Guys, changed the oil in my 5.0L (130000kms) and used GTX3 (Castrol, I think), when I first started it there was a slight knocking which I assumed to be normal while oil pressure built up (I did fill the filter before fitting however)...I have never heard it on a cold start up though, but anyway, the knocking disappeared and I thought all was good...had done maybe 50k's on the new oil and was sitting idling for around 5 mins and the oil pressure gauge light comes on and i get the beep beep from the dash...I shut the car down thinking I've lost oil or the wire on the sender unit is loose...all checked out ok...so I started the car again...and the oil pressure was around 12-15 psi at an idle...which i think is way to low...I've decided to change the oil but didn't know whether to change the grade or brand...anyone else had trouble with the GTX3 ?? I don't want to go away from the recommended grade of 15w40, maybe it needs 15w50, but I'm beginning to think GTX3 must be crappy oil...I had heard a few stories about it but had dismissed them as myths...any help would be really appreciated...thanks

So you checked the oil pressure with a mechanical gauge?

15 psi is way low. Mine gets down to 40 when the oil has thinned out and am sitting at idle... thats with a mech gauge...

I'd do another oil change and prob new filter as well (just in case its blocked... and they only 7 bucks). Try some penrite in your chosen viscosity... i dont think gtx3 is the greatest oil... fairly cheap isnt it?

try magnatec - i've had no probs with that!

If it does it again with the thicker oil check your oil pressure sender

I have this same problem on magnetec and the other comparable oils. not often and only after she's warm! scares me!

if you drive an au falcon or fairlane
there could be a voltage drop across the oil gauge
to check this prob start the engine and connect a jump wire from the alternator bracket to battery earth check and se if the oil gauge rises
if it does make up a heavy earth wire from the alternator bracket to battery earth
oh and do this at engine operating temp

when the guage wire open-circuits(ie cometh offeth) then the guage maxes out..

Mine sender played up latre last year, would be fine for 10-15 mins then drop off the scale. I changed Oil, Filter and it persisted. Changed sender and all is good. Bout 85 from Fraud, and you must use genuine, as there is no aftermarket option. Also can be a b**ch to get out without the correct sized deep socket.
Brett

the ford oil sender and cluster arrangement is a joke , 90% of the ones i have been in are all over the place all the time , i fail to take any notice of them anymore, if it knocks or taps thats another thing but if it does not dont worry about it. many dealers will even say we cant fix it (mainly due to the time and parts involved) then the customer having a fit at the bill. not cheap at 80$ an hour.