nknapp16 Posted May 17, 2019 Share Posted May 17, 2019 90 Manche just passed inspection , but Oil pressure when starting is at 14 psi, then drops, even while revving. Any ideas? Engine sounds good, no bad noises, yet. Hoping its just a bad oil sending unit. Link to comment Share on other sites More sharing options...
MJXJjeepguy Posted May 17, 2019 Share Posted May 17, 2019 22 minutes ago, nknapp16 said: 90 Manche just passed inspection , but Oil pressure when starting is at 14 psi, then drops, even while revving. Any ideas? Engine sounds good, no bad noises, yet. Hoping its just a bad oil sending unit. Try that first if no help then it oil pump, very common in 4.0. Link to comment Share on other sites More sharing options...
cruiser54 Posted May 17, 2019 Share Posted May 17, 2019 Test the oil pressure with a gauge. You can rent one from a parts store. Link to comment Share on other sites More sharing options...
nknapp16 Posted May 17, 2019 Author Share Posted May 17, 2019 Sorry didnt mean sending unit, meant pump. 14 psi is w gauge when starting up, then slowly psi goes down to 10 psi. Did nothing when revving the engine. Link to comment Share on other sites More sharing options...
Eagle Posted May 17, 2019 Share Posted May 17, 2019 What make filter? Please don't say FRAM. Link to comment Share on other sites More sharing options...
nknapp16 Posted May 18, 2019 Author Share Posted May 18, 2019 Something worse, some no name, never seen before. Prior owner installed Link to comment Share on other sites More sharing options...
Minuit Posted May 18, 2019 Share Posted May 18, 2019 The oil pump creates flow, not pressure. The pressure comes from the bearing clearances in your engine, but the pressure still won't be up to snuff if the oil pump is worn out. The best oil pump in the world still won't lead to decent pressure if you can fly a B-17 between the main bearings and the crankshaft. Replacing or rebuilding the pump probably will help a little, but it's a toss up as to whether your engine is even capable of making good oil pressure anymore. Case in point my '89: Engine sounds like $#!& and has probably never been treated well. The engine abruptly lost oil pressure, leading me to rebuild the pump. On the original pump gearset, it made 60 psi cold, dropping very quickly to almost nothing when hot. The pump rebuild made no difference to the cold oil pressure, but it brought the warm idle pressure up to roughly 20 psi, which is just within spec for the 4.0L engine. Still not great (and it still drops like a rock as the oil warms up), but better. The oil pump was worn enough to reduce its ability to pump oil, but the bearings on this engine are just too worn to provide very good oil pressure once warm. When I did the RMS in my '91 I replaced the oil pump with a new unit. That made literally no difference to the oil pressure, warm or cold. That engine's in good shape and has been treated well its whole life. The lowest oil pressure I've ever seen from this engine is 30 psi at hot idle. The original oil pump was providing sufficient flow, and the bearings are tight enough to provide oil pressure well within the design specifications for the engine. Get a real oil filter and see if that improves things. My rule of thumb is Wix or Bosch, Motorcraft if it's a Ford. Link to comment Share on other sites More sharing options...
JMO413 Posted May 18, 2019 Share Posted May 18, 2019 Oil change with a good filter can't hurt anything. Who knows how old the oil is. Link to comment Share on other sites More sharing options...
knever3 Posted May 19, 2019 Share Posted May 19, 2019 With gauge? Do you mean the gauge in yhe cluster or a real one? The gage in the cluster always reads low compared to a real gauge.Sent from my SM-G920P using Tapatalk Link to comment Share on other sites More sharing options...
nknapp16 Posted June 13, 2019 Author Share Posted June 13, 2019 Gonna bring this thread back, I have been driving the Manche around more now that I fixed most of the steering problems. Installed new Crown Auto HD Tie Rod, Draglink, Track bar, all with new ends. After that I found that driver side ball joint is shot, so it still wanders a little. Anyways after the truck has been running/driving for awhile the oil pressure has been going down to about 10/11 psi at idle. Should I be nervous? As soon as you accelerate it goes back to above 20 psi, up to above 40 psi. Engine has a very slow oil drip, but nothing major. Thoughts? Link to comment Share on other sites More sharing options...
Eagle Posted June 13, 2019 Share Posted June 13, 2019 The factory spec for a NEW engine is 13 psi at idle and 37 to 75 psi above 1600 RPM. Just about every new 4.0L engine I've seen ran at 50 to 55 psi (hot) at 55 to 60 MPH. If you're getting 11 psi at idle and 40 psi at highway speed on a 29 year old engine, I think you're okay. Have you installed a decent oil filter yet? What weight oil are you running? For an older engine, I would run 10W40 or even 15W50 if you can find it. Link to comment Share on other sites More sharing options...
nknapp16 Posted June 13, 2019 Author Share Posted June 13, 2019 I have a WIX oil filter installed I'm sure it is 10w30 oil, I will try 10W40 next oil change. That's basically how I felt, just wanted to get some other peoples insight. Appreciate the responses. Link to comment Share on other sites More sharing options...
WesD Posted June 13, 2019 Share Posted June 13, 2019 General rule 10psi per 1000 rpm. You're OK. Link to comment Share on other sites More sharing options...
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