Has it always done this? How many miles on it that way? Standard or HV oil pump? (the std one is about 1.25" thick from the block flange to the top casting, the HV isa about 1.5" thick there) You should get yourself a gage (preferably a decent one..not the cheapo 2" ones) to see what it really is doing. Could be nothing. Could be serious. If it's a HV and it has that issue, that's bad. If it's a std pump, at idle, it's not bypassing due to pressure, so upgrading the bypass spring wont help. You could just install a new HV pump if it's standard, but that may not do much more than mask the problem. A good oil gage will tell you what the pressure is at idle. Thicker oil may also help if you're running 10W oils.