Low Oil Pressure

[Tommy]

Oil Pressure Drop

When I fire up my 6.3 V8 the oil pressure on the gauge is good but once the engine is up to normal it drops,
according to the gauge, to 25lb and after a run, the gauge shows it at about 15lb on tickover.

The engine is not making any odd noises and seems OK but I obviously do not want to do any
avoidable damage. I assume the temperature of the engine is irrelevant so far as the reading
on the gauge is concerned, so should I change the big end shells? Or should I start with a
new oil pump?

Advice welcome please

[cannonball]

First thing get hold of a mechanical oil gauge capillary not electric, and see what honest oil pressure it really has, if its still grim then pull the pan and see what state the bearings etc are in and go from there, that is assuming you have a new oil filter and oil has been changed very recently,,

[slotcarone]

Oil pressure is typically going to show higher on the gauge when the engine is cold and will drop when hot. What is the condition of your engine? Has it ever been rebuilt and how many miles does it have on it? Is it clean inside or sludgy? If it is not using oil and sounds fine probably nothing to worry about. Don't forget these engines when used in their original cars rarely if ever had an oil pressure gauge. Only a low pressure light. Also have you had this car for a long time and did the oil pressure used to be higher/different and now it is low? Really need this info to advise correctly.

[kenny38]

Hi, My oil pressure was low and got lower when hot. Mechanic said it was oil sender. Changed and never goes below 45-50. He also said that unless warning light comes on don't worry as these engines'oil can go down to 5. No light....no worry then........but there again......Kenny38

[slotcarone]

That's great Kenny!! Drive on!!

[Chris_R]

Oil pressure will always drop when hot as the oil thins. The temperature is not irrelevant, the hotter the engine, and the hotter the bearings in the engine, the lower will be the pressure as the oil thins more with more heat. The pressure you are seeing is the resistance given mainly by the bearings on the crankshaft to the flow of oil through the engine from the pump. A thicker oil would give a high resistance to flow and thus show a higher pressure reading, a very thin oil would flow very easily and thus show a lower pressure reading. Most important is the flow of oil of the right thickness (or thinness depending on your point of view) at the right temperature to the bearings. It is not the pressure delivered by the pump that supports the bearings as the engine turns but a good flow of oil into the bearing space that gets dragged and compressed in the internal gap between the journals and the bearings that then supports the crankshaft.
Duncans advice is good. Get a mechanical gauge and cross check your readings. If it is verified to be low and you are concernced, possibly an easier route than pulling the pan and checking the bearings is to replace the oil pump and see if that makes any difference. If the pump is worn it might not be delivering as much oil as is needed to get a higher pressure reading. If replacing the pump makes no difference then your next step would be to check the condition of the bearings. You can check the clearances with some Plastigauge and that will tell you how worn they are.