Pinned the oil pressure gauge

Took the '66 out for a spin and noticed the oil pressure gauge had the needle pinned! Nothing outta the norm the way the car ran. The pressure is usually up there but never really pinned. It was chilly this morning but not THAT cold. Any thoughts on why this would be?

Probably a shorted wire or kaput pressure sensor. At least I hope so....

You've probably been reading my own thread too much and you've caught the car killer cooties now...

Rich Z said:

Probably a shorted wire or kaput pressure sensor. At least I hope so.... ...

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Thanks, Rich. Being this is a mechanical oil pressure gauge I only see the copper tube from the engine to the rear of the gauge, and wiring I checked doesn't have anything to do with the gauge itself (only wiring I see is for the light). So when you say sensor you mean the gauge, right?

P.S. I edited this for clarity.

RedRestoredRoadster said:

Thanks, Rich. Being this is a mechanical oil pressure gauge I only see the copper tube from the engine to the rear of the gauge, and wiring I checked doesn't have anything to do with the gauge itself (only wiring I see is for the light). So when you say sensor you mean the gauge, right?

P.S. I edited this for clarity.

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Sorry, I just assumed that you were getting an electrical signal from an oil pressure sending unit somewhere on the engine. Never having had a C2, I don't really know how they are set up.

In any event, here's an interesting page for you to look over -> http://lubricants.s5.com/oil_pressure.htm

Just out of curiosity, have you changed the oil and filter recently?

Rich Z said:

In any event, here's an interesting page for you to look over -> http://lubricants.s5.com/oil_pressure.htm

Just out of curiosity, have you changed the oil and filter recently?

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Very interesting and informative link, thanks.

Yes, I did change the oil recently! I used either GTX 10w40, or Penzoil 10w40 (I am sure of only the weight). Too thick an oil perhaps?

RedRestoredRoadster said:

Very interesting and informative link, thanks.

Yes, I did change the oil recently! I used either GTX 10w40, or Penzoil 10w40 (I am sure of only the weight). Too thick an oil perhaps?

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Well, a general rule of thumb is that if something starts going wrong, think back to consider if anything you did prior may be have caused the problem. Those oil weights you indicate don't seem excessively heavy weight to me, but normally I believe 10w30 is what is commonly used. Generally speaking, heavier weight oil can cause higher oil pressure, and lighter weight oil can give you less oil pressure. Personally, I would tend towards the lightest weight oil available since low oil pressure usually means better oil FLOW. Higher pressures would likely mean that your oil pump is working a lot harder than it should be as well.

Of course, this is all presuming that your engine is in generally good shape...

Rich Z said:

Well, a general rule of thumb is that if something starts going wrong, think back to consider if anything you did prior may be have caused the problem. Those oil weights you indicate don't seem excessively heavy weight to me, but normally I believe 10w30 is what is commonly used. Generally speaking, heavier weight oil can cause higher oil pressure, and lighter weight oil can give you less oil pressure. Personally, I would tend towards the lightest weight oil available since low oil pressure usually means better oil FLOW. Higher pressures would likely mean that your oil pump is working a lot harder than it should be as well.

Of course, this is all presuming that your engine is in generally good shape...

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It's been reading high @ 60 PSI (max for the gauge) for YEARS and then more recently with the cooler weather it pins the gauge but the engine has always run as strong as! I used 10w30 in NY but changed to 10w40 since in FL. I will change the oil tomorrow and try 0w30 or a 5w30 and see if that makes any difference. According to the link you provided in your earlier post and as you commented here, lighter weight oil allows for better flow. I'll give it a try. Thanks.

Yeah, I've talked to people who were under the impression that the higher the oil pressure, the better. I don't subscribe to that theory. Higher oil pressure just means that the oil pump is working harder to produce the oil flow it was designed to deliver.

If you look at most indicator dials on cars, normally the indicator mark dead center is what is considered as average and normal for the reading expected to be displayed there. I'm presuming that this is by design and not just a random selection by the design engineers.... So that would be the target I would shoot for to consider what is NORMAL. This is presuming a STOCK engine, and the one that came originally in the car, of course...

Higher oil pressure equals less power as well. I like the pressure between 30 & 60. To thick of a weight is also a power robber unless the bearing tolerance are looser (we build the drag motors 5 thou looser than street motors) and then we run a slightly heavier oil.

Rich Z said:

I'm presuming that this is by design and not just a random selection by the design engineers.... So that would be the target I would shoot for to consider what is NORMAL. This is presuming a STOCK engine, and the one that came originally in the car, of course...

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Funny you say that! The engine is the original engine but was rebuilt 11,000 miles ago and from what I was told, part of the rebuild was mild cam work, and valve work to accommodate the use of unleaded gas. I was told in my search for an answer to this problem that it was common on engine rebuilds to buy the high volume Melling or the Z28 pump and then shim the relief valve spring to raise the system pressure. Damned if I know if that was done. Possible cause for the high pressure readings?

RevXtreme 1 said:

Higher oil pressure equals less power as well. I like the pressure between 30 & 60. To thick of a weight is also a power robber unless the bearing tolerance are looser (we build the drag motors 5 thou looser than street motors) and then we run a slightly heavier oil.

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In your opinion could 10w40 oil be the problem? and if/so would 10w30 or 5w30 make any difference?

My high oil pressure readings have lead me to inspect the by-pass valve. Perhaps what I noticed is of no consequence to the matter but I want to put it out here just in case.

OK- Here it goes!
1st picture shows the area where the by-pass plate gets installed. Notice the hole in the block.

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2nd picture highlights the by-pass in the plate. Also highlighted is an "X" stamped at the opposite end of the plate.

My question(s) ... Should the by-pass get positioned in a certain way? Should it be as close to the hole in the block as possible? When I removed it for cleaning/inspection the by-pass was at the opposite end of the hole in the block and the "X" was closer to the hole in the block.
Also, what I found of possible interest ... the by-pass plate's mounting bolts were different, which leads me to believe a previous owner was messin' with this set-up at one point.

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Thanks to all who have helped with input and information.