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Car Forum / Ford / Ford Cars / August 2008'88 F-150 oiling problem
A friend's 1988 Ford F-150 4WD with 351 EFI engine would have normal oil pressure upon starting cold, but the pressure would go down to zero when the engine warmed up. He replaced the oil pump and the problem remained. Someone advised him that these engines were known to do this if there was slight warpage on the pump mounting face, which would increase as block temp increased, causing it to lose prime or suck air. Is anyone else familiar with this problem and if so, what is the recommended remedy. Engine has about 125K miles. > He replaced the oil pump and the problem remained. FIRST, did you screw in a mechanical oil gauge to check the oil pressure? I bet not. If you do not have access to one or can't afford a mechanical oil gauge, put in a new oil sender and tell us what happens. Tthanks for your reply. That's a fair question about the mechanical gauge, it would have been my first suggestion as well. He is just going by the dashboard gauge, which shows good oil pressure when the engine is cool, and goes down to pretty much nothing when it gets up to operating temperature. And when warmed up, the lifters start clattering loudly -- it's VERY obvious that there is no oil pressure by the sound of the engine -- to the point that there's no need to even question the gauge. No way would you even think of driving it making that sound. Grasping at straws he's tried running a can of motor flush through it, inserted a grabber tool into the drain hole on the off chance a rag could have gotten left in the pan, etc. He's a pretty adept mechanic but has suffered a stroke and is unable to do stuff like he did in the past. The information he was given about these engines being prone to the above mention oil pump glitch seems plausible. Was wondering if anyone else has had a similar experience. Thanks again. > Tthanks for your reply. > That's a fair question about the mechanical gauge, it would have been [quoted text clipped - 15 lines] > Was wondering if anyone else has had a similar experience. > Thanks again. Not likely the pump would suck air. The pumps pressure side is all that attaches to the block along with the drive shaft. The most likely problem is the oil sender. For many years now, Ford has used a guage that has the capability to operate as a real guage but, does not. It is setup with a sender that makes it work more like a light so that any acceptable pressure will register in the middle range of the guage. It only leaves the middle when the pressure drops too low. Unfortunately, the senders are less reliable than the old senders and frequently fail. It is likely the truck did not require a new oil pump. I suggest the sender be replaced. If that does not correct what the guage displays, a mechanical guage test is in order. Most of the small block Fords will run around 60 psi hot at cruise. It may drop down around 25-30 when idling. It should be OK if it drops to the 10-15 PSI hot idling and topping out at 35-40 if it is not being driven or worked hard. I am also wondering if he replaced the pump without completely removing the pan in which case he may not have gotten the pickup out for inspection. If not, the pickup screen may be clogged. I don't think I have ever seen a plugged screen cleaned by flushing the engine. IT is also possible the pressure regulator plunder in the pump is stuck open. Only a mechanical guage will be any help on this one if the sender doesn't fix it. Lugnut if the pressure is really droppng to nothing it would be clattering . ive seen worn out cam bearing cause this on this engine. if your useing 10w30 a heavier oil like 20w50 or a straight 30w might help it ,but fixing the cause would be better. ive rebuilt engines since 1973 and cant remembr a warping pump surface problem on the 351 , or any other ford for that matter.there was the ocasional core plug that popped out of the block oil gally under the intake manifold that would destroy oil pressure. lucas ---------------------------------------------------------------- http://www.minibite.com/america/malone.htm |
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