oil pressure question
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oil pressure question
I just installed a mechanical oil pressure gauge in my 239 flathead last night. It shows that when I start it up after the engine has cooled it idles at about 25-30 psi and 40-45 when I'm driving down the road but as soon as the motor get up to temp it drops to 20 while I'm driving and 0-2 when it's idling. I'm using valvoline 10w40. Is the oil getting too thin when warm? Do I need to go to a heavier oil? I'm wondering too if this could have anything to do with the oil screen. Would it allow sludge to clog it up as the oil pump is pulling the oil out of the pan and settle back on the bottom if it sits for long enough? Any help would be greatly appriciated.
Lead Driver
Joined: Apr 2002
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From: Littleton, New Hampshire
I'd think you would want a minimum of about 10 pounds idling and hot. It might help some to use straight 30 or 40 weight oil instead of multiple viscosity but I would not count on that either. If this is a high mileage engine you may have too much main bearing clearance.... 
Fleet Owner
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From: NM
I wonder if your oil filter can has the correct fitting in it? It is supposed to have a restrictor. If it isn't something like that, I think you need a new pump or bearings. I'd pull the pan, it's pretty easy and you'll get a lot of answers.
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Hi,
I had the same problem, albeit with my 1976 302. Everyone thought it was probably the sieve. So my truck was going to have it's sump off and checked.
However, the garage firstly flushed the engine and got some crud out. Since then it's been fine. I don't think they could be bothered trying to get the engine out, so it all ended quite well.
Someone else told me they'd poured in some parafin (kerosene?) and idled, then flushed and new oil which seemed to do the trick.
Best of luck,
QbE
I had the same problem, albeit with my 1976 302. Everyone thought it was probably the sieve. So my truck was going to have it's sump off and checked.
However, the garage firstly flushed the engine and got some crud out. Since then it's been fine. I don't think they could be bothered trying to get the engine out, so it all ended quite well.
Someone else told me they'd poured in some parafin (kerosene?) and idled, then flushed and new oil which seemed to do the trick.
Best of luck,
QbE
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I'd think you would want a minimum of about 10 pounds idling and hot. It might help some to use straight 30 or 40 weight oil instead of multiple viscosity but I would not count on that either. If this is a high mileage engine you may have too much main bearing clearance....
What does the resrictor look like and where would it be located? I can take a look at it tonight and see.
Hotshot
Joined: Nov 2000
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From: Pflugerville, tx
we had the same problem on my daughters 2002 Ford Focus, low pressure engine warm.. turned out they used a filter WITH restrictor, but should not have. changing the filter solved that one problem.
(of course I changed the oil pressure sensor first, assuming they could read the right part number... wrong assumption, one line off)
Sam
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From: Riverside, So Cal
I agree with Vern (GreatNorthWoods) about a higher viscosity oil. It will allow you to better diagnose the problem. If the heavier oil helps, the bearings are worn. A high mileage motor oil would do the same type of thing, perhaps a little better, since the whole idea here is that the thicker oil better fills the larger bearing clearance.
No, generally the mains cannot be changed easily with the motor still in the truck. The rod bearings can, but not the mains.
BTW, maintaining correct oil pressure depends ENTIRELY on a close clearance between the MAIN bearings and their journals AND a slightly larger clearance between ROD journals and their bearings. Oil flows FROM the mains TO the rods. If the clearances are not stepped correctly, one of the two journals will starve for oil and the bearing will burn, destroying the engine. Don't change one set of bearings without changing the other.
If going to a higher viscosity helps, you will have put off the needed overhaul for awhile.
Also, I noticed from your profile that you live in ND. Driving (starting) this truck daily in the winter will be a big problem with higher viscosity oil unless you have an engine block heater while it is in the garage. But you probably already know that.
No, generally the mains cannot be changed easily with the motor still in the truck. The rod bearings can, but not the mains.
BTW, maintaining correct oil pressure depends ENTIRELY on a close clearance between the MAIN bearings and their journals AND a slightly larger clearance between ROD journals and their bearings. Oil flows FROM the mains TO the rods. If the clearances are not stepped correctly, one of the two journals will starve for oil and the bearing will burn, destroying the engine. Don't change one set of bearings without changing the other.
If going to a higher viscosity helps, you will have put off the needed overhaul for awhile.
Also, I noticed from your profile that you live in ND. Driving (starting) this truck daily in the winter will be a big problem with higher viscosity oil unless you have an engine block heater while it is in the garage. But you probably already know that.
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if you take off the filter, where it screws on to the engine, can you see all the way inside the filter? If so, no restrictor. Basically a flow control valve.
we had the same problem on my daughters 2002 Ford Focus, low pressure engine warm.. turned out they used a filter WITH restrictor, but should not have. changing the filter solved that one problem.
(of course I changed the oil pressure sensor first, assuming they could read the right part number... wrong assumption, one line off)
Sam
we had the same problem on my daughters 2002 Ford Focus, low pressure engine warm.. turned out they used a filter WITH restrictor, but should not have. changing the filter solved that one problem.
(of course I changed the oil pressure sensor first, assuming they could read the right part number... wrong assumption, one line off)
Sam
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Okay. I get you now. I have the canister setup. I'm going to put a heavier oil in it tonight and see where that gets me. If I pull the oil pan off, what do I need to look for that would be an indication of worn mains, ect.?
Fleet Owner
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From: NM
Flatheads are totally different than OHV engines. The restrictor is at the tubing connection to the Tee at the filter; pull off the line from the block, remove the pressure sender (if you still have one), and remove the Tee from the filter housing. Hold the Tee up to the light and look through the filter end of it. The opening should only be about .060" as I recall.
You can impriove oil pressure by eliminating the filter completely, they were an option. It may be good for up to 5 psi across the board.
RJ's comments on bearings are good, but flatties frequently lose pressure when the cam bearings wear. You know that's not good news! Another possibility is that the pump's relief valve is sticking. Again, I'd pull the pan and check the screen and pickup first, the pump second, then go into the bearings if you don't see any problems with the supply side. You can plastigage the bearings with the crank in.
You can impriove oil pressure by eliminating the filter completely, they were an option. It may be good for up to 5 psi across the board.
RJ's comments on bearings are good, but flatties frequently lose pressure when the cam bearings wear. You know that's not good news! Another possibility is that the pump's relief valve is sticking. Again, I'd pull the pan and check the screen and pickup first, the pump second, then go into the bearings if you don't see any problems with the supply side. You can plastigage the bearings with the crank in.
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From: Riverside, So Cal
While there, pull a rod bearing as well and check it the same way. Rods usually wear faster than mains. DO NOT MIX UP THE BEARING CAPS! They need to go back where and how they were.
There is an old school product called "Plastigage" that is used to determine bearing clearance. It is available at most auto parts stores. Napa is my favorite place to ask for products like this. Plastigage is wax string of a very closely held diameter. You break off a small length, lay it on the clean crank journal, reapply the bearing cap and torque it down. The take it apart and measure the squished width of the wax string with the edge of the package and read your bearing clearance.
Check with the Napa guy as to what your motor bearing clearances should read. Hw should have a book to look it up in.