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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

81 f150 sudden oil pressure loss and valve noise

 
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Old 06-15-2019, 07:54 PM
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81 f150 sudden oil pressure loss and valve noise


hello. so the other day I bought an 81 f150 long box supercab 4x4 351m c6 to use as a runaround beater truck on property. it ran a drove fairly well for 3 days, then yesterday I drove it to my dad's place, shut it off, then 30 minutes later on restart it had very low oil pressure and a valve was clacking pretty loud. I checked the oil level and it was within spec but I topped it up anyway. I tried it again today as it's much cooler and I thought the thicker oil might help. it was a bit better for minute but dropped again after a few minutes and the valve never did quiet down.

a full rebuild is not in the cards but if like to get it usable again. where would you recommend I start? and what would cause it to go from fine on shutoff to broken on restart a few minutes later?
thanks
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Old 06-15-2019, 08:51 PM
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A sticky hydraulic lifter.
 
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Old 06-16-2019, 06:55 AM
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After you bought it did you just change the oil? If so, the detergents in the new oil could have broken loose some sludge and it has clogged up the pickup to the oil pump.
 
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Old 06-16-2019, 10:57 AM
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Originally Posted by Franklin2 View Post
After you bought it did you just change the oil? If so, the detergents in the new oil could have broken loose some sludge and it has clogged up the pickup to the oil pump.
I actually didn't change the oil. it was pretty clean when I got it. the valve covers leak pretty good so I assume it gets topped up quite frequently.

wouldn't a sticky lifter be the result of low oil pressure rather than the cause?

would pulling the pan be the best next step? I've read that it can be quite a hassle
 
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Old 06-16-2019, 11:29 AM
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what weight oil are you adding?
I always change the fluids when I get a new to me vehicle, doesn't matter what they look like.
I look at it as a starting baseline.
 
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Old 06-16-2019, 12:57 PM
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Pulling the oil pan would be a logical next step, though like you mentioned a big one. You could pull a valve cover and see what it looks like inside. If it's all sludged up you can know this engine was probably not taken care of and will most likely need changing out or a full rebuild. You really haven't run it long enough and lived with it long enough to know how much oil it uses. But it would be a waste of time to commit to surgery on a engine that is pretty much wore out.
 
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Old 06-16-2019, 02:07 PM
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Originally Posted by dustyroad View Post
what weight oil are you adding?
I always change the fluids when I get a new to me vehicle, doesn't matter what they look like.
I look at it as a starting baseline.
usually just 10w30. I also tossed in a bottle of stp to see if it would quiet the valves at all. it worked on the 2.9 in my bronco 2 so I figured I'd give it a try. I didn't notice anything but I'm also trying not to run it much until I get it sorted
 
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Old 06-16-2019, 02:25 PM
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Originally Posted by mrq View Post
usually just 10w30. I also tossed in a bottle of stp to see if it would quiet the valves at all. it worked on the 2.9 in my bronco 2 so I figured I'd give it a try. I didn't notice anything but I'm also trying not to run it much until I get it sorted
I'd change the oil to a X-40w and new filter but that's just me. See if the pressure comes up any and if it helps with the noise.
Previous owner may never have ran a good zinc oil in it and like franklin2 said, could be quite sludged up.
 
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Old 06-16-2019, 02:41 PM
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Originally Posted by Franklin2 View Post
Pulling the oil pan would be a logical next step, though like you mentioned a big one. You could pull a valve cover and see what it looks like inside. If it's all sludged up you can know this engine was probably not taken care of and will most likely need changing out or a full rebuild. You really haven't run it long enough and lived with it long enough to know how much oil it uses. But it would be a waste of time to commit to surgery on a engine that is pretty much wore out.
Dave I think you have the order wrong I would pull the valve covers to give a look see. As said it could be sludged up or a bent push rod, rocker that is no good and let the push rod fall out.
Once the covers are off and things look ok you can run it to make sure all the rockers are moving as they should. If they leak now a little more oil spraying wont hurt.
Dave -----
 
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Old 06-16-2019, 05:44 PM
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Most all the old Fords that I have had did have some valve train ticking or clacking. I think he is worried about the oil pressure problem, which can be causing the noisy valve train. You are correct, I would pull the valve cover first and see what the engine looks like inside.

One of the joys of buying a used vehicle. You never know what you are getting sometimes.
 
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Old 06-16-2019, 10:27 PM
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Originally Posted by Franklin2 View Post
Most all the old Fords that I have had did have some valve train ticking or clacking. I think he is worried about the oil pressure problem, which can be causing the noisy valve train. You are correct, I would pull the valve cover first and see what the engine looks like inside.

One of the joys of buying a used vehicle. You never know what you are getting sometimes.
a few of mine have noisy valve trains and my big bronco has low oil pressure at idle and a bit of a tick but it was gradual. I just think it's strange to go from no noise and okay oil pressure at shut off and 0 pressure and loud clatter on restart. I can see if I was revving it hard or cruising for a long period but I literally idled up the drive. I'll pull the covers sometime and see if there is a glowing green arrow pointing at something obvious. I wasn't expecting much for 600 bucks but I'm still bummed
 
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Old 06-17-2019, 07:45 AM
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I had an older Dodge pickup with a 318 years ago. The motor had a lot of miles, the valve seals were so bad, that pieces of them ended up in my oil pan, and the oil pump sucked them up and broke the oil pump shaft twice before I parked it. I've never torn apart a Ford 351, but if the oil pump runs off the distributor as did the Dodge 318, I'd say pull your distributor and check the shaft. The noise you're hearing may not even be a lifter. There are other reasons they could break, just plain fatigue maybe. Usually if this happens, you will have a total loss of pressure, and that doesn't sound like your problem, but I thought I'd throw it out there, easy to check it. Okay, so I just read the last bit of your thread right before this reply, and you mentioned it did have a total oil pressure loss? Well, I would say it's oil pump shaft. NJot sure what that looks like in Ford V8 considering the dizzy is in the front, but I'm sure you guys know that already. The only Ford motor I've worked on is my 300 I6, so I'm not much help there.
 
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Old 06-17-2019, 05:02 PM
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well I pulled the drivers side cover off and found that both pushrods on the second to back cylinder dropped into the valley. I'm not much of a mechanic but I'm betting that's part of my problem. may also help explain the slight miss and low power it's had since I got it. I'll try to fish them out and see how mangled they are. I can't see the lifters right now but I have a handy little borascope adapter for my phone so I might be able to peak in the valley and check their condition. would this also have caused low oil pressure?
 
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Old 06-17-2019, 08:04 PM
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Originally Posted by mrq View Post
well I pulled the drivers side cover off and found that both pushrods on the second to back cylinder dropped into the valley. I'm not much of a mechanic but I'm betting that's part of my problem. may also help explain the slight miss and low power it's had since I got it. I'll try to fish them out and see how mangled they are. I can't see the lifters right now but I have a handy little borascope adapter for my phone so I might be able to peak in the valley and check their condition. would this also have caused low oil pressure?
Yes it would. The oiling system is set up to have resistance thru out.
With 2 push rods missing you have removed some of that resistance.
Also the lifters could have popped out of their home and cause a BIG oil leak.

Use the scope to see if the lifters are still in the bores and maybe check if the others are still in place.
You might get lucky and just replace the push rods and be good to go.
Dave ----
 
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Old 06-19-2019, 01:03 AM
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Originally Posted by mrq View Post
well I pulled the drivers side cover off and found that both pushrods on the second to back cylinder dropped into the valley.
Can you see the pushrods? Or are they possibly missing? Years ago, I knew of a guy pulling a dirty trick trying to sell a car with a rod knock. He removed the two pushrods and it quieted right down. This was a Chevy V8, or should I say V7.

No idea if the same dirty trick would work on a Ford engine.
 

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