Small Block Oil Pump/Pressure help needed

[Dave S.]

I have a 65 L84 car that runs as it should but the Oil pressure is way to high (65-70 lbs at hot idle). Obviously to high for proper operation and certainally to high for a PV. I have the oil pump out and it is a GM pump which was installed on the motor when it was rebuilt in the mid 80's. Main casting is GM2796 and the lower casting is GM176 with 4180 below it. Looking for advice as to wether I should try to change the spring on my existing pump or just install a new stock pressure pump. The spring is held in by a small drive pin which look like it may be difficult to remove. Seems Melling 55 would be the proper choice for a replacement.
Any guidance is appreciated.

[Page C.]

Re: Small Block Oil Pump/Pressure help needed

Hi Dave,
The high pressure spring is GM# 3848911. It's still available from GM parts. Cost was about $7.50. It's also easy to remove the pin to change the spring. I used a drop of red Locktight on the pin when I reinstalled it into the pump housing. My new spring also had white marking paint on a few of the coils.
Page

[Dave S.]

Re: Small Block Oil Pump/Pressure help needed

Hi Dave,
The high pressure spring is GM# 3848911. It's still available from GM parts. Cost was about $7.50. It's also easy to remove the pin to change the spring. I used a drop of red Locktight on the pin when I reinstalled it into the pump housing. My new spring also had white marking paint on a few of the coils.
Page

Page,
I need to lower the Oil Pressure. Is there an OEM standard pressure spring.?
Looking to get 30-35 psi at hot idle.

[Edward J.]

Re: Small Block Oil Pump/Pressure help needed

Dave,
I know its a little late now, but did you happen to check the pump pressure with a external gage? It may be possible that the gage may not be accurate?? and the other possibility that the original spring was changed out during the rebuild. like Page said the springs are sometimes color coded. Joe L. see the post and give you the low down on the springs for pump pressure changes, I would say stay with the original pump as the rarely wear out and change the spring, it sounds like the pump is working well, and replace the drive shaft plastic coupling while your there.

[Joe L.]

Re: Small Block Oil Pump/Pressure help needed

Page,
I need to lower the Oil Pressure. Is there an OEM standard pressure spring.?
Looking to get 30-35 psi at hot idle.

Dave------


There are only 2 springs. The standard pressure spring is GM #3814903; the high pressure spring is GM #3848911, Both remain available from GM.

Your application originally used a pump with the high pressure spring installed although the pressure you report does seem somewhat higher than I would expect. It could be that some aftermarket spring was installed. There's no way to tell which GM spring was originally installed in the pump you have by reference to the casting numbers on the pump as both standard and high pressure pumps differed only by the installed spring.

The first thing that I would suggest doing is to install an accurate test gauge to determine if the dash gauge readings you're getting are accurate.

[Ralph E.]

Re: Small Block Oil Pump/Pressure help needed

Dave, back in 2002 I had the same problem, HIGH OIL PRESSURE. I talked with Melling and they sent me a new oil pump, issue corrected.

[Dave S.]

Re: Small Block Oil Pump/Pressure help needed

Dave,
I know its a little late now, but did you happen to check the pump pressure with a external gage? It may be possible that the gage may not be accurate?? and the other possibility that the original spring was changed out during the rebuild. like Page said the springs are sometimes color coded. Joe L. see the post and give you the low down on the springs for pump pressure changes, I would say stay with the original pump as the rarely wear out and change the spring, it sounds like the pump is working well, and replace the drive shaft plastic coupling while your there.

It seems at this point I should install a 911 spring and see then what I have. At least I'll have the proper pump installed. If the readings are still to high then my gauge is likely the culprit.

[Edward J.]

Re: Small Block Oil Pump/Pressure help needed

Dave, What does the 65 service manual say about the normal pressures?? I am pretty sure the normal start-up pressure is around 55-60 and warm around 45-50?? 30-35 seems on the low side.

[Edward J.]

Re: Small Block Oil Pump/Pressure help needed

Another note Dave, no two cars were ever the same with pressure, engine bearing fit and oil pumps out put determine the pump pressures, some engines were built with tighter tolerances which creates higher pressures( a good thing). there I a good read in the simular thread below I just read.

[Kenneth T.]

Re: Small Block Oil Pump/Pressure help needed

If you get a melling pump you still have to change the spring to a green one which are sold separately

this will make your oil pressure to stock specifications

[Duke W.]

Re: Small Block Oil Pump/Pressure help needed

The AMA specs have oil pressure specs for the various engines.

Oil pressure is specified for a fully warmed up engine - engine oil at normal operating temperature, which takes a while after coolant is up to the normal range, at 2000 RPM.

THERE IS NO SPECIFIED OIL PRESSURE AT IDLE SPEED, and it's highly dependent on idle speed, so SHP engines even with the "standard" oil pressure spring will typically have higher pressure idling in the 750-900 range than a base engine at 500.

The standard spring should yield pressure in the range of 40-45 @ 2000(hot), and the "high pressure" spring used on very late '63 and subsequent mechanical lifter small blocks is 55-60 @ 2000 (hot), and all production small blocks used the "standard volume" pump, which is perfectly adequate short of all out racing.

Applications that originally had the standard pressure spring should have a 60 psi gage, and original high pressure applications an 80 psi gage.

The aftermarket, Melling in particular, does not appear to offer proper OE replacement springs. Most allow too high pressure for standard pressure applications. The do sell a "spring kit" that has been discussed here, but you're probably better of biting the bullet, paying the GM price for the correct spring for your application that Joe listed above.

Many serviceable oil pumps get replaced, apriori. However, unless they have ingested debris over their life, they are usually quite serviceable, and are simple to disassemble and inspect.

I've lost count of how many "high oil pressure" threads have been started over the year because some "engine builder" installed a high volume, high pressure pump or a standard volume pump with a too high pressure relief spring.

Duke

[Dave S.]

Re: Small Block Oil Pump/Pressure help needed

The AMA specs have oil pressure specs for the various engines.

Oil pressure is specified for a fully warmed up engine - engine oil at normal operating temperature, which takes a while after coolant is up to the normal range, at 2000 RPM.

THERE IS NO SPECIFIED OIL PRESSURE AT IDLE SPEED, and it's highly dependent on idle speed, so SHP engines even with the "standard" oil pressure spring will typically have higher pressure idling in the 750-900 range than a base engine at 500.

The standard spring should yield pressure in the range of 40-45 @ 2000(hot), and the "high pressure" spring used on very late '63 and subsequent mechanical lifter small blocks is 55-60 @ 2000 (hot), and all production small blocks used the "standard volume" pump, which is perfectly adequate short of all out racing.

Applications that originally had the standard pressure spring should have a 60 psi gage, and original high pressure applications an 80 psi gage.

The aftermarket, Melling in particular, does not appear to offer proper OE replacement springs. Most allow too high pressure for standard pressure applications. The do sell a "spring kit" that has been discussed here, but you're probably better of biting the bullet, paying the GM price for the correct spring for your application that Joe listed above.

Many serviceable oil pumps get replaced, apriori. However, unless they have ingested debris over their life, they are usually quite serviceable, and are simple to disassemble and inspect.

I've lost count of how many "high oil pressure" threads have been started over the year because some "engine builder" installed a high volume, high pressure pump or a standard volume pump with a too high pressure relief spring.

Duke

Thanks to all for the great input. Seems in my case I should have checked the gauge first but seeing as the pump is out of the car I'll install the GM "high pressure" spring and see how it performs. If the oil pressure remains to high it is likely I have a bad gauge.

[Gary B.]

Re: Small Block Oil Pump/Pressure help needed

Dave,
The standard oil pressure spring, for hydraulic lifters, is Melling 55049, they come in a package of 5 springs. I you need a "green" low pressure spring, let me know, I'll mail one to you. The yellow, 55048, what I call a medium pressure spring, most solid lifter engines use these. That is what all Melling pumps are shipped with today. Melling also offers a high-pressure spring, 55070, which is pink. All the oil pump spring rates can be found on the Melling web site:

http://www.melling.com/Portals/0/Spring%20Packs%20Updated%20PDF%20100710.pdf?ver=2010-10-07-082542-910

Gary B

[Gary R.]

Re: Small Block Oil Pump/Pressure help needed

I had a similar issue back a couple of years with the rebuilt 350 in my 72. I did the build and used a new M55 pump but my gauge was always pegged when cold. I looked at the springs and was planning on pulling the pump but I first did the easy thing- I changed from 15w40 oil back to 10w-40 that I always used and that was all I needed to do. Normal function with the first start up.

[Loren L.]

Re: Small Block Oil Pump/Pressure help needed

For your benefit and the Performance Verification nit-pickers, please let me refer you to page 6 of the July 1965 Chevrolet Service News:

"High Engine Oil Pressure!
Corvette 327 CU. In. - 365-375 HP.

The above 327 cu. in. high performance Corvette
engine oil pressures in the area of 80-95 psi (at
2,000 RPM) can be expected and are perfectly
normal. However, damage may occur to this en-
gine if the 283 cu. in. engine oil pump is used
which delivers oil pressure of 65 psi at 2,000 RPM."