302 oil pressure

I just bought a 1931 Ford Town Sedan with a 1974 Ford Truck 302 engine. This engine was rebuilt about 4000 miles ago. I am getting low oil pressure readings so I replaced the electric gauge with a mechanical one. At start, the pressure is 40 psi cold. When driving it gradually goes down to 20-25 psi. At idle when warm, it is 5-10 psi at best. no unsaul sounds,

Here is what I am going to try:
1 change the oil filter (there is plenty of oil) Can a plugged filter cause this?
2. The oil pan was repleced by the former owner with a chrome pan. Could it be smaller than needed?
3. clean and/or Replace the oil pump
4 (I hope not) pull the engine and check all of the bearing clearances.

Any other ideas?? Thanks:confused:

i've ran into a similar problem on a 302 before... it turned out the previouse owner had put a high volume pump in with a standard pan.... so the pump would keep all the oil in the heads and pressure would read super low

A high volume pump won't affect the pressure once the relief valve opens.It takes a certain volume of oil to reach the pressure the valve is set for, after that the excess flow returns directly to the sump. They will increase the pressure at low RPM. That old yarn about the oil all ending up in the top of the engine is an old wive's tale. I've run lots of them and never had any problems.
302's aren't noted for lots of oil pressure. If it worries you, try a different brand of oil, some engines show a preference. There is a reason most engines have idiot lights nowadays instead of gauges.

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Originally Posted by carappraiser

Any other ideas?? Thanks:confused:

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Yeah, do all those things to make yourself feel better then stop playing the "more is better" game. You don't have a problem based on what you've described. Oil flow lubricates, not pressure.

That is a serious clearance problem somewhere. You could try draining out some oil, and adding a couple quarts of LUCAS OIL STABILIZER but it is a stop gap solution.

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Originally Posted by DennyW

All I'm going to say is, normal oil pressure is 40-65 lbs. You can take it from there. :LOL:

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Every factory recommendation I've seen states (at full op temp and at idle as the questioner here stipulated for his low numbers) somewhere between 5-20 psi depending on factory suggested oil vis and temp. I'd love to see any manufacturer specs you can come up with for passenger car engines that supports 40-65 at idle and full temp.

I just looked in my ancient 1973 Ford Shop Manual. For a 302, at operating temperature the expected oil pressure is to be 40 to 60 psig, the 351 is 45 to 65 psig. These pressure readings are at 2000 RPM. This particular manual doesn't specify an idle pressure though any Ford engine I have put together will run at the higher end of that scale (60 to 65psig), with 20 to 25 psig @750+/- RPM (mild camshaft). Below those figures there is something amiss - sender or gauge, oil filter, oil pump, crank/rod or cam bearings, plugged galleys to name a few potential trouble spots.:HMMM:

What if an oil galley plug came out, like one behind the timing cover???

Rocky

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Originally Posted by Rocky72

What if an oil galley plug came out, like one behind the timing cover???

Rocky

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If the engine had never been touched/opened, very doubtful. For whatever reason, Ford seems to want to put them in to never be removed. I usually use a long handle allen wrench (unless it is one of the 3/8" square pipe plugs) and a 2 foot piece of pipe to get them out. But not impossible.

My bet would be a tired oil pump (assuming you are sure of the filter, gage and sender). Pumps are cheap 20 to 30 dollars, plus a pan gasket and few hours of labor. If it is this, you need a pump, a new drive shaft (use an SVO high strenth shaft) and new oil pickup.

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Originally Posted by DennyW

If the splash system was so good, because it did give everything an oil film, why have they changed ?

With the higher output engines, I can guarantee you if you run 5 lbs, that motor will not last very long. :) Every oil pressure gauge I have seen, including factory installed ones, do not just go to 5 - 20lbs.

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Denny, interesting non sequitur that only demonstrates that you didn't understand my point when I wrote that before, and you've not done any research, as I know you often do otherwise, to broaden your understanding of what I've said. And unlike most of the answers that are made in response to this frequently asked/stated question/comment I'm not answering in absolutes (other than stating that having oil present is more important than evaluating on an arbitrary number without context), so the remark about a 5-20# gauge is wholey inappropriate.

Ireland, your experience supports my statement even though most would think it's a challenge (perhaps you included) as the bottom of your range of experience at idle is within the range I posted, albeit the top. We can pick nits about precise numbers, but that misses the point as well. Lubrication isn't just about the numbers on a gauge, it's about the lubricant being at the point needing lubrication.

Would I like to see higher numbers than appraiser has listed? Sure, but only from the perspective of having a greater safety margin. He's operating at the bottom of the range that my experience and training shows to be adequate.

This thread, and nearly every other one that's dealt with oil pressure, so it's not unique, does a total disservice to proper diagnostic procedure. Usually folks, who's intentions are to be admirably helpful, will start saying things like; "your bearing clearances are too big", "you've got a failure in the making", "your filter sucks", and so on. These are always wild ass guesses because, just as in this case, the questioner doesn't give anywhere near enough information to make an informed evaluation. Doing it in person is demanding enough, doing it online is even more difficult/dangerous.

If appraiser had said that his pressure readings last week were 10# higher (for example) at EXACTLY the same rpm's, and temperatures, in EXACTLY the same operating conditions, with EXACTLY the same oil, filter, and gauge, I might be compelled to agree that he has a "problem". Therein lies the value of oil pressure readings as a diagnostic tool. But in this case we don't have the differential datum points, nor any historical knowledge of what the values were before as compared to now. All we have is the OPINION that they're too low to protect the engine. Thus you see appraiser doing what nearly everyone else does and that is GUESS at some solutions, just as respondents tend to GUESS at solutions. It's not unlike the owner who doesn't understand enough about how the engine operates and starts changing parts to "solve" a rough idle. He'll spend time and money putting on new wires, plugs, filters, dist caps, tweaking those "little screw things" on the carb and so on. In reality all he needed to do was replace the split vacuum line................a couple bucks, a couple minutes. I'm sure professional mechanics like Denny abhor the parts changing approach described here, so why is a similar approach to lubrication acceptable?

Appraiser may have a problem, but I'd be willing to bet if he follows the list of remedies he's posted, without making any real changes; e.g. higher viscosity oil, higher pressure or volume pump, nothing will change. Changing to a higher viscosity oil could well increase the reading on his gauge, but will it give him better lubrication. As a thought experiment let's say he has a 5w20 synthetic in there right now because the previous owner was told by someone he respected that synthetics are God's gift to lubrication (who knows? he didn't tell us anything about that). But now you guys (and probably others) have him spooked so he's going to really hit a home run (more is better!!:rolleyes: ) and put in some 20w50. Good guess is he'll see a real increase in his pressure gauge readins. The SAE (Society of Automotive Engineers...........but what do they know?) tells us that approximately 80% of normal wear in a typical passenger car engine occurs at start up because that is when the oil film that forms the hydrodynamic wedge of lubricant between opposing surfaces is at it's minimum. Though measured in miliseconds, a lighter (the 5w in this example) oil will get between the surfaces faster than the heavier (20w), thus affording "better" protection. NOTE: THIS EXAMPLE IS NOT INTENDED TO ENDORSE THE USE OF 5w20 OIL IN ALL, or any for that matter, ENGINE APPLICATIONS. It is merely an example to illustrate a point. Obviously the engine will need to be clearanced for an appropriate viscosity grade of oil. Again, we have no knowledge of what the specs on this engine are, so empirical examples are only guesses that may have no relevance to this specific engine.

My real point is that we do a disservice to anyone by fostering their fears (OH MY GOD, MY ENGINES FAILING.................ISN"T IT?), and/or causing them to unjustifiably pull their engine and overhaul just so they can, MAYBE, reach some artificial benchmark that we think is appropriate without benefit of knowing what is happening in reality.

As for adding "magic elixers", the best hope is they won't do any harm.

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Originally Posted by DennyW

Well Bob, by that post, we as a whole should not give any advice to anyone then. Don't say I missed it, because it all boils down to that statement. BRING YOUR CAR TO MY SHOP, AND I WILL CHECK IT OUT !! That should be all my answers from now on. :LOL: :LOL:

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You've been on here long enough that I would think you know that that is not anything like what I'm suggesting. What I am saying is that the "bring it in" is obviously impractical. What I am suggesting (and I realize it's likely a waste of time) is that we would be more helpful to those we seek to aid by asking questions that "force" them to look for the other factors that may be in play that we would do for ourselves if we did have the chance to physically examine the application. But we (the collective we) don't do that. Rather, in an effort to be what we perceive as helpful we start throwing out guesses that may or may not be appropriate before asking questions that both help us give a more accurate assessment and concurrently train, or further educate, the willing minded questioner.

Guys, It looks like there are a couple of different ways of looking at this.
Denny is taking the practical and the years of experience method and Bob is moving along the theoretical path. Both will get you to the same point eventually - there is something wrong with this engine and it needs fixing. I've been on both sides as a wrench turner and a service engineer trying to determine why a turbine power plant wont put out megawatts and turn the lights back on in town or a refinery.

While I do favor the engineering point of view for a multiple failure problem in a fleet, here we are only discussing a small block Ford engine, with unknown maintenance factors during its lifetime. There are several areas that can contribute, and I believe that we listed the most significant ones that can cause a problem in our experiences. Car appraiser is looking for some guidelines for a diagnosis for probable low oil pressure. We gave him some to consider now it's up to him on how he proceeds. Is the engine worn out? Maybe, but not until a few more dianostic steps can verify that there is significant problems and it needs to have at least some areas repaired or replaced.:HMMM:

Here is an update:
I changed the oil and filter using 10w-40 and a half a quart of Lukas oil stabilizer. At cold start, the preesure is about 50 psi. I think it was the oil filter since it was very heavy and looked old.

Once warm, the pressure is 25+ psi at 2500 rpm and 8-10 psi at idle. It runs well and for now, I'm going to leave it alone since I've got a lot of other changes I need to make like power brakes and revised differential ratio. The last owner put 255/70/R15's on the rear from a stock ford 8" automatic differential and the tires stick out from the fender 3", have only 2" clearance to the fender edge and make the car a dog off the line.

Thanks for the help.

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Originally Posted by Bob Parmenter

Denny, interesting non sequitur that only demonstrates that you didn't understand my point when I wrote that before, and you've not done any research, as I know you often do otherwise, to broaden your understanding of what I've said. And unlike most of the answers that are made in response to this frequently asked/stated question/comment I'm not answering in absolutes (other than stating that having oil present is more important than evaluating on an arbitrary number without context), so the remark about a 5-20# gauge is wholey inappropriate.

Ireland, your experience supports my statement even though most would think it's a challenge (perhaps you included) as the bottom of your range of experience at idle is within the range I posted, albeit the top. We can pick nits about precise numbers, but that misses the point as well. Lubrication isn't just about the numbers on a gauge, it's about the lubricant being at the point needing lubrication.

Would I like to see higher numbers than appraiser has listed? Sure, but only from the perspective of having a greater safety margin. He's operating at the bottom of the range that my experience and training shows to be adequate.

This thread, and nearly every other one that's dealt with oil pressure, so it's not unique, does a total disservice to proper diagnostic procedure. Usually folks, who's intentions are to be admirably helpful, will start saying things like; "your bearing clearances are too big", "you've got a failure in the making", "your filter sucks", and so on. These are always wild ass guesses because, just as in this case, the questioner doesn't give anywhere near enough information to make an informed evaluation. Doing it in person is demanding enough, doing it online is even more difficult/dangerous.

If appraiser had said that his pressure readings last week were 10# higher (for example) at EXACTLY the same rpm's, and temperatures, in EXACTLY the same operating conditions, with EXACTLY the same oil, filter, and gauge, I might be compelled to agree that he has a "problem". Therein lies the value of oil pressure readings as a diagnostic tool. But in this case we don't have the differential datum points, nor any historical knowledge of what the values were before as compared to now. All we have is the OPINION that they're too low to protect the engine. Thus you see appraiser doing what nearly everyone else does and that is GUESS at some solutions, just as respondents tend to GUESS at solutions. It's not unlike the owner who doesn't understand enough about how the engine operates and starts changing parts to "solve" a rough idle. He'll spend time and money putting on new wires, plugs, filters, dist caps, tweaking those "little screw things" on the carb and so on. In reality all he needed to do was replace the split vacuum line................a couple bucks, a couple minutes. I'm sure professional mechanics like Denny abhor the parts changing approach described here, so why is a similar approach to lubrication acceptable?

Appraiser may have a problem, but I'd be willing to bet if he follows the list of remedies he's posted, without making any real changes; e.g. higher viscosity oil, higher pressure or volume pump, nothing will change. Changing to a higher viscosity oil could well increase the reading on his gauge, but will it give him better lubrication. As a thought experiment let's say he has a 5w20 synthetic in there right now because the previous owner was told by someone he respected that synthetics are God's gift to lubrication (who knows? he didn't tell us anything about that). But now you guys (and probably others) have him spooked so he's going to really hit a home run (more is better!!:rolleyes: ) and put in some 20w50. Good guess is he'll see a real increase in his pressure gauge readins. The SAE (Society of Automotive Engineers...........but what do they know?) tells us that approximately 80% of normal wear in a typical passenger car engine occurs at start up because that is when the oil film that forms the hydrodynamic wedge of lubricant between opposing surfaces is at it's minimum. Though measured in miliseconds, a lighter (the 5w in this example) oil will get between the surfaces faster than the heavier (20w), thus affording "better" protection. NOTE: THIS EXAMPLE IS NOT INTENDED TO ENDORSE THE USE OF 5w20 OIL IN ALL, or any for that matter, ENGINE APPLICATIONS. It is merely an example to illustrate a point. Obviously the engine will need to be clearanced for an appropriate viscosity grade of oil. Again, we have no knowledge of what the specs on this engine are, so empirical examples are only guesses that may have no relevance to this specific engine.

My real point is that we do a disservice to anyone by fostering their fears (OH MY GOD, MY ENGINES FAILING.................ISN"T IT?), and/or causing them to unjustifiably pull their engine and overhaul just so they can, MAYBE, reach some artificial benchmark that we think is appropriate without benefit of knowing what is happening in reality.

As for adding "magic elixers", the best hope is they won't do any harm.

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Very interesting theory about "Obviously the engine will need to be clearanced for an appropriate viscosity grade of oil."
This is far from true.
An engine is clearanced depending on it's usage and application.
If I used your theory I would end up with a lot of spun main and rod bearings.

If you're picking nits, then yes, it would have been more accurate to state it the other way around. The viscosity needed would, in part, depend on the clearances chosen (excluding any other ambiant conditions). Oh, btw, that's not theory, it's practical application.