Dropping oil pressure
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Dropping oil pressure
1995 F150 4.9L at start up the oil pressure is a good 50psi, as soon as the coolant temp gets to half way on the gauge, the oil pressure starts to go down to 15psi in idle ( at a light). Not losing any oil or coolant, just curious as to any ideas why its dropping so low.
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From: Des Plaines, Illinois
I assume you're using a good mechanical gauge to check the pressure.
15psi hot at idle isn't incredible, but it's easily passable. A good rule of thumb is 10psi for every 1000rpm.
Cold startup and operation will always yield a higher oil pressure because the oil is thicker than it is at full temperature operation.
How many miles are on this engine? The six runs forever, but over time they will start to break down just like any other mechanical device. 15psi doesn't really scare me, and it wouldn't scare Ford either. After all, the dummy gauge on the dash doesn't trip until you go under 6psi.
15psi hot at idle isn't incredible, but it's easily passable. A good rule of thumb is 10psi for every 1000rpm.
Cold startup and operation will always yield a higher oil pressure because the oil is thicker than it is at full temperature operation.
How many miles are on this engine? The six runs forever, but over time they will start to break down just like any other mechanical device. 15psi doesn't really scare me, and it wouldn't scare Ford either. After all, the dummy gauge on the dash doesn't trip until you go under 6psi.
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I'm using a mechanical gauge. The truck has 216000km. Now I did dig out 4lbs of sludge from under the valve cover and have flushed the engine about 8 times (includung oil changes) in the last month. Got the truck running smooth with the one problem of decreasing oil pressure when it seems the t-stat opens. Others have suggested it may be a headgasket prob, but I'm not showing any signs of loss of oil/coolant, no smoke, nada. As long as its RPM is above 1000, it has great pressure.
Lead Driver
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From: Concord, NC
If the screen is clogged, the pressure loss would appear at higher oil flow rates, i.e. as rpm increases, not at idle. If the plugged screen allows 5 GPM and idle requires 4 GPM, the clogged screen will not have any affect on idle pressure. Plus, hotter, thinner oil would increase the flow rate capability of the clogged screen, which is opposite of what is happening here.
I don't think it would be a head gasket problem, as it usually wouldn't affect pressure unless there was a substantial amount of water in the oil, which you likely would have noticed by now. The low pressure could be due to increased clearances on the main and rod journal bearings, or it could be caused by a worn oil pump. If pressure comes back quickly with RPM, I would lean more towards a worn oil pump, but without checking either the bearing clearances or the pump, I wouldn't just blindly replace the pump. I think you should be fine idling at 15 psi, even though it is a little on the low side I think it is acceptable. What weight oil are you using?
I don't think it would be a head gasket problem, as it usually wouldn't affect pressure unless there was a substantial amount of water in the oil, which you likely would have noticed by now. The low pressure could be due to increased clearances on the main and rod journal bearings, or it could be caused by a worn oil pump. If pressure comes back quickly with RPM, I would lean more towards a worn oil pump, but without checking either the bearing clearances or the pump, I wouldn't just blindly replace the pump. I think you should be fine idling at 15 psi, even though it is a little on the low side I think it is acceptable. What weight oil are you using?
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Joined: Nov 2008
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From: McKenzie River
15 PSI at idle is not too bad, I have seen "healthy" 350 Chevy's drop to 8-10 on a hot day at idle in gear.........Do drop the pan and get the sludge out of it, when your there you can inspect the oil pump screen.
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Joined: Jul 2004
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From: Cottage Grove, WI
i agree 15psi at idle is not bad at all. if the psi jumps soon as you hit the throttle, your pickup should be fine also. but again, if you found a ton of goo under the valve cover, pulling the pan and cleaning it out wouldnt hurt either.
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thank you everyone for your input. I'll have to remove the oil pan and take a closer look at the screen. Only thing that'll stump me is getting the engine mount bolts removed so I can lift the engine high enough to pull the pan. Any how, thanks again for your help.
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