Low oil pressure .....

I have a 93 4.6 Lincoln engine with 93,000 on it and it has been maintained like it was a newborn baby since day one . Driven by an elderly gentleman who is pretty car savy . The engine has the weirdest oil pressure issues ...... it starts with no issues and oil pressure goes to 55-60 cold and as the engine warms at idle it drops down to 30 psi and stays . If you rev the engine a bit it will jump back to 55-60 . I figured this was pretty good for it's age knowing it's service history , but the gentleman I got this Lincoln TC from said it drops to 0 psi all of the sudden and the oil light and check engine light come on . He said if it sits for a few minutes it will go back up in pressure but after a few miles it will just drop off again ? He also said that when he checks the oil when it drops to 0 psi the dipstick shows no oil again until you wait a few minutes then the oil level on the stick comes back up to full . Where is the oil going ?? Is it staying up in the engine and starving the sump causing the a low oil pressure reading ? I'm stumped ........ any help or advice would be awesome .

On the '93 Town Car (as with most modern Fords) the oil pressure gauge is not actually a gauge at all. It is controlled by an oil pressure switch. If you have good oil pressure it should read in the middle of the "gauge". If the oil pressure is low, it will read no oil pressure.

I'd start by replacing the switch. If he's shutting off the engine when the pressure reads 0 psi, then immediately checking the dipstick, most of the oil will be circulating in the engine. Then, after a few minutes of the engine being off, the oil will drain back in to the oil pan and give a reading on the dipstick again. If he's checking the oil with the engine running, then I'd be surprised he would ever get a good reading.

-Rod

I should have mentioned that he had a mechanical Stewart Warner oil pressure gauge installed because he was not convinced that the dummy light was telling him the truth ( they are both hooked up to the engine ) I was wondering if the mechanic piped the mechanical gauge into the same area as the oil pressure switch ..... if that would make any difference . I would think that a real gauge would be telling what's actually going on with the oil pressure . I did take the gauge off and check it on my other car and it's working perfectly so I'm eliminating the gauge as faulty . The oil is always checked with the engine off . It's as if the oil is getting pumped in to the engine and at some point it does not make it's way back to the pan causing the pump to starve ? In all my years of wrenching on engines I have never run across this problem ...... oil always travels back to the pan . I'm wondering if there is something wrong with the head gaskets ? I know these engines do not have a lifter valley like most engines because of the overhead cam design so I'm guessing the oil has to run back down through the corners of the heads to get back into the pan or do these engine literally pump the oil back to pan ?

I'm not sure what the path of the oil back to the pan is.

Does the engine run well other than the oil pressure concern? If so, I doubt you have head gasket issues. There might be a sludge issue though that is slowing the oil flow back to the pan. Have you changed the oil filter and oil recently and checked the condition of the oil while draining? You could try substituting in a quart or two of transmission fluid and running that through the engine to clean out sludge and get passages open again. You won't want to run it this way for more than 100 miles or so though, basically just long enough to clean out the engine inside.

-Rod

The gentleman that gave me this Town Car also gave us his recently passed wifes 2000 Lincoln TC Signature which runs pretty good other than the fuel system is a bit mucky from sitting for two years . Anyway He has always had two or three of these Town Cars in his stable for as long as I can remember . So he is pretty good at keeping them all maintained on regular basis . The 4.6 that we are talking about is in a 93 TC and supposedly had the pan removed a few years back in trying to figure out the oil pressure issue , new pan gasket , filter , oil and I'm pretty sure he told me a while back that while they had it apart they changed out the pump ( not sure on that ) You asked if the car ran fine other the pressure drop ....... It runs like it is brand new , purrs like a kitten and has tons of power ..... at least while it's got good pressure , I don't want to run it to long because of the oil pressure issue so it has yet to make it around the block before I shut it down wait a few minutes and start it back up and get home again. I'll try the tranny fluid trick and see if that does anything ...... I guess I could run it the driveway for a while and monitor the pressure . Do you know off hand if the 4.6 has another oil pressure bung hole I could tap into just to make sure that the passage near the factory switch isn't plugged .

Sorry, I'm not familiar enough with that engine to know if there is another oil port you could tap in to.

-Rod

sounds like a sensor issue, have you tried Diagnostics to try and identify whats causing the spurious readings? I have heard good things about these.
http://www.amazon.com/gp/product/B008US9J9W/ref=as_li_tf_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B008US9J9W&linkCode=as2&tag=combooclu0e5-20";

The dipstick tells the truth regardless of the sensor. If the dipstick is showing no oil just after shutting down the car, then you have no oil in the pan.

My guess is that the oil is getting "stuck" in the upper end of the engine, which lets the oil pan empty completely, the pump is then sucking air and you lose oil pressure. Don't run the engine like this until it is repaired.

You MIGHT be able to fix this by removing the valve covers and finding the restriction, then removing it. I don't know the details of this engine (sounds like a V8), but there are usually holes in the cylinder heads that allow the oil to flow back to the oil pan, usually over the camshaft(s) to keep them lubricated as well.

If the cause is sludge, it might be possible to remove it with a solvent. There engine treatments that claim to remove sludge, some are run only with the engine idling, just to circulate the solvent in the engine at temperature and break down the sludge, then the oil & treatment are removed and replaced with fresh oil.

I'd first remove any sludge possible when the valve covers are off. Because chemical cleaners have limited effect, I would not presume that the cleaner could remove all the gunk in the hidden parts of the engine. If I found too much in the valve covers, then I'd consider if the intake and/or pan needed to be removed to get the rest of the sludge out.

However, if was manageable, then I'd use a strong solvent to clean it before changing the oil. Then I'd look for a treatment to add to my oil during oil changes to continue the cleaning process.

FYI, I once had to replace a camshaft because engine sludge that accumulated in the middle engine (on top of the block) and prevented the proper lubrication of the camshaft.

Thanks guys .... next time I get a chance ( maybe Monday night ) I'll pull the valve covers off . I've been wondering the same thing about the oil getting trapped in the upper half of the engine ....... The engine is a 93 4.6 Ford so there is no lifter valley so I'm suspecting the head drain oils .