High oil pressure z22/L20

[DatsunTherapist]

I have a 1970 Datsun 510, z22 bottom end with l20b head Frankenmptor.  Purchased the car second hand and didn’t do the initial work. I’ve noticed the oil pressure runs consistently high exceeding 100psi at 3500-4000rpm. My gauge only goes to 100 but the needle goes past to what would probably be 120. Recently switched oil to 5w-30 to try and lower the pressure but didn’t seem to help. Car idles between 60-70 after being warmed up for about 20 minutes. Car is located in SoCal so relatively warm weather most of the year. Any recommendations to drop the oil pressure to comfortable psi?

[datzenmike]

Probably the gauge. I've had many L series engines and at best, at idle, perhaps 30 is the best it can manage. The pump is regulated to 50-60 PSI but at idle the oil bleeding out past the main and rod bearings is more than the pump can produce.

 

I have had the regulator stick because of a small piece of casting that got loose. Around town was fine but out on the highway it would blow the oil filter. 

 

Get or borrow another oil pressure gauge and see.

[DatsunTherapist]

The gauges are brand new and were replaced with new oil pressure line as well. The previous original gauge showed the same pressure. Might it possible that there is a high pressure oil pump installed on the car? Learning as I go and trying to trouble shoot. 

[datzenmike]

New means nothing other than it's unknown. Oil pressure is 50-60 PSI. Never higher. It's not possible for a stock pump to make 60 PSI at proper idle. If idling at 2000 it might reach the regulated pressure of 50/60 PSI but shouldn't go higher. You should remove the pump and take the regulator out of it and make sure it isn't jammed. There's a large nut with a spring behind it with a sliding piston in front of that. Oil pressure pushes the piston against the spring. At around 55 PSI the piston compresses the spring and moves back opening a port that recirculates the oil stopping any increase in pressure. On mine, a piece of grit had jammed the piston and it couldn't move and the pressure split the oil filter.

 

 

Possibly a previous owner shimmed the relief spring so look for a spacer or washer under the spring. Generally the rule is 10 PSI for every 1,000 RPM expected. The Z22's 93mm stroke 'red line' is 6,500 so 65 PSI is MAX. 120 PSI is insanely wrong if the oil filter splits open.

 

 

Never run a 5w oil. 10w30 is fine. 5w is a thinner oil at colder temperatures so it gets to the bearings faster. Shouldn't be used above 60F. I wouldn't use it at all. 10w30 is good to 0 F.

[DatsunTherapist]

Just to give you an update. Problem was the gauge. Oil pump is going fine. Seriously can’t believe it was just a faulty gauge. Thanks for the help. 

[datzenmike]

Glad you found it.