Hello,

I have an usual situation with my oil pressure gauge dropping out after 10 minutes or so at idle. My sensor (sending unit) is a Motorcraft part and it is new. I have also repaired the wire harness to fix the issue with these engines where the harness get damaged by friction against the oil filter drip tray.

I understand (more or less) how the sensor and gauge setup works in that the gauge just shows that there is some minimum pressure and is not particularly quantitative. I have read many threads that suggest it is necessary to hook up a diagnostic gauge and read the actual pressure instead of relying on the difficult to interpret information provided by the needle on the console gauge.

This suggestion is quite a bit easier to make than to actually implement, as it turn out, though I think this would be a good deal easier on a 2WD model. I have, after several days of effort, managed to replace the sending unit with an analog gauge and collect some data which is listed below.

Code:

engine start: 75 PSI @ idle 900 RPM
              80 PSI @ 1500 RPM
              85 PSI @ 2000 RPM
      +2 min: 72 PSI @ idle 900 RPM
      +4 min: 70 PSI @ idle 900 RPM
          -> engine thermostat registers about here
      +6 min: 68 PSI @ idle 800 RPM
      +8 min: 60 PSI @ idle 800 RPM
              78 PSI @ 2500 RPM
     +10 min: 50 PSI @ idle 800 RPM
     +15 min: 45 PSI @ idle 800 RPM
              70 PSI @ 2000 RPM
     +20 min: 37 PSI @ idle 600 RPM
              65 PSI @ 1500 RPM
     +25 min: 33 PSI @ idle 700 RPM
              65 PSI @ 1500 RPM
     +45 min: 33 PSI @ idle 700 RPM
              65 PSI @ 1500 RPM

The pressure was almost 80 PSI at startup where the engine idles at around 1000 RPM. The pressure dropped steadily over the first 20 minutes or so, but the idle RPMs also drop to around 600 over that time. I assume that the pressure drop is due to the oil thinning as it heats up. The pressure never dropped below 30-32 PSI and always went up to 65 PSI or so when I ran the engine up to 1500 RPM.

Despite all the suggestions that this is the required procedure, I have yet to fine anyone who can comment on the above data and tell me if I have sufficient oil pressure or not. I have also not been able to find any references. There was a list that came with the gauge but it did not include the 4.6L engine from 2002.

Can someone tell me if the above data looks reasonable. It seems fine to be but that is just a guess.

Sorry that there is no clear pattern to the measurements but I was making it up as I went. I didn't have the proper set of connections to hook up the analog gauge and the stock sensor at the same time, so I couldn't read the pressure at the time when the sensor drops out. Based on the above readings, I would guess that the pressure is between 45 and 55 PSI when the console gauge drops out to 0.

LMHmedchem

 

Thank you very much for that information

I once left this running for more than an hour to charge the battery and only when I went to shut it off did I notice that the gauge had dropped out to 0. Later I started it up and found the pressure good. I sat there to see if it would hold and saw that it dropped out after about 10 minutes. Based on that, the engine had run for 50 minutes or so after the gauge said there was no oil pressure. The engine temp was fine and the engine sounded fine so I assumed that it was an instrumentation issue. I did need to check to make sure. Engine oil pressure isn't a good thing to assume.

Now I am left with the puzzle of determining the issue with the sensor.

Keeping in mind that the sensor is pretty new and is a Motorcraft part,

If the sensor is faulty, why does it work for 10 minutes and drop out?
- the needle doesn't flutter or anything, it reads solid good pressure and then drops straight to 0

The same question about the wiring, if the wiring is faulty why does it work and then not work?

I was concerned that my pressure was falling enough that the sensor cut out. I can rule that out now but I was confused that a rev of the engine up to 2500 RPM did not bring the signal back on the sensor after it dropped out.

Any ideas as to what is going on here?

Since the sensor seems to work for a relatively consistent period of time (~10 minutes) before it drops out, it seems like it would be a temperature issue. Offhand, I can't think of anything else that would change over a consistent time period like that. Can the sensor or wire fail if it is getting too hot? I repaired that wire harness and was careful to get it back in the original brackets and such but I guess it's possible I did something wrong there.

Other than that I really don't have very many ideas at this point.

LMHmedchem

 

Well I think I am done with this for now. I have come to the conclusion that the issue is that the oil pressure sender is overheating and this causes it to shutdown.

For some background about my suspicion that the sensor is overheating, my drivers exhaust manifold heat shield has crumbled. Ford does not make this anymore and I wasn't able to find any aftermarket parts available. I find this odd since I would expect that nearly every one of these that is still on the road is likely to need a new one by now. I thought about making one but I decided instead to look for a part from a later model Ford 4.6L engine that would still be available.

I ended up getting this one, which is for the 2009 4.6L Explorer,

Ford 6L2Z-9Y427-AA Drivers Side Exhaust Manifold Heat Shield

Other than the mount holes being in the wrong places, it seemed to fit fine. The cutout for the intermediate steering shaft was in the right place and after drilling some new holes it went on without issue. I drilled the new holes so that there was the same amount of space between the heat shield and the engine as there is on the passengers side.

My only thought at this point is that the heat shield does not fit well enough on the bottom resulting in a build up of heat in that area, which is where the sensor is. I only mounted the heat shield with bolts on the top, so maybe there are supposed to be some on the bottom, I don't know.

I think that the sensor is overheating because it consistently works fine for about 10 minutes and then dies. I can't think of anything that would cause this on a consistent time table other than heat, since the heat off of the engine should increase at a predictable rate at idle.

As a fix, I decided to fabricate a heat shield for the sensor out of 24 gauge galvanized sheet metal before putting it back on. This is what it looks like,

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I installed this with the open side facing down in the hope that if there was any excess heat coming off of the exhaust manifold, this would protect the sensor and allow it to keep functioning. It should also allow good airflow to the sensor once the truck is moving.

I installed this today and found some limited success. The oil pressure sensor kept functioning for 20 minutes (instead of the usual 10) before the gauge dropped out and the "check gauge" light came on. Though it is far from certain, I think this is good evidence that heat is the issue. I suspect that once I am driving, there will be enough airflow to keep the sensor cool. If I have a chance, I will try to add some reflective heat shield tape to the outside of the heat shield to see if that helps.

Whether or not the excess heat causes other issues remains to be seen. There is nothing much else in the area, so hopefully it will not.

I suspect that this is not a common issue since no one has replied to say that they have had the same problem. Still, I have attached a PDF template and instructions for the heat shield in case anyone else ever needs to make one.

Thanks for the help,

LMHmedchem