oil pressure question

[az1966]

I have a 66 coupe, 200 ci motor, 3 spd manual tranny,,,,lately the oil pressure guage has been sitting at a hair lower than the half way mark and as the motor warms up the guage starts sinking to about the 1/4 mark ( hot as all get out in Phoenix arizona),, I understand oil thins out as it warms up, but I'm using 10-40 valvoline synthetic oil, needless to say if if drops to far it's a disaster,, question is is how far is to low? should I switch to 20-50 weight,,, the low end of the motor has never been rebuilt and I'm thinking oil pump replacement,, no knocking or rattling yet,,, any input would be appreciated

 

[PaulS]

Put a master gauge on it to find out exactly what the pressure is.
You really don't know if the pressure is low, the sender id going bad or the gauge is losing accuracy.

 

[rbohm]

8) the minimum oil pressure you should see is 20psi hot, and then 10psi per thousand rpm, again hot. if you put a proper pressure gauge on and find your pressure a bit low, then step up to a 20w-40 oil, or even switch to a straight 30 weight oil. but that is only if you see at least 15psi hot. less than that and you need to drop the pan and check to see if the pressure relief valve is working properly, and perhaps add a shim to increase the spring rate.