I have a 68 with a 350 engine. When I fire it up I get about 60 PSI. When I'm driving I average 45 psi. After its warm and I idle at a stop light it drops to 15 or less. I can rev up at light and increase it to over 20. I'm using Lucas classic 10w30 w/zinc. Any ideas? Thanks

 

Stock gauge? Not the most accurate things in the world.
I wouldn't worry too much at this point as long as there's no noise like lifters rattling.
You could switch up to 20/50 and see if that helps.
How many miles on the engine?

 

Thanks for the reply ,I think I will change the gauge. No abnormal noise in engine. I'm not sure how many miles but I assume a lot. If the new gauge reads the same I will try your oil suggestion. Thanks again.

 

Try a hand held gage first (Tool). The gages that you buy for the dash are not calibrated. You should do the low end test at near 1000 RPMs. Your car may idle under that but it should not be working under that. 90% of the cars I have worked on that came in with Low Oil Pressure and no other symptoms end up just being a gage issue. GM valve system are very touchy. If you have real low oil pressure the engine will rattle.

Rule of thumb: you need 10 PSI per 1000 RPM under load. If you run less then that you may damage the motor. It is normal for oil pressure to drop as an engine wears and its also normal that it shows up at low RPMs first. Anything you do within reason to raise oil pressure will increase the life of the motor. I normally will run 20w50 in a motor long before I would think about refreshing it. My next step on a non-race engine would be a good high volume oil pump. I have seen that add years to a daily drivers.

Course if you like to drive around at 6500 RPMs all the time you may want to inspect the motor to make sure that the issue is not lower end bearing clearances. I would just pop the pan look for metal, plastic gage a rod and a main bearing. If they are to spec replace the oil pump and be done for awhile.

 

Gorn, that's some really good advice. I appreciate you taking the time.

 

OP,, if a new, accurate, gauge shows same PSI (15 at idle) the Oil P is fine. Gorn note on 10 psi per 1k rpm is the norm. 10-15 psi at 750-800 rpm at idle is fine.

20-50, as noted, is fairly common switch on motors that have some higher milage wear, or were built with wider bearing clearances (fairly common on performance builds) so try that if in fact your OP gauge is reading right.

Magnetic drain plugs are handy to collect any engine wear and if you have whickers on one....that shows something is wearing. Blackstone Lab can do oil analysis which will show, among other criteria, what metals are present (bearing material).

 

5 pounds turns on the idiot light
15 at hot idle is slightly low but okay (about normal)
Use a direct pressure gauge to test it accurately.

 

I used that oil designed for older high mileage cars and it brought it up. These older engines were not that tight to begin with and especially after a few miles on them.

 

You need to worry when the hot idle oil pressure drops down to 5 or 8 psi
That is when the idiot light comes on (at 5 pounds)
15-20 hot idle is fine or good IMO
And 60 cold is plenty for a stock motor
The better (direct pressure) gauge will sure be a bonus