I am having an oil pressure issue on a 2000 F-150, 4.6L.

I recently put a new set of heads on the motor because of some valve damage. Anyways. The oil pressure gauge in dash would sit at around 3/4.. Drive it a couple miles and everytime you would get back to idle (stop sign) it would drop to zero and the light would come on.

You could also hear it make a little noise like the top end wasn't getting oil. (Didn't run at idle long..)

I figured it was obvously starved of oil so I put a new oil pump, timing chains/guides/tensioners on. (Which I probably should have done with the heads.)

Same issue resulted, but no funny noises when the gauge drops off.

Suspecting that the sensor may be faulty and the dash gauge being useless anyways, I dug an old mechanical gauge out of a box and installed it. I'm getting similar oil results. (Under 25psi it seems.) I'm not sure if the gauge has just gone to crap over the years of being in a box. However, the previous low-oil pressure issue seems to confirm it's not the gauge.

I cleaned the oil pickup when I had the motor apart. It didn't seem dirty, but I sprayed it out regardless. The motor looked fairly fresh when I had it apart. Bearings looked solid, cylinder walls even looked freshly honed. From what I hear, the motor was a low-mileage replacement.

So what could cause a low-oil pressure issue?
Bearings seem fine, oil pump is brand new. Any idea's?

 

Correction:
35-40 PSI cold.
Under 25psi warm.

 

What pressure are you expecting ??? Your sensor probably is an on-off switch set at 8 psi. Any reading 0-7 psi will register as ZERO.. Any pressure 8-30 psi will read 1/2 scale or a little higher. It is not a gauge it is an on- off meter. 30 psi at idle should be GREAT !

 

More than that.. I edited the above post.

I'd think it should be running at 40+ warm. With a new pump is expect at least 60 cold..

 

I checked mine with a mechanical gauge a few years ago.
I can't remember what it was at 1500 rpm but it did pass spec.
Hot idle was around 20 psi.

 

After it warms up- it drops to zero on the gauge. If you unhook the gauge, it barely trickles oil out of the line. At 50-55psi cold today. Drove it maybe a total of 8 miles, gauge dropped to zero. It's like it's not even pumping oil to that area.

Is there any mechanical by-passes or anything that might stop oil flow? It's a brand new oil pump, driven by the crankshaft.. I would think it should have oil pressure no matter what. The fact that it's doing exactly what it did before the new oil pump is telling me it has to be a problem elsewhere. But unless someone can point me in the right direction, I have to assume bearings. Right?

 

Idk Prozon
You say the main/rod bearings looked good?
There should be some sign of brass in the oil if the
bearings are bad enough to drop oil pressure to zero
Try a steady 2000 rpm with no load when hot, you should pick
up a rattle if rod bearings are the cause
Not sure if a leaking timing change tensioner would do it,maybe excess camshaft journal clearance?
hopefully someone else will chime in with a better
outlook
good luck keep us posted

 

If the oil pressure was o.k. prior to the valve damage, and now low after you did the heads.... im guessing the problme is in the top end, not the bearings. You seem to have pressure at high rpm, but not low rpm ? That sounds like you have a hole / excessive clearance / excess leakage at some point. As you speed up, the volumn over rides the leakage and you build up pressure.

 

You sure have an issue because my 203k mile motor idles at hot 25 psi, runs near 50 psi at cruise and goes as high as 75 psi cold start.

Run through the whole reason you took things apart and what you did.
Was oil pressure ok before the work?
.
Oil pumps usually have a pressure relief spring loaded ball
If it's not there or stuck open this can be the result.
Since the cam timing chains depend on oil pressure, lack of chain tension can allow chain slap on the case cover and possibly other noises in the valve train.
Good luck.

 

Is this a mechanical (fluid ) gauge or electrical? I'm assuming mechanical as you said trickled out, have you inspected the entire line for any kinks, blockages, etc to eliminate the simple stuff and have you tried attaching the gauge as close to directly on the motor to eliminate line damage and do you still get the same low reading?. Was the oil ports confirmed clean when the heads etc were done and you don't have a surprise in there somewhere. And I will agree it should be higher I am changing my gauges just out of preference but my oil gauge will read 3/4 on a cold start and remain there the entire time truck is running and yes the gauge works fine a fluctuating oil gauge is cause for alarm in some form or another.

 

I agree with this- but where could there be excessive clearance causing oil pressure issues other than a bearing? I think that has to be the case, sadly. I was hoping there was some crazy magic Ford off switch for oil pressure and I could just flip a switch and fix the issue. Lol.

The oil pressure never showed up as low on the stock setup- which seems to be accurate as far as none/some. Other than the damage to the head, there wasn't' any other issue. It just lacked power. Upon pulling it apart, I discovered the bottom end being minty fresh, and decided to put some heads on it. It ran fine for the first week- and then it developed an oil pressure issue. I'd say it had about 300 miles on it before developing the low oil pressure. The heads were sent to the machine shop to be checked out and a full gasket kit was installed on the motor.

I had thought the oil pump was the issue causing this- I changed the pump and not wanting to have to tear it apart again, I changed the tensioners, chains and guides. I don't think they are the issue as the problem did not go away- nor did it get worse.

I used a gauge with one of the clear nylon lines. I ran it to the port for the oil pressure sensor- and I only had about 8" of line, so there's no chance of kinks. As the gauge had results that would seem to mimic the stock dummy gauge, I had used the gauge on another car of mine and it worked flawlessly there, I don't think there was an issue with it.

The heads were from a cop car- 80k on them. I sent them to the machine shop to be machined flat and everything checked out. I looked over and cleaned up everything when reinstalling it all. I had the motor out- so the likelihood I missed something is a lot lower then if I was trying to do it in a dirty engine bay.

The stock oil gauge is just an on-off gauge. If you have no oil pressure, it will read none. If you have any at all, it will read 3/4. Kind of a stupid setup. (I actually think the stock gauge kicks in at like 7.5psi or something.) I just put the stock sending unit back in. 700rpm's, oil light on. 750+, oil light off.

I'm stumped here. I think i'll throw some of that really thick Lucas oil treatment in it and run it til she blows up, unless of course someone can think of something else. At least with the Lucas oil in there, if it's not pumping oil at low rpm's it will stay lubricated lol.

Thanks for the input everyone, i'm open to more suggestions/guesses.

 

At this point I would have to agree with steve, your other option is a special K&N oil filter that has a special valve in it to help regulate your oil pressure but if it is tolerances this will not help you. Here is a link if your interested in the filter option ( http://www.knfilters.com/oil_filters.aspx )

 

Maybe a dumb question, but did you check that the screen on the oil pick up tube was clean??

 

Oil pickup is clean.

I was going to pop a vacuum line to make it rev higher at idle- but the ones I tried dropped the idle lol.