Drysump pressure drop
Drysump pressure drop
I am racing an EProduction mazda miata in SCCA club racing. As the stock miata oil pump regulator is proned to problems, I've "made the plunge" and switched over to drysump.
On startup, I have adequate pressure - about 40psi at 2K rpm idle. As RPM increases, so does oil pressure- up to 75 or so when the regulator kicks in.
Here's my issue: After startup, letting the car idle for say, 60-120 seconds, the pressure starts dropping... down to say 15psi where I get chicken and shut it off. The oil temp is maybe 100-110 at that point - way before anything is warm.
If I let the car sit for 30 minutes, and try again- voila my oil pressure is back to 40 ... but then the dreaded pressure drop starts all over again.
My system is the following: four-stage TDC pump, two -10 scavenge lines from the pan, one -10 scavenge line from the back of the head (in the valley with the valve train). The pump section for the head scavenging is much smaller than the two pan scavenge sections. Each of those lines is about 18" in length.
There's a -12 line heading back from the engine compartment to the trunk area; that line enters the top of the 24x6 tank. Another -12 line returns along side that line back to the pump.
The pump outputs into a -10 line, into a filter, into a cooler, and into the block at the stock oil filter input location. Just above that input is the stock pressure sender location, where I have my current gauge attached.
After speaking with several people, I believe one of several problems are possible - but I am looking for input / thoughts / whatever learning I can get.
1) The tank lines are too long, too far away from the pump, or simply the tank is too low relative to the pump for it to suck oil from the tank.
2) The head scavenge line is never below the oil level in the head. Specifically, it's basically in free air as far as I can tell. This seems like it's just sucking air into the system (minimal oil) and is asking more as a vacuum pump. Unfortunately for me another several cars have this setup but do not have my problem.
3) Some other problem I haven't thought of.
Diagnostics I've done so far:
1) Removed the line going to the tank, and verified that the pump is sending oil down the correct line. Simply turning the pump at starter speed shows the lines are hooked up correctly...
2)... however when the car is running, there really isn't that much fluid coming out. Yes with 20 seconds of cranking I can fill a 1-qt bottle, but the stream doesn't seem that consistent to me anyway.
3) When the pressure has dropped, I removed the valve cover and ran the starter again. You can clearly see a few air bubbles coming out the oil galleys for the lifters. It's not foam by any stretch, but there are bubbles for certain.
Any and all direction is appreciated. Thanks for your time.