Oil Pressure high?

[Wowed777]

my 1973 corvette was running at 15 psi at idle and 35-40 psi when running. I changed the Oil and filter last night and it now idles at 40-45 PSI. I used 10w-40 standard oil. the engine was not warm and it was 60 degrees outside.

Is this very high? why would the change cause such an increase?

 

[Bob Chadwick]

Did you let it get warm? My 77's oil pressure ran somewhere around there at idle when cold but dropped back down once the engine heated up.

 

[Wowed777]

oil pressure

I didn't let it warm up too much. When I saw the jump, I thought it was unusual and didn't want to run the engine too long if there was a blockage or other issue that would cause a larger issue. The numbers seemed reasonable before I did the oil change 15-20 at idle and 35-40 (cold and warm) running.

Now it started at 40-50 psi at idle.

Why would it jump in pressure with nice new oil? I would have thought the pressure would go down as the old oil was thick and dark.

 

[Vettehead Mikey]

40-50psi at idle with cold oil is normal. I'm surprised you didn't notice before.

I hope the new oil has sufficient ZDDP to protect the cam. Most modern oils don't.

 

[Wowed777]

I used Valvoline Premium conventional and a Fram tough stuff filter. I was thinking about replacing the Fram with WIX. I know there are lots of opinions on this topic. Should I change the oil? I don't know how many true miles are on this engine (got the car recently), but its a chevy 3970010 block.

 

[Hib Halverson]

Valvoline...great oil.
Fram...junk filter.

Wix or ACDelco Ultragard are better. Also, the Bosch and Mobil 1 filters are quite good but costly.

 

[Vettehead Mikey]

That oil has an SM rating which is not suitable for a flat tappet engine. Either find a bottle of ZDDP additive or swap the oil for a CJ4 rated oil like Rotella auto/diesel oil that already has plenty.

 

[targatom]

zddp reduction for rotella diesel oil?

That oil has an SM rating which is not suitable for a flat tappet engine. Either find a bottle of ZDDP additive or swap the oil for a CJ4 rated oil like Rotella auto/diesel oil that already has plenty.

I read somewhere recently that Rotella Diesel oil, has reduced the amount of zddp in it, does anyone know if this is factual? They said that if you have a flat tappet engine that zddp should be added,, and that the original reason for zddp being removed is that it clogs cat converters. Anyone weigh in on any of this?

 

[Vettehead Mikey]

I read somewhere recently that Rotella Diesel oil, has reduced the amount of zddp in it, does anyone know if this is factual?

Not at all true. I have a statement from Shell, backed up by multiple independent samples.

 

[mr.beachcomber]

my 1973 corvette was running at 15 psi at idle and 35-40 psi when running. I changed the Oil and filter last night and it now idles at 40-45 PSI. I used 10w-40 standard oil. the engine was not warm and it was 60 degrees outside.

Is this very high? why would the change cause such an increase?

To really answer your question, we need to know which engine you have in your '73, base SBC, L82, or LS4 BBC and how many miles are on the engine itself. Secondly, what grade oil were you changing, e.g., 10W-40, 10W-30? How many miles were on the old oil when you changed it? Did the old oil smell of gasoline or by-passed combustion products? Does the engine use oil between oil changes? If so, how much?

Although I don't know the answers to the above questions, my first impression upon reading your post was that your likely had a high mileage, base SBC whose oil had sheared out of grade either from fuel dilution or excessive miles on the oil (or both). Adding the new 10W-40 just brought the idle PSI back up to where it should be. (If you have either the L82 or LS4 engine, the idle PSI is low as both engine have high performance, i.e., higher PSI, oil pumps.)
Thanks!