High Oil Pressure 1966 390hp

[Brian M.]

I own a 1966 coupe with the 390hp engine. I recently restarted the car after it had been stored and not run for 6 years. The engine sounds good and runs strong and everything seems fine with one exception. The oil pressure gauge seems to be reading very high. On startup with the engine cold at fast idle (900rpm) the gauge reads full scale (80lbs plus). When the engine reaches operating temperature the gauge drops to 35lbs at idle (750rpm) but when I rev the engine to 2000rpm or on the highway cruising at 2000rpm the gauge reads 65 to 70 lbs. This seems much higher than when the engine was last running 6 years ago. The engine does have a high volume oil pump but I am sure the readings are much higher than when I last drove the car. The only thing I am doing differently is I am using a lighter oil. I thought it would be good to start up with a lighter oil so I put in 10w30 (Quaker State) instead of the 20W40 or 20W50 Castoral or Valvoline I normally use. Oil is definitely getting to the top of the engine as when I take the oil filler cap off I can see it pumping up from the lifers.

Any idea what could be causing this? Is there anything that could be restricting flow in the engine to create higher back pressure? Any danger of doing damage to the engine or does it sound like a gauge problem?

Any advice is greatly appreciated.

Brian Millar

[Duke W.]

Re: High Oil Pressure 1966 390hp

What is the hot oil pressure for your engine listed in the AMA specs?

Why are you using SM oil?

Duke

[Brian M.]

Re: High Oil Pressure 1966 390hp

What is the hot oil pressure for your engine listed in the AMA specs?

Why are you using SM oil?

Duke

Sorry I don't have answers for either of your questions, I don't know what the AMA specs say. What type of oil do you feel I should be using?

[Danny P.]

Re: High Oil Pressure 1966 390hp

sound normal to me, it will alway go high when cold as the engine warm up it should drop a few lbs. you should worry when there no pressure

[Joe L.]

Re: High Oil Pressure 1966 390hp

What is the hot oil pressure for your engine listed in the AMA specs?

Why are you using SM oil?

Duke

Duke and Brian-----


Normal oil pressure for the application is 50-75 lbs.

[Tom O.]

Re: High Oil Pressure 1966 390hp

I have a '67 427/390 with the high pressure oil pump, but a 0-60 psi gauge. You readings are similar to mine. I have used 10W-30 and 20W-50, both approximatley reading what you are getting. Of course, on start up my gauge is pegged until the oil warms up.

[Duke W.]

Re: High Oil Pressure 1966 390hp

. What type of oil do you feel I should be using?

Search the archives for "CJ-4". Take some time to go to the referenced educational sites to learn about motor oil.

Duke

[Mark H.]

Re: High Oil Pressure 1966 390hp

Tom,

Saw you Oct 2006 msg below :

" I have a '67 427/390 with the high pressure oil pump, but a 0-60 psi gauge. You readings are similar to mine. I have used 10W-30 and 20W-50, both approximatley reading what you are getting. Of course, on start up my gauge is pegged until the oil warms up."

How did this turn out for you. I have the same "problem". I 've got a new motor with the same symtoms you discuss (65 SB/350 HP with a 60 psi gauge). It too is pegged until warm and then comes down to mid 50s. My builder a s s u r e s me a non-high volume Mellings 55 pump was used - pressure still too high I would think. Your engine holding up OK to the continual high pressure at start up ?

Thanks,
Mark

[Tom O.]

Re: High Oil Pressure 1966 390hp

"How did this turn out for you. I have the same "problem". I 've got a new motor with the same symtoms you discuss (65 SB/350 HP with a 60 psi gauge). It too is pegged until warm and then comes down to mid 50s. My builder a s s u r e s me a non-high volume Mellings 55 pump was used - pressure still too high I would think. Your engine holding up OK to the continual high pressure at start up ?

Thanks,
Mark"


Mark,

So far, in the five years I have had the car and since its overhaul/restoration around 1990, it has done fine with the high oil pressure. However, last year I had an intermittent knock that turned out to be a scored number one main bearing. Looked as if something got in there and messed up that bearing only. The crank journals were O.K. And that was when I was using Mobil 1 in it. At my Corvette expert's advice, I am using 20W-50 but the pressure gage stays around the same readings as with the synthetic.

Tom

[Mark H.]

Re: High Oil Pressure 1966 390hp

Thanks for the info Tom.

This has been a frustrating item for me. I have just a many good people saying 50-60 psid is too high as those that say it's fine (even though on the high side). Your info gives me some comfort when the gauge is pegged when cold. Hopefully it will loosen up some in the miles ahead.

Mark

[Tom O.]

Re: High Oil Pressure 1966 390hp

Mark,

The man who told me to use 20W-50 is truely a Corvette expert and certified master mechanic. He knows the old ones from top to bottom and has done numerous body off frame restorations (6 last year). I do what he says because I don't know anyone around San Antonio that knows more than he does. He has driven my car on several occasions after he worked on it and I do not recall him ever mentioning the fact that the gauge was pegged.

I'm no expert but I would rather have high oil pressure rather than low.

As to it coming down with use, I am guessing my car has around 10-12,000 miles on it since the engine was overhauled and still pegs the gauge.

Good Luck,

Tom