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Need some help - loosing oil pressure at high rpm's
Hey guys I am no engine expert but am pretty good. 351 stroked to 427. By the gauge on the dash my oil pressure is 35 -52 psig from idle to 4K. Once it hits 4K oil pressure drops rapidly to 45 psig and stays there through 6K.
Here the kicker I checked oil pressure before the oil cooler and it pegged at 65-69 psig all the way to 6k rpm's. no drop what so ever. is the oil cooler or oil pump the problem. Additional details: Mellon high volume oil pump 8 quart pan - I dropped and calibrated dip stick originally of 1.5 quarts! Superformance Cobra with recently replaced oil cooler by previous owner**) why I don't know as he is NOT A CAR GUY nor are his mechanics:LOL: I checked rod and main caps they were immaculate as was the rest of the internals of the engine. zero particles in the pan. I couldn't believe how great it looks inside there. cam, dist gear all perfet. Checked compression and all were 195 -200. I took apart the oil pump it looked perfect I did crank in on the rv screw a little which appeared it did help. as before it was dropping from 50-40 psig. how do I work around this problem? when cold the oil pressure was 70 psig and the rv lifted. is there a limit on the oil pump pressure I want to avoid? Thanks!!!!!! |
Cap the lines to the cooler to drop it out of the system. That will identify if the cooler's restricted or tell you if the problem's in the block.
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Just need to figure out how to bypass. It has a remote filter mount as there is not enough room to put filter directly on block
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You should be able to bypass the cooler by buying a male to male union and hook the cooler lines together. One line should be from the filter to the cooler and the other goes back to the engine.
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After capping the lines, if there is no change, it could unfortunately be an indication of loose bearings.
ALSO: You might have a crack in the oil pickup tube, or depending on static volume of pan, you could be pulling oil out of the pan faster than it can drain back in to keep the pickup submerged and prevent a vortex. |
Thanks. As far ad loose bearings the two I checked looked great, not that it guarantees they all do. I have a 4 post lift so pretty easy to access and change bearings.
Thanks for the union idea!!,!!! |
Excellent points! My first thought. That is why I dropped th pan and determined the dipstick was off 1.5 quarts at full. I checked pickup to pan and it was 1/2 inch. Pickup pipe was good however I did find where one of the button head screws on one of the baffle support was rubbing the line and would eventually run a hole.
Po called and said original cooler had a leak. This one was installed a month ago. A long time I talked with Mellon and they said the hv pump volume reaches maximum at 4 k rpms and really taper off. Funny that is where I notice the quick drop and stabilization. Quote:
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Your cooler and lines aren't big enough.
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If it was bearings causing a drop in the engine, you should also see a drop in pressure at the cooler inlet. This tends to say there is a restriction somewhere after the cooler inlet. Perhaps a tear inside a line has a flap folding over at higher flow rates. Get a good gauge that doesn't peg out. Have the engine completely warmed up, so temp/viscosity changes don't fool you. Use that gauge everywhere you check, so you are comparing apples to apples. See what the pressure is before the cooler, at the cooler exit, and at the other end of the return line to the engine. It there are any other connections check each side of it as well. Use a scientific approach to track down the problem, and resist the temptation to jump to assumptions. |
Max its the resistance in the cooler and or the lines. I have had the same issue before (Remember u disagreed with me :D).
The fix = make a more efficient oil circuit, or change the spring in the pump. I have always ended up changing the spring. Mark |
Thanks. I used the same calibrated gauge before the oil cooler and at the block tap. A real pia to unscrew and rescrew the fitting on the block. I foun oltoff offers a larger oil cooler. It may be the cheapest route vs a bypass or thermostat. Having a hard time figuring a simple solution to bypassing the cooler. Will the limes have enough slack to pull together so I can use a union to test.
The pressure drop is so repeatable it would seam a hose flap wold be a little eratic. I will call the sho who installed the cooler fo 1500 (wtf) and determine whose it is as I cannot find any part numbers or other identifiers. |
Max,
If you need a piece of hose to join the two together, let me know how long a piece you need. I have some under the bench, but I don't have any fittings left. |
I use a HV H/P Melling pump on my 289, the later improved design with the shaft through the base plate (much improved). The volume for the 289/302 HV pump is the same as Std Volume for 351. That being said I use a size 10 Hose, a Sertab 21 row cooler about 4" tall and filter about 5' tall mounted on frame rail (due to physical room). It carries 70 lbs while at speed and about 30 lbs at idle. The shortblock has been together 20 years with the same bearings throughout. The HP pumps bypass at about 70-75 lbs as they come out of the box. I fit this pump when it became available instead of the original HV pump with a shimed spring. Try to keep the pump pickup 3/8" from and parallel to the pan floor. A HV pump will require a larger capacity (than std) pan. The difference between your application and mine would be the bearing sizes if you are running 351W, otherwise 289/302 are identical. My engine is Solid lifter flat tappet. With performance bearing clearances.
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Interesting i have alot of thinking to do it should pump the volume!!!! What do you mean by changing out the spring. The one in the oil pump. It has an adjustment and I did turn it in about 3/4 of a turn. I could have gone a lot further. To be honest I don't know how much it was engaged until I turned it in. So if the pump Rv is theoretically reset to 80psig will that solve the issue? Is it possible the pressure drop across the cooler will just grow with higher pressure/flow and never supply the engine.
As far as plumbing standard superformamce an 10 hoses and fittings identicle to my last one. My last one had a 7 psig drop across the cooler(stock SPF) I have a lot of data from my oil filter experiment a couple years back. By the way on this one I use 3.99 ford fl1a from walmart with Mobil 1 10w40 high mileage ( extre zinc/phosphorous.) Quote:
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The plot thickens!!! The new oil cooler a Mocal A13A10 is the correct and identicle replacement for a Superformance. Beleive it or not it only holds .20Qt!!!!!!!!!!!!!!!!! I spoke with Olthoff and they said crank in on the oil pump spring or go to 12 AN. I have no desire to go to 12 AN fittings. To much work and cost.
I spoke with Mello. The M83HV flows 4 gpm at 2000 rpm, 8 gpm at 4000 rpm and 8 gpm at 6000 rpm so as you can see above 4k rpm it does level out. Max pump pressure is 85 psig. Now I question if it is a bearing issue. The question now is it easier to drop the pan and crank in on the rv screw or make a by-pass for the oil cooler. I would love to bypass the cooler but i am so inpatient i will not wait for the fittings and line. go figure who knows!!!!!! |
take the hose off the cooler and reroute it to the block-no parts needed----
a possibility is that the cooler is cooling the oil to the point that it thickens and won't flow anymore so you might try blocking the airflow to it and not running at high rpm until oil is over 200* It could also be that the way you have your pressure guage plumbed that you have a venture effect past it causing a psi drop at that rpm AND-----you could have all the oil pumped outta the pan by that rpm with the HIGH volume pump and it just hasn't returned to the sump-------- |
If you need the cooler, replace the lines with -12AN. If you don't need it, bypass it and run -12AN lines to and from the remote oil filter. It's the size of the lines that are reducing your oil pressure.
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please remember i am getting 65 psig before the cooler consistently. this would validate the pan is not getting sucked dry, the pick up tube is good, the oil pump is working. I may be able to reuse one of the oil pump remote cooler lines to temporary plum back to filter adapter. great idea.
does anyone know of a super short oil filter with the same dimension of the motorcraft fl-1a? if so I could unscrew the filter adapter (what the lines plug into) and just screw a filter on the block for testing. That would defenitley eliminate the whole oil cooler remote lines etc. |
Please remember all spf are plumbed with 10an lines as well as my last one without this issue. the oil cooler is 95% of the restriction that being said it was not an issue with my last one.
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I guess I am not concerned with the reduction in oil pressure as much as the sudden drop above 4k rpm. in other words if I just had low oil pressure I would crank in on the oil pump rv adjustment. It is the sudden drop from 50 to 42 psig that has me stumped above 4 k rpm. so it drops from 4K to 4.3K than holds seady at 42 until 6k rpm's.
I imagine I could passify the issue with cranking in on the oil pump rv setting. but i wonder if i would still see the step change in oil pressure. |
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