Low oil pressure reading

[blaze65]

Have been working on getting my 200 going. This is a rebuild that was done about 18 months ago and has just made it into the car. Car is running but the oil gauge is showing a very reading. Might be a bad gauge as the needle has a starting point is below the 'L' on the gauge. It does move but barely gets to the first '|' line on the gauge. which is what I would expect to be the normal starting point for the needle. 200 is bored about .30 over with new 260H cam. Oil sending unit is also new although I am not using the extension on the oil sending unit. I also don't have anything hooked to the PCV valve or the valve cover breather at present. I don't think these not being connected however impact true oil pressure. Car is not actually on the road and have been starting it just in the driveway. Car starts right up and sounds OK, although it does seem to have what sounds like a small valve tap. (Not sure i should have that in a fresh build)

I plan on picking up a pressure gauge and attach it directly to the block to see what the real reading is. Questions I have though are

what should the PSI be for a 200 ?
what type of oil should I be using ?
Is a valve tap after a rebuild abnormal ? or are adjustments after a rebuild common ?
Are the disconnected PCV and Air Breather having any impact on the oil pressure ?

Many thanks

Bill

 

[rbohm]

i assume that this is an electric gauge, so first make sure that you have clean threads where the oil pressure sending unit screws into the block. it is pipe thread so you really dont need sealer which creates a ground issue.

second if this is the factory gauge, make sure the connections to the gauge and sending unit are clean and tight. then test the gauge. with the key on, engine off, ground the sending unit wire and if the gauge shows a reading at the top of the scale, then the gauge is good to go.

third, you may need to drop the oil pan to check the oil pump. make sure the pressure relief is not stuck open, and make sure the oil pump drive shaft if in it proper place and not twisted up. also check that the oil pump pick up is on tightly and not drawing any air, and that the screen is not clogged, and has 3/8" clearance with the bottom of the pan. that should get you started.

 

[blaze65]

Many thanks. Will test all of that and repost with my results.

Bill

 

[rbohm]

the other thing you can do to test things easily is to install, temporarily, a mechanical oil pressure gauge and see if you really do have a low pressure situation, or a gauge situation. that way you know for sure one way or the other which problem you really have.

 

[blaze65]

Tested again tonight with some different results. First thing I did was ground the Oil Sending unit with the Key on. Needle pegged so that seems to say the gauge is good. They I remove the teflon tape for the threads of the oil sending unit. (thank you for that suggestion). Tested again and the needle did move a little more although it still signals low.

With the key off the needle on the gauge has a starting point below/behind the letter L on the gauge. When running the needle moves from behind the L, past it, and up the the very first line on the gauge. If this first line on the gauge were the starting point for the needle I imagine the movement would put the needle somewhere in the middle of the gauge.

I will get a pressure gauge and attach it directly to the block. (Question is that 1/8 pipe thread ? ) . Gauges are 50 years old but do the gauges have any type of adjustment to reset the starting point of that needle ?

Thanks

Bill

 

[rbohm]

it sounds like you have cured the problem. at idle the gauge should read on the first line above teh zero point, and should go about 1/3 to1/2 the way up the gauge when running down the road.