I have a 2003 F-150 with a Romeo 4.6L with 200,000 miles on it.

I have been having an issue with my oil pressure for the last couple days now that has me worried.

Sorry it's a long story but more info always seems to be better than less.

Backstory:
Live in Michigan (cold obviously)
I parked my truck for about a month due to a lot of work trips. Before parking it I had no issues with oil pressure. I went to start it a few weeks back but the battery was dead. I tried jumping it and there was a lot of cranking without it starting and finally had to bring the battery inside and charge it over night. Finally got truck to start and decided to drive it a bit before the work week and blow it's nose. During my trip the oil pressure gauge dropped and the light came on. I shut the truck off right away and coasted a bit and tried starting it again. It started and had "Normal" oil pressure. I continued driving and it did it again. Shut it off again and started it again. This went on for a few minutes until I made it back home. I thought that the oil needed to be changed from it sitting for so long plus it was time. I added a can of seafoam before I changed it and ran the engine for 10 min. Drained the oil and ran one quart of clean oil through and allowed it to drain out the last of the dirty oil. Installed a new filter(the old filter was a valvoline filter from the quick lube place...Junk?), added new oil and a bottle of the Lucas oil additive. Started the truck and it took a while before the oil pressure got to normal. Took it for a drive for about 15 min and everything seemed fine. I got a block away from home and the oil pressure dropped again. I decided to install a mechanical oil pressure gauge and check the pressure. I started the engine and the oil pressure went to 50psi and took it for a drive and after it warmed up a little it settled at 25 psi. The pressure would rise with higher engine speed and drop with lower engine speed but never more than 50psi and never less than 25psi. I figured everything was ok and called it a night.

I drove the truck the next morning and kept an eye on the oil pressure during my 50 mile trip and watched it slowly drop to 25psi while doing 75mph and 2200 rpm constant engine speed. Idecided to pull off and check the level and when I did the gauge was hitting between 0psi and 20 psi. I checked the level and it was just above a quart low most likely from the loss of oil when I hooked up the mechanical gauge. Added oil and the pressure went back to 50psi when I started the engine. The oil pressure sat at around 30psi on the freeway again and didn't really move the rest of the trip (apx 25 miles). Shut the truck off and it sat for around 3 hours. Headed back to my office and about 20 miles away it starte dropping in pressure again to 20psi on the freeway and hitting 0psi when I came to a stop and popping up and down. I stopped at my house and let it sit for about a half hour and when I started it again it was at 50 psi again and sat at 25psi the rest of the way into work.

What should be my next step? I was planning on changing the oil again just to make sure all the old oil was out and to let it work a little to flush it out but if I am going to need to drop the pan I'll wait till after that to do it.

 

The first thing you need to do is change the oil again but this time skip the Lucas crap. It's now part of your problem. Frankly, I wouldn't use that junk even in a beater. Refill with 5w-20 oil and use a quality filter like a Purolator or NAPA. Your most likely issue is the pickup screen is sludged and you'll need to clean it. The 5w-20 may buy you some time but the best way to clean it is removing the pan to clean it. If the 5w-20 gives you decent and consistent pressure that does not fall below 10lbs, then I would suggest running 2 doses of Auto-Rx thru it. Auto-Rx is a lanolin ester like the esters that were used in PAO synthetics about 15 years ago. It is a fabulous cleaner and will also provide seal swell if any are leaking. I doubt one dose will completely clean it but if you're on a budget, it certainly will help with one dose.
http://www.auto-rx.com/

Don't pay any attention to the claims on the website. It's a great cleaner, nothing more. It won't cure aids and it won't make you win the lottery but it will safely and slowly clean your engine without doing damage like a solvent based flush.

 

Ok new info:

Changed the oil again(no flush yet) Replaced my filter again with a WIX filter.

Oil pressure was 75psi when I first start the truck. Drove the truck for a bit and it settled down to 50psi and fluxuated with engine speed like it's suppose to. If I keep the rpm's below 2200 the oil pressure is fine. As soon as I take the engine speed above 2200 for a long amount of time say during a passing situation, the pressure drops to 25psi and when I let off it drops even further to close to 0psi. The only way to get the pressure back is to shut the engine off and allow it to sit for 30 seconds to a minute and then when I restart the pressure goes back to 50psi and acts normal until I do the above manuver again.

I'm thinking the bypass valve is sticking and causing the oil to dump back into the pan.

 

I'm thinking your cyl head drainbacks may be sludged up and partially blocked. A lot of this engines oil gets pushed to the cyl heads to feed the lash adjusters. At higher speeds/RPM's even more does. It may not be able to drain back to the pan fast enough to supply the pump. Once you let it sit the oil has time to drain down into the pan and you start the process over again.

 

A guy on the Dodge Magnum board has an oil pressure problem when his engine revved up. I suggested sludge was blocking the oil drain holes. He removed the engine pan and found that the oil pump suction screen was almost completely blocked like Labnerd said.

It does sound like your engine has a sludge problem. How long have you owned it? If you bought it recently from a dealer, they may help you if they sold you a sludged up engine.

I worked with a guy who bought his daughter a Toyota Camry with about 40k miles from the yota dealer. It started burning oil and they found out the engine was full of sludge. They replaced the engine and went after the person who had leased the car. He was contractually obligated to service the engine and they had a case.

 

Yea, clean the pick-up tube screen, -tomorrow. Call around, see who carries AutoRX. Use that after for the rest, that's good stuff. But yea, I wouldn't mess around,- definitely pull the pan on that one, I'm not sure you have the time for anything else at this point.

How did you get Labnerd & Dynotech helping lol. - Your lucky,- listen to them.

Good Luck.

 

Toyota/Lexus have had a lot of problem with sludged engines, even with excellent maintenance. They didn't have adequate crankcase ventilation and especially when they were driven short trips, they never burned the moisture off and when mixed with the oil, it did a great job of creating sludge. They are not the only ones who has had sludge problems in recent years.

 

Well so far after my last oil change I did two days ago the truck has been acting like it should.

I have been driving it gently for the last couple of days due to no other choice and it seems that the oil is doing it's job and cleaning up whatever the problem was. The oil pressure never drops below 25psi and the highest I have seen is 80psi on the first start in the morning. Cruising around it sits at 50-60psi.

I still plan on dropping the pan when I get the extra time and money just to make sure and I might even change the oil pump and the timing chain guides while i'm in there. I have always taken pretty good care of the truck and I have alway used synthetic oil in it so I know it can't be that bad inside the engine. I even had the heads off a few years back to fix a blown out spark plug and the heads only had a slight tint of brown to them.

Thanks everyone for your help and oh yeah...FRAM SUCKS!

 

I heard that the coolant passages in the heads were too small because they were trying to keep the heads hotter for cleaner burns and lower emissions and the heads were so hot that they were cooking the oil. But, I don't know that much about it. Just what I heard.

 

*ha mess up wrong thread*