into the system.. at normal operating conditions...

when i turned the engine off, the pressure dropped from 7 to 5 psi.. and stabilised.. sitting like that as the engine cooled... very gradually falling slowly.

i will post more... when i have some better hose connections and fittings..

i am pleased to see the gauge working... its a very useful bit of kit... i shall explore it further now i know it works.

of particular interest to me.. is now i understand what the normal operating idle pressure should be in a good sound system with no leaks... is a pressure switch to change a led from red to green... i.e. if there is a leak or low pressure below say 5 psi at idle something is wrong... the system cant get up to pressure... likewise it would also tell me of high pressure.. ( from a cylinder leak into the system.. )

much more useful than a coolant level switch.. since the system will change pressure before the fluid leaks low, and one would see abnormal pressure quicker... long before the vent cap vents at 1 bar.. just under 15psi. ie.. if 7 psi at idle is about normal, then 12 psi at idle isnt

it took 50 minutes today as posted this reply for the gauge to reach 2 psi... from stopping the engine..

Last edited by Incony; 14-03-2017 at 15:12.
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