Oil pressure issue
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Junior User
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Oil pressure issue
Before I start, I can't find any threads where people are talking real numbers for oil pressure, instead of terms like "L,N and H."
I rebuilt a 1978 351w out of an econoline for my 1992 f150. Got the motor broken in and everything was great. I installed a mechanical oil pressure gauge in my truck and noticed that my oil pressure dropped to about 5 psi at idle when warm after quite a while. I'd go up to 40 at 3k rpms, so only idle was a huge issue.
I dropped the pan, changed the pump(figuring it was a cheap pump) with a melling, and noticed that my pickup tube had a bunch of crap in it, so I cleaned it and made sure everything was clean and crap free, slapped it all together and started it.
I didn't have time to let it get as warm as last time, but it dropped and held at 10psi at idle. I'm not sure if it will go lower over time, as it wasnt run that long.
Has anyone had a similar issue? Any ideas? The motor has all new bearings(main, rod and cam). Checked with plastigage and mains were the larger side of in spec, but still in spec.
Really struggling here. Thanks!
I rebuilt a 1978 351w out of an econoline for my 1992 f150. Got the motor broken in and everything was great. I installed a mechanical oil pressure gauge in my truck and noticed that my oil pressure dropped to about 5 psi at idle when warm after quite a while. I'd go up to 40 at 3k rpms, so only idle was a huge issue.
I dropped the pan, changed the pump(figuring it was a cheap pump) with a melling, and noticed that my pickup tube had a bunch of crap in it, so I cleaned it and made sure everything was clean and crap free, slapped it all together and started it.
I didn't have time to let it get as warm as last time, but it dropped and held at 10psi at idle. I'm not sure if it will go lower over time, as it wasnt run that long.
Has anyone had a similar issue? Any ideas? The motor has all new bearings(main, rod and cam). Checked with plastigage and mains were the larger side of in spec, but still in spec.
Really struggling here. Thanks!
Logistics Pro
Joined: Aug 2010
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From: Chillicothe
You said larger side of spec. How large is that?
What weight oil are you running? I know my tired 302 with darn near 300k on it runs 10ish at idle with 5-30 and 40ish at speed. With 15-40 it is 20 idle 50 at speed.
What weight oil are you running? I know my tired 302 with darn near 300k on it runs 10ish at idle with 5-30 and 40ish at speed. With 15-40 it is 20 idle 50 at speed.
Cargo Master
Joined: Mar 2010
Posts: 3,342
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From: Laramie, WY
What were your clearances? High side of spec may result in this. The mains, rods, and cam will all play a role. What was the crap in the pump pickup? Have you checked out the oil filter for debris? Any noises?
Hot idle, on the tight side of specs for bearing clearances, I see 30psi with 5W30 oil.
Hot idle, on the tight side of specs for bearing clearances, I see 30psi with 5W30 oil.
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The stock oil pressure warning is set for something ridiculously low. Like 6psi or 3psi. General rule of thumb is 10psi/1000rpm. You're probably ok. Get any lifter noise? Bearing noise?
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I dont have any noise, and I'm checking with a diagnostic gauge today to double check.
I was using Mobil 1 5w30, but I just switched out for mobil1 10w30.
Odd thing is that with the 5w30, my pressure would start at 60 cold, go down to 8 psi hot at idle, and get up to 40 under load.
The 10w30 started at 40psi cold, went down to 6 at hot idle, and wouldn't go past 35psi under load. Isnt that the opposite of what should happen?
I was using Mobil 1 5w30, but I just switched out for mobil1 10w30.
Odd thing is that with the 5w30, my pressure would start at 60 cold, go down to 8 psi hot at idle, and get up to 40 under load.
The 10w30 started at 40psi cold, went down to 6 at hot idle, and wouldn't go past 35psi under load. Isnt that the opposite of what should happen?
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Some stories I've heard over the years with strange oil pressure problems:
Oil filters can do some strange stuff but it's a stretch to think that's your problem. What are using for an oil filter?
Machine shops can make mistakes. They take out oil gallery plugs and orifices, clean the block before they install new plugs. They have been known to get it wrong.
Did you take the block for service? Have you talked to them?
If you send in an oil sample they can tell you if your engine is getting hurt, shedding metal inside.
You could check your oil temperature too. Pull the oil cap with the engine running and see if seems like there's oil getting to top end. Don't put anything in the hole, might not come back out.
Oil filters can do some strange stuff but it's a stretch to think that's your problem. What are using for an oil filter?
Machine shops can make mistakes. They take out oil gallery plugs and orifices, clean the block before they install new plugs. They have been known to get it wrong.
Did you take the block for service? Have you talked to them?
If you send in an oil sample they can tell you if your engine is getting hurt, shedding metal inside.
You could check your oil temperature too. Pull the oil cap with the engine running and see if seems like there's oil getting to top end. Don't put anything in the hole, might not come back out.
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