Originally Posted by Farnsworth
Part of the problem is talking about hot flow, then talking about sub zero maple syrup oil. I learned something about oil pump relief valves. I thought they were much higher psi. In freezing conditions, with a too small bypass valve area, the bypass say is one of those high 30 psi, what happens to the wall of maple syrup hitting the oil filter? It immediately has high back pressure. So if the dp is 30 psi at the filter, it needs more than a 60 psi oil pump valve, or the flow will be kept to the 30 psi. Maybe 30 is OK, but it seems low. The thick oil will take longer to get through the passages.
I think most vehicles have more like 70~80 PSI relief valves ... some over 100 PSI. But in any case, if there actually was 30 PSI of delta-p across the filter due to very cold thick oil, then yeah the pump outlet would probably hit the relief pressure setting. If the delta-p across the filter was way less in those conditions then the pump may not hit pressure relief unless the engine is revved up some before warm-up. 30~40+ PSI of oil pressure on the downstream side of the oil filter at start-up is most likely adequate. Again, more reasons to not rev the engine much until the oil warms up some.
Originally Posted by Farnsworth
When I had a small motorhome Chev chassis back n the day, I remember hot oil pressure say about 50 psi cruising along at 3000 rpm. Then when a hill is climbed the engine goes much higher probably to 5000 and I remember the oil pressure going considerably higher, maybe 70. Then coming back down after the engine returns to cruise. Many factors affect the oil gauge.
Sounds like normal Chevy 10 PSI per 1000 RPM behavior ... all totally normal, that's how oil pressure works with a PD oil pump.
Part of the problem is talking about hot flow, then talking about sub zero maple syrup oil. I learned something about oil pump relief valves. I thought they were much higher psi. In freezing conditions, with a too small bypass valve area, the bypass say is one of those high 30 psi, what happens to the wall of maple syrup hitting the oil filter? It immediately has high back pressure. So if the dp is 30 psi at the filter, it needs more than a 60 psi oil pump valve, or the flow will be kept to the 30 psi. Maybe 30 is OK, but it seems low. The thick oil will take longer to get through the passages.
I think most vehicles have more like 70~80 PSI relief valves ... some over 100 PSI. But in any case, if there actually was 30 PSI of delta-p across the filter due to very cold thick oil, then yeah the pump outlet would probably hit the relief pressure setting. If the delta-p across the filter was way less in those conditions then the pump may not hit pressure relief unless the engine is revved up some before warm-up. 30~40+ PSI of oil pressure on the downstream side of the oil filter at start-up is most likely adequate. Again, more reasons to not rev the engine much until the oil warms up some.
Originally Posted by Farnsworth
When I had a small motorhome Chev chassis back n the day, I remember hot oil pressure say about 50 psi cruising along at 3000 rpm. Then when a hill is climbed the engine goes much higher probably to 5000 and I remember the oil pressure going considerably higher, maybe 70. Then coming back down after the engine returns to cruise. Many factors affect the oil gauge.
Sounds like normal Chevy 10 PSI per 1000 RPM behavior ... all totally normal, that's how oil pressure works with a PD oil pump.
