losing oil pressure
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Junior User
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losing oil pressure
I gotta 74 f250 witha 390. I was having some problems holding good oil pressure and installed a new oil pump. When I first start the truck, oil pressure will zing right on thop of the "I" in "OIL". This holds pretty good until it runs for about 15 - 20 minutes. Then it'll hang about the "O". Sometimes whe I come to the stop light it'll drop down so low that I'll have my hand on the key, ready to cut it off! Im stumped. I use Penzoil 10w40, new oil pump, new filter. Not sure what the operating temp is cause my temp gauge only works part time, and then I think it's iffy. Any one have any ideas??? I am stumped.
Posting Guru
Joined: Dec 2002
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From: missouri
Originally Posted by wckdclwn911
I gotta 74 f250 witha 390. I was having some problems holding good oil pressure and installed a new oil pump. When I first start the truck, oil pressure will zing right on thop of the "I" in "OIL". This holds pretty good until it runs for about 15 - 20 minutes. Then it'll hang about the "O". Sometimes whe I come to the stop light it'll drop down so low that I'll have my hand on the key, ready to cut it off! Im stumped. I use Penzoil 10w40, new oil pump, new filter. Not sure what the operating temp is cause my temp gauge only works part time, and then I think it's iffy. Any one have any ideas??? I am stumped.
Post Fiend
Joined: Jul 2003
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From: Spokane, WA
My 460 does about the same thing. Problem is with the stock guages it's so hard to tell what you're really looking at. I just installed an Autometer guage a couple days ago and found that while the truck is warming up I have about 60-70 pounds of pressure. Once it's warm (about 190 degrees for me) and I've been driving my pressure at idle will drop to 20 pounds or so. Now sure if this is too low or not but 20 pounds is the same point at which I had "0" on the stock guage, so it's kind of misleading.
Maybe I need to check on replacing the switch?
Maybe I need to check on replacing the switch?
Postmaster
Joined: Nov 2003
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From: Cab of a truck
I was told by a mechanic that lives down my road about oil pressure, that as long as you have 10lbs for every 1000 RPM you are ok. I would suggest installing a mechanical oil pressure guage also. Thats what I did. The '
high' and 'low' on the stock one just aint good enough.
high' and 'low' on the stock one just aint good enough.
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Joined: Jan 2002
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hehe if you do a search you will find lots of posts about this. If I remember correctly, some people will go as low as 6-7psi with no problems. I went through the same scare when I got my truck. I got a manual gauge, changed the weight of oil I was using, and did a few premature oil changes to try to flush our some of the accumulation.
I now get about 60-70psi when cold, and typically maintain 20-40 around town, and when I get on the freeway and get everything good and hot I will drop to about 10 at idle and about 20-25 at speed.
I would recommend a 270 degree sweep for the needle on the mechanical gauge. You are able take a more accurate reading. I started out with a 90 degree sweep and when hot it almost looked like it was reading 0, so Iwas not much better of than with the stock gauge
I now get about 60-70psi when cold, and typically maintain 20-40 around town, and when I get on the freeway and get everything good and hot I will drop to about 10 at idle and about 20-25 at speed.
I would recommend a 270 degree sweep for the needle on the mechanical gauge. You are able take a more accurate reading. I started out with a 90 degree sweep and when hot it almost looked like it was reading 0, so Iwas not much better of than with the stock gauge
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Posting Guru
Joined: Jul 2001
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From: Gainesville, FL
All,
I've owned a few of these and they all do the same thing. I have a theory.
What if the voltage drops at an idle. This, in turn, throws the voltage regulator for the gages off, and cause the gage to read low. What do you think? If so, why doesn't the temp gage and gas gage read low? Or do they?
It seems to me, that my oil gage responds the fastest. The fuel the slowest.
Chime in on this. Tell me what you think?
Secondly, Oil gage sending units are vibration sensitive. Has anybody ever changed a sending unit, to have it work well for a week or two and then start to do the same old thing?
KingFisher
I've owned a few of these and they all do the same thing. I have a theory.
What if the voltage drops at an idle. This, in turn, throws the voltage regulator for the gages off, and cause the gage to read low. What do you think? If so, why doesn't the temp gage and gas gage read low? Or do they?
It seems to me, that my oil gage responds the fastest. The fuel the slowest.
Chime in on this. Tell me what you think?
Secondly, Oil gage sending units are vibration sensitive. Has anybody ever changed a sending unit, to have it work well for a week or two and then start to do the same old thing?
KingFisher
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Post Fiend
Joined: Jul 2003
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From: Spokane, WA
I don't think voltage has to do with the oil pressure/guage problem. If this were the case it would do it when you first start the truck but it only seems to happen when it's warmed up. Also, I installed a mechanical guage and I'm seeing the same exact thing. I think that the stock Ford guage doesn't register much lower than 15 or 20 pounds so when you drop down there after warm up it looks like you've got zero.
Junior User
Joined: Jan 2004
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the gauge ( not a gauge but an idiot light ) on my 79 460 f150 always when i come to a stop does the same thing accept being a light it just comes on, most of the time i'll be stitting there and the lights just flickering and other times its on nice and bright me i thought its was a bad sending unit until one day out curiousity desided to cut open my oil fillter and discovered very very small bits of copper not alot but just enough to see it in a few areas
Moderator
Joined: Dec 2001
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From: Louisville,Ky.
I'll run her until she blows. I had a 71 Torino GT with a 351C that held 3-5psi at an idle and about 20psi @ 5500rpm. I drove it for over 3 years like that and it never came apart. The lifters were a little noisy (sounded like it had solid lifters @ about .012 lash)
When I finally tore it down, one of the main bearings had overlapped about 1/4". They were thin!! The crank wasn't even scarred. That made me a Ford guy for life!! Ford Tough
When I finally tore it down, one of the main bearings had overlapped about 1/4". They were thin!! The crank wasn't even scarred. That made me a Ford guy for life!! Ford Tough
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Alright fellows, here we go. Gotta sunpro gauge kit (270 degrees). Ive got about 20 psi when started up cold. Running down the Highway (No tach yet so not sure about rpms, 4sp with granny gear) it'll stay about 20. After it heats up to about 170 degrees, I notice that at a complete stop, probably idling at 800-1000, Itll go down to about the 5 pound mark. When I let out of the clutch itll tap on 0 until the rpms get back up a little. If I juice it at a light, itll swing from 5-20psi. Like I said before, I just put a oil pump on it a couple weeks ago. I did find that my fuel pump was spraying fuel everywhere when I was hooking up the oil gauge. Went and got a new one last noght and put it on also. It was junk,(Thanks "Jesse James") bad spring that fell somewhere in my motor! Hop its in the oil pan now, but got another one this morning and put it on before I found out all this other stuff. Soooooooo what do yall think, take the oil pump back to just to make sure? I hate pulling the D#$% oil pan back off, though. What about the weight of oil Im using. 10w30 in there now.
Moderator
Joined: Dec 2001
Posts: 22,436
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From: Louisville,Ky.
Is there gas in the oil? Many times when the diaphram goes bad, it will pump gas into the oil too.
Try 10w40.
Did you replace the pick-up tube too? It could be full of build-up or isn't sealed at the pump letting it suck air.
If all is good there, you probably have too much bearing clearance. No resistance, no pressure.
Try 10w40.
Did you replace the pick-up tube too? It could be full of build-up or isn't sealed at the pump letting it suck air.
If all is good there, you probably have too much bearing clearance. No resistance, no pressure.
Last edited by LxMan1; Apr 9, 2004 at 10:08 AM.