# Oil pressure high on a rebuilt engine.



## Dukes67 (Jun 19, 2018)

So I had an extra 67’ 400 engine sitting around and decided to rebuild it. After the initial start the oil pressure came right up to 60psi. Immediately after starting the engine I brought it up to 2000-2500 to break in the cam. While running during the 30 min break in period the oil pressure was pretty much right on 60psi the entire time. All other indications from the engine seemed normal. After the break in period I brought the engine down to idle and the oil pressure at 850 rpm dropped to about 30psi.. Is the 60 psi at 2500 a concern that should be looked into? My GTO seems to run quite a bit lower at those rpm’s (35-40 psi). After the break in I checked the oil (Driven break in oil) and it looked clean. I also cut the filter open and inspected it and it looked good. Compressions were also checked and were all 150psi +\- 2 psi on all 8 cylinders. During assembly I checked the clearance on the rotating assembly and they were all within in spec. It’s a new Scat forged 461 crank with their supplied bearings. Oil pressure is being taken off of the oil filter housing. If this is a problem is there a way to lower the oil pressure via a spring like other engines I’ve worked on?


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## Old Man Taylor (May 9, 2011)

None of those pressures are a concern.


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## 1968gto421 (Mar 28, 2014)

Your rebuilt engine has normal oil pressure for a Pontiac engine. It's the engine in your GTO i'd be concerned with as 35-40 psi is actually pretty low. My 428 has oil pressure like that and 10-15 psi at idle. Mine either needs a rebuild (most likely) or has Pontiac's 40psi oil pump which was used in econo engines. Being a 428 (not econo), I suspect a rebuild is in my future. Your rebuilt 461 sounds in great condition, don't worry about it.


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## Mine'sa66 (Oct 30, 2019)

Dukes67 said:


> So I had an extra 67’ 400 engine sitting around and decided to rebuild it. After the initial start the oil pressure came right up to 60psi. Immediately after starting the engine I brought it up to 2000-2500 to break in the cam. While running during the 30 min break in period the oil pressure was pretty much right on 60psi the entire time. All other indications from the engine seemed normal. After the break in period I brought the engine down to idle and the oil pressure at 850 rpm dropped to about 30psi.. Is the 60 psi at 2500 a concern that should be looked into? My GTO seems to run quite a bit lower at those rpm’s (35-40 psi). After the break in I checked the oil (Driven break in oil) and it looked clean. I also cut the filter open and inspected it and it looked good. Compressions were also checked and were all 150psi +\- 2 psi on all 8 cylinders. During assembly I checked the clearance on the rotating assembly and they were all within in spec. It’s a new Scat forged 461 crank with their supplied bearings. Oil pressure is being taken off of the oil filter housing. If this is a problem is there a way to lower the oil pressure via a spring like other engines I’ve worked on?


Nope, perfect.


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## Dukes67 (Jun 19, 2018)

Thanks for the responses you guys. The other engine was rebuilt by a machine shop in town and I can’t say that I’ve been the happiest with the way it seems to run. Maybe it’s time to swap them out?


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## PontiacJim (Dec 29, 2012)

Dukes67 said:


> Thanks for the responses you guys. The other engine was rebuilt by a machine shop in town and I can’t say that I’ve been the happiest with the way it seems to run. Maybe it’s time to swap them out?


Pontiac offered 2 different oil pumps, one having 40 PSI on the non-high performance cars and the 60 PSI pump for high performance engines like the GTO or HO 428. So the previous engine may have had a 40 PSI pump installed by someone, or bearings are excessively worn. The weight of the oil used can also have a slight affect on oil pressure. 

Pontiac rates the oil pressure at 2,600 RPM. With a new engine, the clearances are tight and may drop a little over time. General rule is 10 PSI of oil pressure for each 1,000 RPM. So your pressures look good.


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## Dukes67 (Jun 19, 2018)

Thanks for the reply Jim. I put the 60 psi pump in and it’s right at 60 psi. At idle it’s about 30. All the other indication were good and the oil looked clean. I put the center springs back in the valves and I’m getting ready to run it for another 15-30 mins. Hopefully keeps running good!


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## maw2078826 (May 1, 2020)

PontiacJim said:


> Pontiac offered 2 different oil pumps, one having 40 PSI on the non-high performance cars and the 60 PSI pump for high performance engines like the GTO or HO 428. So the previous engine may have had a 40 PSI pump installed by someone, or bearings are excessively worn. The weight of the oil used can also have a slight affect on oil pressure.
> 
> Pontiac rates the oil pressure at 2,600 RPM. With a new engine, the clearances are tight and may drop a little over time. General rule is 10 PSI of oil pressure for each 1,000 RPM. So your pressures look good.


Pontiac made one more oil pump that you may remember, under Gr. 1.652, part number: 480246, (1973-74 455 SD) it had a 90 pound pressure relief spring...I made the mistake of putting it in a 455 I built and it pumped way too much oil into the heads...dropped it out and replaced it with a 60 pound pump. Dukes67 Oil pressure looks good.


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## Thered72 (Jul 30, 2020)

I have a newly rebuilt 400 in mine and I’m running the same exact pressure at idle and cruising. I drove it all summer and gave it WOT a bunch of times with no issues. Like they said.....probably normal. I was worried too lol


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## Droach6498 (Nov 1, 2020)

None of those pressures are a concern.
[/QUOTE]
I have a freshly rebuilt 67400 bored to .070 eagle crank 4.25 lift aluminum heads Lunati cam 270/278 dur pistons are low compression so I can run 94 octane I put in some 91 it runs fine, so nothing radical but the oil pressure is 90 at idle and 90-100 o.p. running this is with a elec sensor at the filter Im thinking of getting a mech sensor the engine has about 50 miles on it is this a concern OMT?
I appreciate your time


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## Droach6498 (Nov 1, 2020)

Droach6498 said:


> None of those pressures are a concern.


I have a freshly rebuilt 67400 bored to .070 eagle crank 4.25 lift aluminum heads Lunati cam 270/278 dur pistons are low compression so I can run 94 octane I put in some 91 it runs fine, so nothing radical but the oil pressure is 90 at idle and 90-100 o.p. running this is with a elec sensor at the filter Im thinking of getting a mech sensor the engine has about 50 miles on it is this a concern OMT?
I appreciate your time
[/QUOTE]


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## BearGFR (Aug 25, 2008)

That's a lot of pressure. Is that "cold" or after the engine is thoroughly and completely warmed up? Which oil are you running?

If 'cold', and you're using a heavy oil, that's not necessarily bad.

If warm/hot then I'd be looking for a reason. For one thing, it could be putting a lot of stress on the distributor drive gear creating a risk of wearing it out prematurely. 

First things first: Make certain that reading is accurate. It might be worth investing in a different gauge and sensor, installing the sensor into hole where the oil gallery plug that's on the top rear of the block, near the distributor, is now.

If the reading is accurate, and you know you don't have a pump that's supposed to put out that kind of pressure, then it's time to remove the oil filter housing on the side of the block and look for problems that might explain what's going on, or (sorry to say) inspect the check ball / pressure relief spring in the oil pump itself for a problem such as a jammed check ball/pressure relief spring - and that means pulling the engine to get to it.

Bear


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## Jared (Apr 19, 2013)

I'd recommend plumbing in a mechanical pump to verify the high reading on your electronic gauge. Nice looking engine bay BTW.


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## Droach6498 (Nov 1, 2020)

BearGFR said:


> That's a lot of pressure. Is that "cold" or after the engine is thoroughly and completely warmed up? Which oil are you running?
> 
> If 'cold', and you're using a heavy oil, that's not necessarily bad.
> 
> ...


So I purchased installed a o.p. gauge its 70 at idle. Still to hjgh?


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## cimager714 (4 mo ago)

Nice looking engine.


Sent from my iPhone using Tapatalk


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## Jared (Apr 19, 2013)

Droach6498 said:


> So I purchased installed a o.p. gauge its 70 at idle. Still to hjgh?


Is that when the engine is cold? Does it drop any when it warms up? Mine is close to 70psi at idle when first started up. Drops to a little less than 40psi at idle when hot and bumps up to ~60 by 2000 rpm when hot. I'm running 15W 50 weight oil. Hope this helps.


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## Droach6498 (Nov 1, 2020)

Jared said:


> Is that when the engine is cold? Does it drop any when it warms up? Mine is close to 70psi at idle when first started up. Drops to a little less than 40psi at idle when hot and bumps up to ~60 by 2000 rpm when hot. I'm running 15W 50 weight oil. Hope this helps.


How old is the rebuild, miles on it. Mine is about 50 miles. The problem I have is say I remove the engine replace the oil pump and its still running high, then WTF? Thats the feeling I get as the o.p. is new why should it fail? I think theres may be something plugging a galley. I beleive the oil is 15/20 I'll look into it further, It runs the same cold or hot 70 cold idle goes up when driving to about 90.


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## Jared (Apr 19, 2013)

Droach6498 said:


> How old is the rebuild, miles on it. Mine is about 50 miles. The problem I have is say I remove the engine replace the oil pump and its still running high, then WTF? Thats the feeling I get as the o.p. is new why should it fail? I think theres may be something plugging a galley. I beleive the oil is 15/20 I'll look into it further, It runs the same cold or hot 70 cold idle goes up when driving to about 90.


1300 miles. Initial start up was just about a year ago. No changes in oil pressure during that timeframe.


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## Droach6498 (Nov 1, 2020)

Jared said:


> 1300 miles. Initial start up was just about a year ago. No changes in oil pressure during that timeframe.


20/50 oil in engine currently


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## Sick467 (Oct 29, 2019)

Thicker oils tend to raise oil pressure. Not sure if they would raise it as much as you are seeing. I ran 10W40 for many years in my V8's, but have changed to 15W40 in the last few years. 50 weight seems thick to me depending on how your engine was built. I'd try some 40 weight.


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## Droach6498 (Nov 1, 2020)

Sick467 said:


> Thicker oils tend to raise oil pressure. Not sure if they would raise it as much as you are seeing. I ran 10W40 for many years in my V8's, but have changed to 15W40 in the last few years. 50 weight seems thick to me depending on how your engine was built. I'd try some 40 weight.


Yeah that and chage the filter I really dont think its the pump but plugged galley then pan leaked bad upon first install reinstalled he engine now r & r the engine gain almost puts me in tears
If it is a plugged galley where would it be? Im thinking a head gasket?


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## Droach6498 (Nov 1, 2020)

I was just thinking I have 2 oil filter housings, one has the bypass which is the one installed, the other is ffrom Kauffman has no bypass I think thats what its called the metal object inside the housing. Is that a good idea will probably be difficult to remove even if I can the housing as I have headers
Thanks or your help


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