Oil Pressure - is this normal?

[ND67]

I had my Vette out this weekend and noticed that at 65MPH the oil pressure is almost pegging 60psi. I have a 327/300 and was driving on a relatively warm (muggy) summer day. What’s the rule of thumb regarding oil pressure? Is it possible that the engine was overfilled with oil at the last change? I have always thought that driving at a high speed on a hot day resulted in lower oil pressure.. not higher.

Any ideas?

Thanks,

ND67

 

[mcditalia]

Well, I can tell you that upon start up, my 350 horse 327 pegs the meter close to 60psi or so, but eventually, as the car warms up and is driven it settles at around the 45psi mark. (if I remember correctly). If your car's meter is constantly pegged at 60psi then something is wrong, especially if you have a 327 and not the big block (which should have higher oil pressure). If you overfilled the motor with oil it could be a reason, did you check the level? If not it could be as simlple as a gauge related problem or worst scenario a motor problem.

 

[ND67]

Thanks for the reply mcditalia. I did check the oil level a few days before and it was at the full mark. Upon re-thinking this the car was warm but not hot. I let it idle in the driveway then checked the oil.. it began to rain so I pulled back into the garage. I'll drive it again (once this rain stops) and re-check the oil level.

You mentioned that your 327/350 settles around 45psi. Is this considered normal? For some reason I had thought that 30psi was normal so I was concerned. My engine was rebuilt two years ago and runs fine, I just happened to notice this and it seemed odd.. especially on a hot day. The pressure is not always at or near 60.. just when I jump on it and maintain a high speed.

I'll recheck the oil level and do some more testing.

Thanks Again.

ND67

 

[Tom Bryant]

60 psi or even more is normal for an engine with a high pressure oil pump. In any case your oil pressure will climb with rpm. It is normally lower overall when at operating temp but it will still climb with increased rpm.

Sounds to me like your rebuilder installed a high performance oil pump. That is not a bad thing. Pretty common for a performance engine. I never use standard oil pumps in a performance engine. I used to use the '67-'69 Z28 pump in everything small block. 60 psi was what I expected going down the road with that pump.

Tom

 

[allcoupedup]

My 327 registers about 30 psi at cruising speed when warm. At operating temp idle pressure is about 20 psi. I don't sweat it as the engine is quiet (no rod or valve noise). I have no idea how many miles this engine has on it.


Do high pressure oil pumps really add that much value for street applications?

Thanks,
brian

 

[Tom Bryant]

No. They are more for insurance on high rpm engines. I prefer a high volumn to a high pressure but high volumns will usually get you 60 lbs. My old '86 Jimmy with a 2.8 V6 ran 60 lbs cold and 45 warm when it was new. This was standard for that engine. My '03 Vibe runs around 65 cold. I think they are going to higher pressure for insurance on these new little engines that have to work harder. Actually a stock street engine will live well on half of what you have. Even 5 lbs at idle will do the job. Before 1953 Chevy sixes had splash oiling like a Briggs and Straton lawnmower. They lived well on that system.


30 and 20 is what a good stock 283/327 would run back when they were new.

Tom

 

[Driftwood]

My 69 350/350 originally was running at 35psi. While changing the oil pan gasket, rear seal, etc. I also replaced the oil pump with a standard volume & pressure Melling M55 pump. The pressure jumped to 55psi. Possibly over time the oil pump teeth wear and reduce the pump's output pressure. If the 327 had a similar oil pump, your pressure sounds low to me.

I would drop the oil pan and replace the oil pump-- it's a very simple procedure. I would also install a new 1 piece Felpro oil pan gasket, if available for the 327.

My 2 cents.

Andy

 

[ND67]

Guys,

Thanks for all the replies. I'm learning a lot.

Tom- how can I tell if the oil pump is high pressure or not? Does it look any different? Larger? You can tell I'm new to this...

ND67

 

[Mac]

The other thing to be aware is the oil pressure gauge may not be properly calibrated so your 60 psi might not be so high, so to speak.

 

[Tom Bryant]

Guys,

Thanks for all the replies. I'm learning a lot.

Tom- how can I tell if the oil pump is high pressure or not? Does it look any different? Larger? You can tell I'm new to this...

ND67

Pump pressure is regulated by the internal bypass spring tension. Stronger spring = higher pressure. High volumn may have larger diameter or longer gears which would make the housing larger. You would have to have an original to compare qnd of course you would have to pull off the oil pan.

Might be easier to look on your bills from the engine rebuild or ask the rebuilder.

As Mac said your oil pressure guage could be off too.

Tom

 

[allcoupedup]

The comment about the accuracy of the stock oil pressure gauge is right on. These things are notorious!

When I purchased my first (and only) midyear I was an uninformed, nervous, excited mess and it wasn't until I got home did I notice the oil pressure reading 5 psi at idle and 15 at cruising.

I thougt I had been ripped off but questioned the reading since the engine was quiet and smooth. I disconnected the oil pressure line at the dash gauge and hooked up a nice gauge from grainger. No sweat - as mentioned earlier it was OK.

I recommend T-ing off the oil pressure fitting at the back end of the block so you can hook a precision gauge up for periodic sanity checks. I couldn't getthe little fitting off due to intake manifold clearance so next time I have the intake off I'll have a T connection.

 

[vette-dude]

Suggest that anyone changing over to a high volume or high pressure oil pump that you also use a steel coupled drive shaft for the pump. The little plastic retainer on the stock oil pump drive shaft will not live long on the new pumps. They only cost about $10 and are good insurance against a oil pump drive shaft failure.

Randy

 

[JohnZ]

I've been building SB's for 40 years, and have never used anything but stock oil pumps; the old SB has an extremely effective and highly-developed oiling system, and IMO doesn't need HP or HV pumps unless they're all-out race motors with external oil plumbing, coolers, remote filters, etc. Oil pressure is a function of bearing clearances (resistance to flow), and once you exceed the rating of the bypass spring it just dumps the excess in the pan anyway. I think HP and HV pumps for street-driven cars were invented by the marketing and finance executives at Summit and Jeg's

 

[Mac]

I think HP and HV pumps for street-driven cars were invented by the marketing and finance executives at Summit and Jeg's

Yup, they rate right up there with under-drive pulleys and snake oil. :L