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Car Forum / Ford / Ford Trucks / March 2007low oil pressure
Hi guys I have a 1977 F-250 with a 400M in it. The motor was redone two years ago about 40,000kms. The oil pressure gauge always read in the middle at idle and just off the high mark when going down the highway about 2300RPM. Then about a week ago I noticed the gauge reading almost nothing at idle and only about half way at highway speed. I put an oil pressure gauge on it and it read 4psi at idle and 30psi at 2000RPM. What happened has my oil pump finally kicked the bucket or are my bearings wore. I just don't understand how bearing wear could drop the pressure so much in only a week when it has been awesome for so long. Somebody please help me I losing my mind with this truck!!!! > Hi guys I have a 1977 F-250 with a 400M in it. The motor was redone > two years ago about 40,000kms. The oil pressure gauge always read in [quoted text clipped - 7 lines] > awesome for so long. Somebody please help me I losing my mind with > this truck!!!! The only way your going to know for sure is with a tear down. Possiblities, Easy first fix attempt, change the oil filter, bypass could be stuck. stay away far far away from Fram. Motorcraft FL1A and FL1HP are made by Purolater.. Wix very good, high end NAPA good, AC Delco Durogaurd excellent. Purolater run hot and cold. Autozone filters junk, Bosch made by the same out fit, as well as Deutsch, STP and Champ. http://people.msoe.edu/~yoderw/oilfilterstudy/oilfilterstudy.html must read site if you care about your engine, a real eye opener. Oil could be contaminated, change it when filter changed, and I know you prefill the filter before you install it right? oil pump pressure relief valve partially stuck open. Main bearing failure, partial bearing spun restricting oil hole. cam bearings washed Pick up screen blocked. does the engine start with a) normal pressure and then loose it, or ib) s it low right from the get go cold? A) could point to blocked oil return holes resulting in the pump sucking air (slim possiblity, engine should rattle like hell, lifters make an unholy noise) Whitelightning On Feb 26, 7:56 pm, "Whitelightning" <white.lightni...@verizon.net> wrote: > <andrewhetheringto...@hotmail.com> wrote in message > [quoted text clipped - 31 lines] > > Whitelightning Hi there I have two questions and that is if hte main bearings were spun how could the pressure be low would it not be higher because of restriction. My second question is what is the oil pump pressure relief valve please explain. And when I start it the the pressure does not move on gauge although there is 4psi of pressure at cold or hot idle, no knocking whatsoever though. Thanks for your prompt response. > Hi there I have two questions and that is if hte main bearings were > spun how could the pressure be low would it not be higher because of > restriction. My second question is what is the oil pump pressure > relief valve please explain. And when I start it the the pressure does > not move on gauge although there is 4psi of pressure at cold or hot > idle, no knocking whatsoever though. Thanks for your prompt response. Ok, if you spin a main bearing, ti will significantly increase the gap between the crank and bearing after a very short time, due to no lubrication for that main. Hence the oil flows out unabated.. The oil pump pressure relief valve is used to bypass the oil filter on especially cold mornings or in case the filter becomes clogged. This will ensure lubrication to the engine regardless of it being filtered or not... Some oil (filtered or not) is better than no oil. Like Whitelightning said, older engines are notorious for low oil pressure at idle, but as long as you have SOME oil pressure (4-10psi), it will be fine. You have stated 30psi at 2000rpm, and that is well within the pressure range for that rpm.. Ford Tech >> Hi there I have two questions and that is if hte main bearings were >> spun how could the pressure be low would it not be higher because of [quoted text clipped - 18 lines] > >Ford Tech What weight/grade of oil are you using and how often have you been changing it? ----------------- TheSnoMan.com > Like Whitelightning said, older engines are notorious for low oil pressure > at idle, but as long as you have SOME oil pressure (4-10psi), it will be > fine. You have stated 30psi at 2000rpm, and that is well within the > pressure range for that rpm.. > > Ford Tech Old school rule of thumb: 10 psi per 1000 RPM = OK RCE > The oil pump pressure relief valve is used to bypass the oil filter on > especially cold mornings or in case the filter becomes clogged. This will > ensure lubrication to the engine regardless of it being filtered or not... > Some oil (filtered or not) is better than no oil. all most right, but not quite. The bypass on the oil filter will let oil bypass if pressure gets to high for any reason. The oil pump pressure relief valve dumps oil back in the oil pan. I've seen them get stuck open partially by a piece of garbage or just wear, I've seen the spring in the valve break not seating the valve properly. It's part of the oil pump. Given everything being stated, the sudden loss if I read corect, the lack of noise, it could be the pump. But since the oil pan has to come down to get to it, might as well platigauge the mains and rods while the pan is down. I've polished crank journals using emmery paper and leather thongs before and then rolled a set of bearings in slightly over size.. (Dang dating myself again) Whitelightning minimum oil pressure is mostly controlled by the condition of the cam bearings, after that the mains. The 351 modified and the 400 were notorious for having a worthless oiling system. If you're seeing 30 psi at 2000, then I'd just drive it. Oil pressure at idle is not critical as long as there is some.  SignatureSteve Barker > Hi guys I have a 1977 F-250 with a 400M in it. The motor was redone > two years ago about 40,000kms. The oil pressure gauge always read in [quoted text clipped - 7 lines] > awesome for so long. Somebody please help me I losing my mind with > this truck!!!! Once you understand that the oil pressure is achieved simply by the restriction caused by the "small" clearance between your bearings. No matter what is going on with the pump, without restriction, you will not have pressure. Not unlike placing your thumb over the end of a garden hose. If your bearing surfaces wear (for whatever reason), the clearances get LARGER, not unlike lifting your thumb from the end of the garden hose, and the oil pressure drops. Your oil pressure loss could be from worn bearings or a failing oil pump. It takes almost no time for an under-lubricated engine to chew itself up. In any case, you should NOT run an engine with no oil pressure. Good Luck > Hi guys I have a 1977 F-250 with a 400M in it. The motor was redone > two years ago about 40,000kms. The oil pressure gauge always read in [quoted text clipped - 7 lines] > awesome for so long. Somebody please help me I losing my mind with > this truck!!!! None of the manuals I have give an oil pressure spec at idle, but all of them covering those years say 40-65 psi at 2000 rpm. I would say at idle hot should be 15-20 psi. Someting is going on in the engine. My really old manuals ford says 40-65 psi depending on model at 30 mph , course thats going back into the late 50's to mid 60's.. Are you getting lifter/valve clatter? 4 psi isnt enough to pump the lifters up. Whitelightning SNOman brought up a good point. The weight of the oil. The last 400 I had, I ran straight 50 in it to keep the light off at idle. SignatureSteve Barker > Hi guys I have a 1977 F-250 with a 400M in it. The motor was redone > two years ago about 40,000kms. The oil pressure gauge always read in [quoted text clipped - 7 lines] > awesome for so long. Somebody please help me I losing my mind with > this truck!!!! On Feb 26, 7:30 pm, andrewhetheringto...@hotmail.com wrote: > Hi guys I have a 1977 F-250 with a 400M in it. The motor was redone > two years ago about 40,000kms. The oil pressure gauge always read in [quoted text clipped - 7 lines] > awesome for so long. Somebody please help me I losing my mind with > this truck!!!! Well thanks for the help guys but I got it figured out tonight. It tunrs out that the oil pressure sending unit was no good and with the new one installed the gauge reads at the halfway mark at idle and just of high at highway speed. So I guess it was a false alarm.Sometimes the answer is right in front of you after all. Thanks again to everybody's help it was good to learn something anyways. > On Feb 26, 7:30 pm, andrewhetheringto...@hotmail.com wrote: >> Hi guys I have a 1977 F-250 with a 400M in it. The motor was redone [quoted text clipped - 15 lines] > the answer is right in front of you after all. Thanks again to > everybody's help it was good to learn something anyways. What happened to the "I put an oil pressure gauge on it and it read 4psi at idle and 30psi at 2000RPM"? That 4psi is awfully low... >What happened to the "I put an oil pressure gauge on it and it read 4psi at >idle and 30psi at 2000RPM"? That 4psi is awfully low... Yes, there is a conflict here because a direct gauge is a more trusted reading than a remote sending unut. ----------------- TheSnoMan.com > On Feb 26, 7:30 pm, andrewhetheringto...@hotmail.com wrote: >> Hi guys I have a 1977 F-250 with a 400M in it. The motor was redone [quoted text clipped - 15 lines] > the answer is right in front of you after all. Thanks again to > everybody's help it was good to learn something anyways. Is the oil pressure gauge an exact replacement for the original? Many of the new oil pressure "senders" used in newer cars and trucks are simply a go/no-go switch rather than a linear gauge. As long as there is enough oil pressure to actuate the switch, the meter reads normal and does not reflect actual changes in the oil pressure. RCE >> Well thanks for the help guys but I got it figured out tonight. It >> tunrs out that the oil pressure sending unit was no good and with the [quoted text clipped - 10 lines] > > RCE If that's the case, the dash gauge wouldn't vary with engine speed, as the OP says it now does. |
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