Low oil pressure when temperature is reached

Tiny
RANDYFAUTEUX
  • MEMBER
  • 1997 FORD F-150
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 100,000 MILES
We had the issue on a prior motor. I ended up with a blown motor due to low pressure. I bought a new motor from a junkyard, same issue. I connected a gauge to the motor to see and at startup I get 70 PSI and as it heats up the pressure drops to 0 PSI. Drain ports are clear. Tried using 10W30 oil, it calls for 5W20. At first I had a premium oil filter and only got 60 PSI at startup and the drop was faster before it got to temperature. The bearings looked great, as well as the engine internals all looked clean, as it seemed the engine was well cared for. At a point where I cannot figure anything else out.
Saturday, March 13th, 2021 AT 6:57 AM

6 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Couple questions. First, this was the exact same issue on the other motor? If so, what parts related to this did you change over? Clearly the PCM is still the same but did you swap any sensors from your engine to this engine?

Also, are you hooking up a mechanical gauge to verify this is what the actual pressure is? Meaning if a mechanical (external) gauge says the same thing that this is dropping to 0 then we clearly have a mechanical issue.

https://www.2carpros.com/articles/high-or-low-engine-oil-pressure

Things that would cause your pressure to drop to 0 are blockage of the pick up, oil pump failure, sensor issue. Hence the need to find out what parts were transferred over and if this is an external gauge. Thanks
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Sunday, March 14th, 2021 AT 6:04 PM
Tiny
RANDYFAUTEUX
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  • 4 POSTS
Yes, I used a mechanical gauge. I didn't swap any sensors over and any parts related to the crank and cams were junk from my old motor so I couldn't use them. I had someone tell me that the bearings in the motor were bad and that I would have to do a total rebuild of the engine. I'm a bit disappointed because I learned the engine that I bought was from a 1997 F150 but, it was actually not an F150 4.6. I think it was one that came out of a Crown Vic and someone swapped over parts to fit into an F150.
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Tuesday, March 16th, 2021 AT 7:23 PM
Tiny
RANDYFAUTEUX
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  • 4 POSTS
Almost forgot. The Pickup tube was clear. The return ports were also clear, the oil pump we switched out with a new one and still had the issue. Which is why someone told us it was likely bad bearings.
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Tuesday, March 16th, 2021 AT 7:25 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
So at this point that is probably correct. The oil pressure is created by the pump pushing oil through the tight passages in the engine and bearings. So when the clearance is too large and the oil gets hot and thins out the pump can no longer keep the pressure up.

At this point, I would try using an oil thickener like Lucas oil stabilizer or similar. You will need to drain the some oil out and add this in or just change the oil and add the proper amount as it says on the bottle.

Also, I would be careful to just use thicker oil as in cold weather it will not protect as well. This additive is designed to operate in different temperatures.
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Wednesday, March 17th, 2021 AT 6:58 PM
Tiny
RANDYFAUTEUX
  • MEMBER
  • 4 POSTS
We currently have the engine out, once again, however not knowing what the new motor is actually from and pulling the bearings to look at them for a possible part number all I was able to find was a stamp F2LE-AD on the rod bearings and F1AE-AD on one of the main bearings. I tried to search online to see what bearings they are. The main one I felt some tiny scratches inside it so that is possible to be the culprit, trick now is going to find out what motor it is ex. Crown Vic 4.6, Mustang 4.6 or some other 4.6 Ford engine.
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Wednesday, March 17th, 2021 AT 8:27 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
More than likely a Ford dealership will be able to look up those and cross reference them. That is the beginning of the part number they go with.

Below is the crank part number out of a 4.6L Crown Vic. It is close but not correct.

Can you post pictures of the bearings and we can see if we notice anything? Thanks
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Thursday, March 18th, 2021 AT 6:38 PM

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