Oil pressure drops on C2 L79

[David M.]

I notice occasionally the oil pressure drops from 40 to 20 after the engine temp gets to around 200. This happens when idleing at stop light but not while driving. The engine is 327/350hp. The oil is Mobil 10-30. Should I go to 20-40 during the summer months? I live in AZ.

[Russ S.]

Re: Oil pressure drops on C2 L79

Sounds normal to me.

[Joe L.]

Re: Oil pressure drops on C2 L79

I notice occasionally the oil pressure drops from 40 to 20 after the engine temp gets to around 200. This happens when idleing at stop light but not while driving. The engine is 327/350hp. The oil is Mobil 10-30. Should I go to 20-40 during the summer months? I live in AZ.

David------


What you describe is completely normal. As far as an oil viscosity change goes, it won't hurt but I don't think it's necessary based on what you described.

[Michael H.]

Re: Oil pressure drops on C2 L79

I would try Mobil 1 20-50 especially in your hot climate.

Mike

[Mark E.]

Re: Oil pressure drops on C2 L79

As already stated, your oil pressure is normal, in my experience.

Not to start the oil discussion again, but Mobil 1 15w-50 increased pressure during hot idle by 10 PSI compared with 10W-30 in my 454. It also has the required zinc/ phosphate for these engines.

A larger oil filter will also increase oil pressure a bit. Try PF35 or even PF932 if there's room.

[Duke W.]

Re: Oil pressure drops on C2 L79

The Chevrolet oil pressure spec for your engine is 40-45 psi at 2000 engine revs an up on a fully warmed up engine.

Chevrolet does NOT have a spec for idle oil pressure, but depending on idle speed it's usually in the range of 15-30 psi, the higher the idle speed the higher the pressure, and depending on engine type the range is about 450 to 1200.

Assuming your L-79 has an OE equivalent camshaft it should idle with decent quality, but a slight lope at about 750.

The biggest problem you have is likely the wrong type of oil. You should be using C-category, not S-category. Put the following phrase into a search engine:

"engine oil for vintage corvettes"

Include the quotes so it looks for the whole phrase, not just the words.

Duke

[Mike T.]

Re: Oil pressure drops on C2 L79

David - As has been pointed out, the pressures you're seeing are within tolerances but am a bit curious about some details. Any idea how many miles on your L79? You did say the drop was from 40 down to 20 while at idle and after it reaches up around 200 degrees, is this a new development or just something you've noticed now that the temps are moving upwards? For oil, I've been using CJ-4 and CK-4 15-40 that's offered by just about everybody. I started out using Shell's Rotella in those designations because it was determined to have enough ZDDP to help flat tappet cams but early on, found out that the same grade of oil (CJ-4/CK-4) was available at a lower cost from places like Walmart.

[David M.]

Re: Oil pressure drops on C2 L79

Mike, great questions. The odometer (which I believe is correct) says 75 k miles. I believe the engine was rebuilt before I purchased the Vette to run better on unleaded gas. I have had it for approx 15 years. I notice the oil pressure drops with the summer heat and when I am running the factory a/c. I have noticed the same issue in past summers. I think I am leaning towards using a heavier weight oil and see how that does. Stay cool in Prescott.