Oil Pressure
Thread Starter
Instructor
Joined: Sep 2013
Posts: 118
Likes: 1
Oil Pressure
I have a 1971 C-3 w/small block 350 motor. Oil pressure stays @ 70 PSI. Is that normal or do I need to investigate why it is reading so high? I recently purchased the car & was told the motor was rebuilt 7-8 months ago. It does seem to be using a little oil. Do I need to be concerned?
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Check your gauge to see if it's reasonably accurate. When the engine was rebuilt, they most likely installed a high volume/pressure pump if the gauge is close. Myself, I don't have a real problem with oil pressure like yours, but the rule of thumb 10psi/1000 RPM is not all bad. The downside to that high of pressure is the lower busing in the distributor takes a beating, not to mention the extra load on the cam and timing chain.
Using a little oil? How much is a little? Leaks? Exhaust smoke?
Using a little oil? How much is a little? Leaks? Exhaust smoke?
Melting Slicks
Joined: Nov 2010
Posts: 3,363
Likes: 32
From: Bowtie, Pennsyltucky
St. Jude Donor '13-'14-'15,'21
My stock, low-mile '71 350 has 30-35 psi @ idle at operating temp.
I can see why there would be added wear on the cam and dist. bushing as mentioned above, as when I was priming the engine after sitting for 25+ years with a 1/2" drill, I was surprised how much power it took to run the stock pump. That drill got hot!
I can see why there would be added wear on the cam and dist. bushing as mentioned above, as when I was priming the engine after sitting for 25+ years with a 1/2" drill, I was surprised how much power it took to run the stock pump. That drill got hot!
Le Mans Master
Joined: Feb 1999
Posts: 8,351
Likes: 75
From: Tampa Bay FL
I recently replaced the high volume pump with a stock volume pump. It maybe dropped 10psi across the board.
When cold, it pegs at 70-80psi just like the high volume pump. Only difference I see is when it is warmed up, it drops to about 30psi at idle and would rarely drop below 40psi at idle with HV unit.
Overall, I didn't see a lot of difference. I still get 60psi at speed fully warmed up with stock unit. It is a Mellings M55 unit. The HV was an M55HV.
Only reason I swapped was warnings about using HV with my retro roller; Comp said to use stock volume oil pump. I think it has to do with not overwhelming the oil filter bypass and so the oil is getting filtered.
When cold, it pegs at 70-80psi just like the high volume pump. Only difference I see is when it is warmed up, it drops to about 30psi at idle and would rarely drop below 40psi at idle with HV unit.
Overall, I didn't see a lot of difference. I still get 60psi at speed fully warmed up with stock unit. It is a Mellings M55 unit. The HV was an M55HV.
Only reason I swapped was warnings about using HV with my retro roller; Comp said to use stock volume oil pump. I think it has to do with not overwhelming the oil filter bypass and so the oil is getting filtered.
Le Mans Master
Joined: Feb 1999
Posts: 8,351
Likes: 75
From: Tampa Bay FL
I have a 1971 C-3 w/small block 350 motor. Oil pressure stays @ 70 PSI. Is that normal or do I need to investigate why it is reading so high? I recently purchased the car & was told the motor was rebuilt 7-8 months ago. It does seem to be using a little oil. Do I need to be concerned?
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Melling High Performance pumps typically come with both a high- and low-pressure spring for the bypass built into the pump.
HV pumps create artificially high pressure, forcing the pump into bypass, by forcing too much oil through tight bearing clearances. Even without a high-volume pump, as long as the high-pressure spring is still in place, the oil pump will likely still put out relatively high pressures. If oil needs to be restricted to the heads, there are other means such as oil restrictor plugs.
http://www.melling.com/Aftermarket/High-Performance
HV pumps create artificially high pressure, forcing the pump into bypass, by forcing too much oil through tight bearing clearances. Even without a high-volume pump, as long as the high-pressure spring is still in place, the oil pump will likely still put out relatively high pressures. If oil needs to be restricted to the heads, there are other means such as oil restrictor plugs.
http://www.melling.com/Aftermarket/High-Performance
Race Director
Joined: Oct 2005
Posts: 12,470
Likes: 1,548
From: Camp Verde AZ
C1 of Year Finalist (performance mods) 2019
2017 C1 of Year Finalist
There is a difference between high volume, and high pressure.
You can have a normal volume pump, with a high pressure bypass spring, like was used in the early Z28 motors #3848907.
High volume pumps have taller and or wider pump gears, and may, or may not be high pressure. pressure is determined by the bypass spring, regardless of volume.
I have used the Z28 pump for years, in two different motors (same pump), it runs 60-65 at speed, and perhaps 25 at idle. The normal pump would run perhaps 45 PSIG at speed, and have the same idle pressure
Doug
You can have a normal volume pump, with a high pressure bypass spring, like was used in the early Z28 motors #3848907.
High volume pumps have taller and or wider pump gears, and may, or may not be high pressure. pressure is determined by the bypass spring, regardless of volume.
I have used the Z28 pump for years, in two different motors (same pump), it runs 60-65 at speed, and perhaps 25 at idle. The normal pump would run perhaps 45 PSIG at speed, and have the same idle pressure
Doug
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Le Mans Master
Joined: Nov 2006
Posts: 7,215
Likes: 1
From: Orlando FL
Step one= Is the oil pressure really this high? Is the meter or sending unit dodo?
Step two= Fix the indication problem and
or evaluate why the pressure is so high even when the engine is hot
Step three= address the high pressure issue and then
Step two= Fix the indication problem and
or evaluate why the pressure is so high even when the engine is hot
Step three= address the high pressure issue and then