Thread: Oil pressure issue

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So I picked up a 1975 Datsun 280z with a 350 swap. The car sat in duds garage for around 15 years. Y exactly I'm not sure, any way the engine fired with no issues, but once it warms up the oil pressure drops drastically low 5psi. But while in the throttle the pressure still builds and seems to hold. Is this normal? Or do I have an issue?
I have been told a few different things,
1) oil pickup might be clogged
2) oil pump is failing
3) the piston rings are bad
4) the gauge is bad, but it's a direct reading gauge.

Any advice? I plan on pulling the engine and taking it one theory ata time if I can get a solid answer.

Thanks for the help.

This is a subject of many facets and many opinions. My experience is that a stock small block Chevy in good condition will have around ten to fifteen pounds oil pressure at idle when warm, and the pressure will increase with engine speed up to between forty and sixty pounds, and also decrease with engine speed on deceleration. This make some folks uncomfortable, and they go to all sort of lengths to increase the oil pressure. Now, five pounds at idle would seem to be a bit low to me, but not panic time low, just needing some attention. The first thing I would do would be to change the oil and filter, and find another gauge, probably just buy a new one as they are not too costly, to connect in place of the one you have to compare; make sure there are no kinks or flat spots in the tubing going to the gauge, perhaps remove the tubing and clean it and the port in the block out. Depending on how much wear the engine has, it may be worn to the point that clearances are too wide to hold normal pressure at idle. The rings won't have any bearing on oil pressure, but they will contribute to oil usage; worn bearings will have an effect, though - also some form of restriction in the oil passages. Others will have differing opinions, so keep an open mind and consider all that you read here. Several of the members here are full time engine builders, and have many years of experience; me, I just hang out under the proverbial shade tree.

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Welcome Aboard, it's good to see you here.
Rrumbler tells it straight. 5 psi at idle when hot is low but not 5 alarm fire low.. I'd replace the motor oil and filter ( I prefer synthetic motor oil ) and he suggests replacing the oil psi gauge. We don't know if the current gauge in place is mechanical or electrical, but I would suggest getting a mechanical test gauge that replaces the unit in place on a temporary basis. Just to verify the validity of the readings your getting now.

He is also correct on the rings topic. And I'd say if it can make even 15 to 20 pounds of oil pressure, I wouldn't worry about it for now. Use the motor as is and feel the car out and see what other things will need repair / replacing / changing etc..

This will help you make a plan without any surprises (hopefully) and have a car you can enjoy.

Welcome!
Without knowing the type of cam that is in the motor, I'd recommend an oil with high zinc to protect a flat tappet cam. And keep in mind that synthetic oils will often run slightly lower pressures.

I will add, to make sure oil is getting up to your rocker arms!

Welcome1.jpg

I can't add anything more of value other than to echo 36 sedan's comments about oil, and welcome you to the forum. Not knowing if you have a flat tappet or roller lifter cam, I'd strongly recommend that you err on the side of caution and use a good, high ZDDP racing oil like like Brad Penn's. I am not a big fan of synthetics myself, but I'm not saying they are bad.

There was a flap a while back about Fram filters causing problems, so I would change oil and use a premium NAPA filter (I think they're Wix). As far as the roller/flat tappet cam issue, for now I'd use an off-the-shelf oil and add a bottle of ZDDP to the oil. Roger's suggestion of using Brad Penn oil that has ZDDP in it will work also. If you find out in the future that the motor has roller cam and lifters, discontinue the use of the ZDDP and use plain old off-the-shelf oil.
Isky ZDDP Plus Additives ZDDP - Free Shipping on Orders Over $99 at Summit Racing

Read this tutorial to bring yourself up to speed concerning flat tappets and the need for ZDDP....
http://www.crankshaftcoalition.com/w...ips_and_tricks

If the swap was done with maintenance in mind (not likely), you may be able to pull the oil pan and change out the bearings. I never did like doing it that way, preferring to pull the motor and do it because if the bearings are gone, chances are the rings are toast also.

You can find out a little more about the motor by performing a compression test.....
Use a screw-in type gauge.
Bring the motor up to operating temperature and shut off.
Remove the air filter assembly.
Wire the primary throttle blades wide open.
Remove spark plugs.
Disable coil to prevent a fire.
Turn the motor over with the starter through at least 5 cycles on each cylinder to make sure you have maxed the gauge for that cylinder.
Post the results here.


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Thanks so much for the troubleshooting tips! I hope too have the car in the garage this weekend. And i will begin with the most basic step and go from there.

I hadn't seen this replyed yet but just making sure your not using a light weight oil? yes it will need zddp but if you are using 10w30 or thinner weight these flat tappet cammed motors where never designed to use a light weight oil (which also drops your pressure) as todays motors do. Check out Bad Penn 20w50 as Roger mentioned if not wanting to add zddp as an additive as its pretty economical. The old rule of thuimb I always heard is 10lbs of pressure fror every 1000 rpm's on a sbc, depending on what you want out of this motor, if its a occasional driver (no hard racing or high reving etc) you could step up to thicker oil and probably never have to touch this thing, I ran the same low pressure on a old pickup for 60-70 k miles or so as a daily driver (thats a long time for occasional driving) and sold it, probably went that many miles after I sold it! Don't get to alarmed just have fun Matt