No oil pressure

[mil9657]

     Hi, I'm having a strange problem maybe you guys can help me out with. I have a 1972 f100 with a 360 in it, while driving home from work last week the oil pressure gage went to "L".  I did notice a lack of power when going up hills as this was happening but no other out of the ordinary things. The truck has always ran towards the low side even after I replaced the oil sending unit.  Once I got it home I parked it, didn't check the oil until the next day and it didn't show on the dip stick. I decided to drain what oil that was left ( 1 to 2 quarts ) put a new filter on and fill it back up.
     The truck started up and ran fine other than smoking a bit, it hadn't done that before. I drove it maybe 5 or 6 miles and the oil pressure was good, better than I had ever seen it.  So a day or so later I drove it about 12 miles at a constant 60 mph. Around about 10 miles I noticed the oil pressure gage started heading towards "L" and the just flat lined. The truck lost power but I was able to limp to a parking lot.
     I looked under the truck and noticed oil dripping from the bellhouseing. I checked the oil and it was not showing on the dip stick again. I let the truck sit for an hour and checked the oil again now oil was on the dip stick up to the full mark. Started it back up drove it back home and the same thing happened again lost oil pressure and power. I lipped it home to the garage and there it has remained.
     I took the valve covers off to check for any obvious signs of obstructions in the oil return passages but could find none. What do you think is going on with this thing?  Thanks

[cjshaker]

The fact that the oil level went from not showing on the dipstick to reading full indicates you have serious drain-back issues. If the engine is all original and stock, I'd guess you have busted pieces of valve stem seals blocking return passages somewhere. While they usually block the return passages at each end of the heads, they aren't always easily seen if they are down in the passage a ways. It could also be sludge build-up in the passage as it goes around the head bolt. It's a tight area that needs to be clear, and any obstruction will hinder oil return pretty drastically. Or it could be a combination of the 2...which is not exactly uncommon for an original engine with that amount of age on it, especially with the use of older oils and possible lack of regular oil changes at some point through its long history.

It also sounds like you have a leaking rear main seal on the crankshaft, which is likely where the oil from the bellhousing is coming from. At this point, I'd say a complete tear down is in order because you likely have some bearing and/or ring/cylinder/piston damage due to oil starvation. Probably not what you want to hear.

[machoneman]

2X on a complete teardown. 

[mil9657]

     I was afraid it would be something like that. Thanks for responding to my post

[My427stang]

Pull the valve covers, clean the returns and see how she does.

If you were happy last week, you'll be happy again     Sounds like it was filling the valve covers. 

[427mach1]

It also sounds like you have a leaking rear main seal on the crankshaft, which is likely where the oil from the bellhousing is coming from. At this point, I'd say a complete tear down is in order because you likely have some bearing and/or ring/cylinder/piston damage due to oil starvation. Probably not what you want to hear.

Another possibility is that since the valve covers are filling up, oil could be leaking out of the valve cover rail where the intake meets the head....  From there it can leak down the back of the block, bellhousing, etc.

[cammerfe]

To add to the other comments, it might be worthwhile to try blowing air under pressure down the drainbacks. If they're clogged by stem seal 'swarf', the air might clear them out. That's not necessarily a good result, for the stuff is then more likely to get stuck on the screen on the pick-up tube and cause obstruction there. But since it won't cost anything except the possibility of rocker cover gaskets, it might give some indication of what's going on.

KS

[Joe-JDC]

Take a good strong flashlight/LED light and shine it into each valve spring and look for a missing valve stem seal.  If you see one, take a shop vacuum and rig up a small tube to the vacuum hose and vacuum out the oil drain holes in each end of each head.  You will hear the part unplug if it isn't already in the pan.  If you have access to a bore scope, run it down each oil return hold in the ends of each head.  There are several options to try to find the reason why the oil level changed.  Joe-JDC

[Falcon67]

I'm with Joe - first thing I'd try is the shop vac and a kludge of reducers to get a 1/2" hose over the oil returns and see what comes up.  Valve covers seems like the only logical place for that much oil to hide for that length of time.  Old valve seals in engines dry out and shatter like glass. 

[cjshaker]

I don't disagree with continuing to run the engine if it's cleaned out and pressure returns, I see engines ran dry on oil all the time where I work, but when you lose power due to lack of oil pressure, that means things are getting tight. The engine is living on borrowed time at that point. I know it might seem ok at first, but it's a matter of "when", not "if". But if it's just a point A to B truck, I guess you've got nothing to lose if it starts knocking or is down on power.

Can you even tell when a 360 is down on power? 

[frnkeore]

Just as a note on how much you can get away with on "0" oil pressure, back in '95 I both a '78 LTD, for the 302 engine core. It was almost 30 miles from my place. The engine ran great but the oil light was on and there was valve clatter. I reved it and there was no knocking, what so ever so, since it was going to be just a core, I decided try to drive it home, keeping it under 40 mph. Got home w/o any knocking. I figured if it started knocking, I'd call a tow truck.

When I pulled it down, I found that the alum/nylon, timing sprocket had lost some nylon and that the hex drive was twisted off. There was a small gap in the oil screen and I found the nylon in the pump BUT, all the crank journals where fine and worn only .001, after polishing them. I used the crank, as is!!

Very hard to believe, I know but, it DID happen.

[WConley]

When I was at Ford, we sent a new employee to a meeting in Toledo, in a company pool car.  Apparently, at the start of the 70 mile return trip, the oil light came on, but "the engine sounded fine".  As soon as the Tempo (ugh!) got up on the lift in the X-Garage, the missing oil drain plug became apparent.

Our vehicle coordinator, Ralph, knew where this car was going at the end of its six-month stint in the pool.  Executives could buy the six month old pool cars at steep discounts.  This particular executive was a known ass.  Ralph could have easily had a new engine swapped in, but instead he had the mechanics install a new drain plug and top up the oil. 

We never heard a thing about it.  The car drove fine for the rest of its time in the pool.

[machoneman]

I advised a total tear-down for one reason: It's a lot cheaper to throw a mildly damaged engine back together (better if no machining is needed and one got really lucky!) than one that ends up with spun bearings, a badly damaged crank, maybe a rod through the block's sides. etc.

Hey, even finding FE parts is getting hard to do let alone all the time it would take to line up and get shipped the needed parts. Throw in machining and the rest and one maybe could have avoided a lot of pain.

And yes, I've also seen a few zero oil pressure engines come back to a long life with a minimal correction (just re-filling the near empty crankcase is a good idea!). Yet, more than that did end up locked-up with a severely damaged engine.
 

[Joe-JDC]

Bob and others, I was not disagreeing with your assessment about rebuilding, merely trying to help with determining what is the root cause of the loss of oil pressure, and oil.  If that can be determined and it is reasonable easy to fix, such as valve job and new seals, or dropping the pan and cleaning it and the screen, then a work truck can be kept in service.  A daily driver is a little different for most of us than a weekend warrior FE.  I personally would be pulling the heads and pan and checking bearings, and getting a valve job, as well as new timing set as a minimum.  Joe-JDC

[machoneman]

Bob and others, I was not disagreeing with your assessment about rebuilding, merely trying to help with determining what is the root cause of the loss of oil pressure, and oil.  If that can be determined and it is reasonable easy to fix, such as valve job and new seals, or dropping the pan and cleaning it and the screen, then a work truck can be kept in service.  A daily driver is a little different for most of us than a weekend warrior FE.  I personally would be pulling the heads and pan and checking bearings, and getting a valve job, as well as new timing set as a minimum.  Joe-JDC

Joe, you're good here! I fully agree one must find the root cause of why this happened. I'll add that if the engine has lots of miles, then yes, a teardown to the short block is a good idea as then one can determine how much more (or less) work and parts may be needed.