Originally Posted by Chargerfan68
Originally Posted by AndyF


The oil pressure doesn't change, but the reading on the gauge does. The oil pump is still pushing the same amount of oil thru the bearings. The oil pressure gauge is "recalibrated" by the vacuum pump. Instead of reading from 0 to 100 it is now reading from -10 to 90.


I can understand that the oil pressure does not change. The gauge reading change I am having a little trouble understanding. Can you or anyone explain why? The way I am thinking about it, it the oil passages are full of pressurized oil and the oil sending unit is at the end of that passage, if the pressure itself doesn’t change, how would the reading change? I inderstand the unit is referenced off atmospheric pressure externally

Thx for all the replies.


If you really want to know what is happening then you need to reference the oil pressure gauge to the crankcase. There will be a small port on the back of the pressure gauge that is open to the air. You need to solder a small fitting on there and then use a piece of vacuum hose to hook that port up to the valve cover. Once you do that you'll be able to read the actual oil pressure inside the engine relative to the crankcase.