1999 Expedition 5.4 V8 4x2 155,000-ish (odometer doesn't like to work) miles. Fluids checked weekly, I'm poor but I do the best I can with keeping it running. It has never used oil before, but threw a code for the #4 COP to be replaced (started shimmying and shaking at around 45mph, turning overdrive off seemed to help some) I bought the part and was going to do the replace on it over the weekend...on the way home it starts just..KNOCKING, it sounded like the damn thing was going to come apart before I could get it pulled over. Got it off the road and because all the gauges go batcrap crazy constantly I realized "hey, maybe that check oil light wasn't actually kidding? The damn thing (oil gauge) goes to 0 then back up to regular pressure off and on just like the gas gauge...anyway I got it in my head that I had a stuck lifter, went to check the oil thinking I could add some lube and NO OIL...and there was no puddle when I moved it that morning, some minor burning smell when I opened the hood to discover this. If I fill it back up with oil the knocking calms down a lot but the oil disappears, and now its started being really hard to start, I have to hold it to 2k rpm just to get it come to a smooth idle (only did this once to make sure it would actually still start). I'm not a car geek, I've been learning as I go with this thing from necessity and a chiltons manual and I don't have the money for a mechanic to take a look and tell me for sure, but does it sound like the head gasket is deteriorating? I really need to keep this running for at least another six months, I'm a single Mom with 4 kids and this is our only transportation....is there anything I could be missing? I checked the oil drain plug and it looks fine.

Thank you to anyone for any advice or help, feel free to laugh at me...there is no better learnin' than the hard way....

 

Welcome to the site..

Sounds like you have more than one issue, and putting the others aside, the oil pressure/knock or disappearing oil would be the most critical if it drops from a normal level on the stick to no indicated oil in a short time.

If you top of the oil to the correct level on the stick, and if the oil level drops fairly quickly (even within days) you'd almost have to have a major leak. Even a moderate leak would/should show somewhere with some driving time, hangings drips, oil tracking, puddle, smoke etc. No engine oil inside the coolant reservoir?
The 5.4 doesn't have a low oil sentinel or pressure shut off, so even if it were low on oil it should still start, and would run to its destruction without oil.

Same with a bad COP, unless there were 'multiple' failures, it should still start but would run rough.

If it were run out of oil (not just low on the stick if that's what your seeing) and damaged the base engine (depending on what your hearing as far as noises 'now'-calms down a lot?) , first check should probably be an oil pressure test through the pressure sender port with a mechanical gauge. If the pressure tests bad, probably no point on moving forward with the other complaints. Sometimes if an engine is run out of oil a test sample of the remaining oil in the pan may show suspended metals in the oil or metal bits on the drain plug. If any abnormal debris is present, may indicate an engine failure. If prior to the low oil condition the engine sounded 'normal' and now has any significant knocking/clattering a good bet would be to make sure no damage was done if in fact it was run dry,, and that the oil gauge bounce was 'only' the gauge.

 

Thanks Hayapower, I didn't even know to check the coolant reservoir , I'll do the oil pressure test today and see if I can get anything out of the pan that indicates bad juju.

 

I think it may be time to trade that thing in for something a little more dependable. usually when you hear a knocking sound due to little or no oil pressure the bottom end is about come loose and that ain't good. the one thing that indicates a head gasket is they usually overheat rather quickly or you get water in the oil and vise versa plus it misses something awful.