I have a 90 f150 5.8 with a terrible oil leak ill lose a qt every 30 mins or so but only when driving or revving but not at idle it is only on the passenger side mainly off the cat cover a little off the transmission and oil pan bolts its all over underneath though that's just where it drips I just replaced the passenger side valve cover gasket I just noticed the drivers side valve cover was lose and clearly had oil puddle on it by the bolts I tightened it but still leaking the same amount I'm replacing the gasket later today. My question is can my oil pressure sending unit be the culprit it does go wacky at idle some times (if its not the valve cover) its on the opposite side but with pressure it could spray out and work its as around the engine I think? I'm pretty sure its not the oil pan gasket because it seems to be coming from above that and it doesn't leak all the time same with the rear main its dry inside the inspection cover and with how much I'm losing it should be covered if not puddles of oil in there. What could be causing this the drivers side valve cover? The oil pressure sending unit? Some other sensor on the back of the motor?

 

Sending unit could definitely be the problem. Shortly after I got my 95 5.0L I was driving and looked in the mirror to see tons of smoke. Lot of oil coming out and leaving a trail on the road. Long story short, the oil pressure sending unit went out. New one fixed the problem.

 

I just don't understand how it would get to the passenger side to where that's the only side that drips

 

So it still leaks the same amount after I replaced the other valve cover I'm going to try and do the oil pressure sender today what size socket is it I think I read somewhere its a "1 1\16 6 point socket and could my intake manifold have a bad rear gasket causing the leak??

 

If the intake was leaking I feel like the truck would barely run, and probably have an issue with the coolant as well.

Start with oil related gaskets, replace the oil pressure sending unit, go from there.

 

It runs great aside from needing plugs and wires I've never done a intake gasket on these motors but I've done plenty of intake gaskets on FE motors 352 360 390 and I know its a 4 piece gasket the two for the heads and one in front and one in the rear and if that's not seated right it will still run fine but leak oil out of the front/rear gaskets could this same thing happen on a 351? Or is it if one part of the gasket isn't good the whole thing is bad?

 

yes, these windsor v8's can and do develop oil leaks from the intake manifold gasket.
i would clean the engine off really good and then try to see where the leak is coming from.

 

Buy a couple of cans of Gunk .....spray it down with it........take a garden hose and hose it off.............Then fire it up and rev it up......may need a helper to hold the throttle while you crawl around .....keeping your eyes open............That is the quickest way to find an oil leak......Don't just keep throwing parts at it hoping it will fix it........

 

You can also buy some fluorescent dye that goes into the oil. You would need a black light to see the glow of the dye though. It makes finding leaks much easier although I only usually use it for small leaks.