oil pressure and temp gauge

[merlin3]

on my 509 merlin it has a high volume oil pump i just installed a new gauge cluster with a mechanical oil pressure gauge i am wondering why with engine running the needle is pegged all the way over and out of sight and engine off it reads half.also wondering what direction i should go with the temp gauge not working after trying 3 different senders.thanks

[BlackedOut67shorty]

For stock gauges you might have a 60lb oil pressure dash, you would need the oil pressure unit from a C50-60, they have an 80lb oil gauge, parts board might have one. Are you sure you connection is good going out to the sending unit, use a jumper wire and see if your gauge works.

[TBONE1964]

Originally Posted by merlin3

on my 509 merlin it has a high volume oil pump i just installed a new gauge cluster with a mechanical oil pressure gauge i am wondering why with engine running the needle is pegged all the way over and out of sight and engine off it reads half.also wondering what direction i should go with the temp gauge not working after trying 3 different senders.thanks

On your oil pressure issue, it is not uncommon for a BBC with the right combination of oil pump and bearing clearances to reach 100 + lbs of oil pressure cold. Remember that oil pressure and oil volume are two different things. Too much oil pressure is not always good and can cause oil leaks and even a twisted/broken oil pump drive.

However, a mechanical oil pressure gauge whether it is stock or aftermarket should return to zero when the engine is shut off. My bet is your oil pressure gauge is defective. Even with a good working 80 lb gauge, I am sure you will see high readings on a cold engine. You may also want to contact your engine builder and ask them what cold oil pressure should be.

On the temp gauge issue, what is the exact problem? Does the gauge not move up from cold at all? Does the needle peg to the right? There are several reasons for a temp gauge not to work. If you can provide some specifics, it will be easier to diagnose the problem.

Take care,
Tom

[merlin3]

i checked the copper tube coming from the motor and going to the oil pressure gauge it looks fine and i have a new gauge cluster.on the temp gauge the gauge never reads anything.thanks

[TBONE1964]

Originally Posted by merlin3

i checked the copper tube coming from the motor and going to the oil pressure gauge it looks fine and i have a new gauge cluster.on the temp gauge the gauge never reads anything.thanks

When you say "new gauge cluster" is it a new aftermarket cluster from a vendor like LMC or Brothers, or is it a restored original with some new aftermarket gauges. Some new aftermarket temp gauges do not use the external resistor and some do, depending on the manufacture. The factory GM gauges always use an external resistor.

Can you check the gauge for power with a 12V test light or a DVOM? You need to establish that the temp gauge is getting power from the ignition switch. The temp gauge shares its power with the fuel gauge and is a pink 20G wire that is located at pin 3 on the connector.

If the fuel gauge works ok but there is no power on the gauge, I would look at the printed circuit board and see if there is any bun spots.

If the temp gauge does have 12V on it, remove the green wire from the sending unit and touch it to ground. Do this very briefly and do not hold it to ground for very long. It is best to do this with help from someone to watch the gauge.

If you ground the green wire, the gauge needle should peg to the right. If it does not peg to the right and you are sure you have power, then I would suspect a bad gauge.

Make sure you have the ignition in the run position when doing these test. The engine does not have to be running.

Keep us posted.
Tom

[merlin3]

thanks tbone thats just the info i was looking for on the temp gauge.on the oil pressure gauge,i installed another gauge and it read 60lbs. then i took the new gauge out of the cluster,moved the needle back to the low position,started motor and watched the brass parts of the gauge get warped right over past high.the new cluster looks new not rebuilt.

[davepl]

I'd go buy a $20 gauge from the local parts store to sanity check it.

My LS7 dry-sump Vette runs 100psi when cold. I'm afraid of bursting a filter, but have been OK so far.

High volume pumps have bigger (taller) gears so they move more oil per revolution. High pressure pumps use a stronger spring on the relief valve. You can combine both.

If you kept tight rod clearances with a high volume pump I could see these kinds of pressures being expected. But the gauge not returning to zero does of course indicate some kind of instrumentation issue to sort out first before worrying about the rest...

[TBONE1964]

Originally Posted by merlin3

thanks tbone thats just the info i was looking for on the temp gauge.on the oil pressure gauge,i installed another gauge and it read 60lbs. then i took the new gauge out of the cluster,moved the needle back to the low position,started motor and watched the brass parts of the gauge get warped right over past high.the new cluster looks new not rebuilt.

What I think is your engine just puts out more oil pressure than a stock gauge can handle. Have you tried to test oil pressure with a different gauge? Look at this autometer that has a 150 lb limit.
https://shopping.yahoo.com/37868761-...xgmolQ?bfr=0.0

Something like this would tell you exactly what your oil pressure is.

I do have some 80 lb factory gauges in my inventory. I would be willing to send one to you for a test but it is going to be a while. I am preparing to move to Oregon from Michigan and have all of my gauges packed up.

[davepl]

I have a 60psi, is that the "normal" one? I knew there were 80s out there but am not sure what the standard unit is.

[TBONE1964]

Originally Posted by davepl

I'd go buy a $20 gauge from the local parts store to sanity check it.

My LS7 dry-sump Vette runs 100psi when cold. I'm afraid of bursting a filter, but have been OK so far.

High volume pumps have bigger (taller) gears so they move more oil per revolution. High pressure pumps use a stronger spring on the relief valve. You can combine both.

If you kept tight rod clearances with a high volume pump I could see these kinds of pressures being expected. But the gauge not returning to zero does of course indicate some kind of instrumentation issue to sort out first before worrying about the rest...

Good points Dave,

I think the high pressure is stretching the parts in the mechanical gauge that is not allowing it to return to zero. I could be wrong but I would really like the piece of mind knowing the true pressure, especially when cold. I have had oil filter seam leaks with high pressure as well as twisting oil pump drive shafts from the distributor.

[TBONE1964]

Originally Posted by davepl

I have a 60psi, is that the "normal" one? I knew there were 80s out there but am not sure what the standard unit is.

Yes Dave,

60 lb is normal and the 80 lb were used on the C-50/C-60 trucks with big blocks. Not sure if they were installed with a 1/2 ton 402 or not. Would be curious to know.