F150 Low Oil Pressure

[legion]

I just got into Florida an hour ago. My truck is having some "issues".

I have a '97 F150 with the 4.2L V6. As I was climbing some hills in Tennessee, the oil pressure would start to waver (this has never happened before). This would happen every time I climbed a long hill. The problem would go away when I filled up with gas.

As I pulled into the hotel in Georgia last night (parking uphill), the oil pressure dropped completely and the warning light came in. I started it up this morning, and it was fine the whole trip, until I was low on gas and climbing one of the causeways to get out to Merritt Island. When I got onto the island, the oil pressure would start to waver when I came to a stop light. The problem went away when I filled up on gas.

I replaced the oil pressure sensor last year (I had the problem once a year ago, replaced the sensor and it went away...until now). There are no oil leaks. I changed the oil in the truck the night before leaving for Florida.

Could I pretty much assume the problem is the oil pump?

Any ideas what one is going to cost to replace?

[legion]

Thank you all for sparing me information and instead giving me those ultra-helpful thread ratings.


Besides...I know who is behind it now.

[IROC]

Something seems fishy. If nothing else, I would check the oil pressure independently via a mechanical pressure gauge before throwing any money at it.

The correlation with a full gas tank has me stymied...

[tobster1911]

I assume that you check oil level and it was ok?

In my old '78 when the oil level gets low, the pressure gauge starts to bounce because the pickup in the pain is below the oil level.

+1 no idea why fuel level would affect this. Strange.

[Joeaksa]

If the pressure light AND sender is showing low oil pressure, then you have LOW OIL PRESSURE! Its usually two different sensors, so when one triggers thats a possible sensor issue but when both hit its time to become worried.

Have seen this in engines that did not have baffles in their sump but if you say the engine is full of oil that leaves something else. Wonder if the oil is having issues draining back to the sump? Climbing a hill... high throttle openings, no vacuum... something is going on here that we are missing.

Would love to see what a direct reading gauge says. Also have you cleaned all the wiring connectors to the sensors?

[Shuie]

Originally posted by legion


Besides...I know who is behind it now.

WHO??????

[VINMAN]

Chris, The oil pressure sending units in Fords have a tendency to go bad. In small blocks the oil gallery near the sender also can get gunked up. Both of wgich can give you a reading like you are getting. Another poosibility, which i have seen a few times, is the screen on the oil pick-up might be clogging up.

[legion]

I'm taking it to a mechanic tomorrow morning. I called the shop a relative takes his Ford truck to for work. He seemed to think it's a main bearing on the crankshaft.

If so, it looks like I'm buying a new truck while I'm in Florida. The cost of a bottom-end rebuild exceeds the value of the truck.

I've been checking the oil at every stop. The oil is new and clear, there is plenty of it, and there are no oil leaks.

[competentone]

Originally posted by VINMAN
Another [possibility], which i have seen a few times, is the screen on the oil pick-up might be clogging up.

Had that problem with my Ranger. Ford used just a silicon gasket on the oil pan; too much silicon was applied at the factory and the "ooze-out" on the inside of the pan broke off over time and blocked the screen.

The problem first showed itself with the oil pressure gauge being slow to rise on start-up with a cold motor. Cutting open the oil filter also revealed smaller particles of the gasket material that got through the screen on the pick-up.

If you have a blocked pick-up, the relationship you're seeing with filling the gas tank, may just be that the motor is shut down allowing a few pieces of gasket material (or whatever) blocking the screen on the pick-up tube to drop free allowing better oil flow when you re-start the motor.

Let is sit for a while, then drain the oil and filter it and see what you find.

[oldE]

I would follow Competentone's advice and check for debris first.
There might also be the possibility there is a bad ground condition in the gas tank guage sending unit. When you get to low fuel levels, (or gas goes to the back end of the tank while climbing hills) the extra voltage causes the oil guage to read low.
It has never happened in my (4.2) F-150, but I have experienced a similar problem when a solder joint in the instrument cluster of my Passat started to fail.
Good luck.
Les

[Jay Auskin]

You have a Ford that actually has a pressure "sensor"? Typically, Ford just installs a pressure "switch". They have a guage on the dash but it always reads right in the middle when the engine is running. Kinda a waste of a guage if you ask me? My Crown Vic is like that, as are the F250 diesel trucks.

[competentone]

Originally posted by Jay Auskalnis
You have a Ford that actually has a pressure "sensor"? Typically, Ford just installs a pressure "switch". They have a guage on the dash but it always reads right in the middle when the engine is running. Kinda a waste of a guage if you ask me? My Crown Vic is like that, as are the F250 diesel trucks.

In the 180,000 miles for my 1990 Ranger, I've had to replace the pressure sending unit twice (once for leaking, once for malfunction). At the dealer, there were two different part numbers for the sending unit, one if you had a guage, the other if you just had a light -- I assume the guage sending unit is a pressure sensor.

Maybe Ford has changed this on later models -- perhaps as a "cost cutting" measure, while still keeping customers who like a guage "satisfied."

Any update from Legion? Hopefully he's not along the highway somewhere with his thumb in the air?

[Joeaksa]

Chris,

What happened???

Engine still running ok?

Joe

[tobster1911]

Originally posted by legion
I'm taking it to a mechanic tomorrow morning. I called the shop a relative takes his Ford truck to for work. He seemed to think it's a main bearing on the crankshaft.

If so, it looks like I'm buying a new truck while I'm in Florida. The cost of a bottom-end rebuild exceeds the value of the truck.

I've been checking the oil at every stop. The oil is new and clear, there is plenty of it, and there are no oil leaks.

And why would filling the gas tank have any effect on this? Sounds fishy to me. Did they offer to buy the truck off you cheap? If it was a spun bearing, why would the pressure drop?

[rammstein]

Believe it or not, the RX8 has a pressure switch too! I couldn't believe they would fit something like that onto an expensive car. At lease have a light then, and not some faux guage misleading me into thinking its reading something.

Legion- Sorry I can't make it up to see you- work and all. You still gonna be there on the weekend? That I can do, it would be cool. Especially if you're truck shopping- thats fun. Let me know.

[legion]

I'm sitting at a Chevy dealership right now.

[notfarnow]

Well, I have no useful advice... but sorry you ended up having to deal with this crap while on vacation.

That sucks

[rammstein]

Can the salesman smell blood?

[SlowToady]

Originally posted by rammstein
Can the salesman smell blood?

Do Bears **** in the woods?

Legion, are you at the steal--er, dealership getting the truck checked out or looking for a new truck? Find out what's wrong with yours?

Sorry about your troubles, especially on vacation.

[rammstein]

I can't even fathom how badly this would go:

"yes, my current truck has died, and I NEED to buy a new one to get back home".