I've just put a new engine into my EF Fairmont (as the previous owner overheated it and seized it). I've put Castrol Magnatec 10w40 oil in it which I now think is not the correct oil...

When I first got it going it had good oil pressure (about 5 on the gauge when driving) but now 8weeks later it has dropped to about 2 when driving and the low oil pressure light comes on and a buzzer beeps sometimes when at idle....

Do you think I need to just change to a thick oil? 20W50?

Thanks

when you say new.. do you mean new re built or a "new" second hand runner???

Sorry: New as in a 2nd hand runner.

unless the sender is faulty, usually low oil pressure when warm is usually bearing clearences or oil pump wear..
how many kms were on the replacement engine??
it wont hurt to go to a 20w/50 if the engine has a few kms on it..

The new engine has done 200,000km. It has low oil pressure hot and cold. There is a hose which goes into the top of the engine via a small plastic nozzle, this pipe isn't currently on as it has split and just falls off... Would this be causing the car to loose oil pressure?

If you know the hose I'm talking about where would I get one? Ive tried automotive parts stores like Repco etc but they don't have anything like that...

Thanks

that would be the pcv/ crankcase breater hose, wont have any effect on oil pressure.
you should be able to get one from a ford spare parts dealer..

the oil pressure, i can only suggest trying another pressure sender,
do you have the one from your old engine??