I need some help from the experts. Some background, I am running a brand new bridgeport 4 port motor in my sorta like a WC RX7. I like to think that if the WC still allowed 1991 RX7's in the series, my car would be the type. I run mid-pack WC times. We are running a Turbo II oil pump with an FD regulator and Aeroquip #10 lines. Valvoline 20 - 50 Racing Dino oil until we finish break-in. The oil cooler is a brand new stock Mazda FC cooler with the thermostat removed by the Mazda dealer. It was run in my previous engine and never really showed any issues other than a sleepy gauge (slow to react when cold). The oil pressure gauge is plumbed using the stock pressure pick-up point. We ran a different cooler before (a Long style) and the pressures were better but the temps were higher.

Now the issue. When the oil is hot the car runs 60-70 psi at idle and 110 at 2500 rpm and the car never has oil temps above 200 F (just ran a 3 Hour enduro yesterday and the car was making these rates after the race as well). When I start from cold the oil pressure takes about 10 seconds to read above 15 lbs and slowly crawls up as the oil temps go up. Once the oil temps reach 140 no issues.

The second tell tale is that if you start the engine from cold then shut it off right away (5 - 10 seconds), then you check the oil it has tons of little bubbles in it. The bubbles go away after you let the oil sit for 5 minutes or there are none if the oil is hot.

My crew chief and I have 2 theories. First, the oil is very thick and is cavitating as it passes through the cooler when cool and as it warms the viscosity drops and it flows more freely reducing the cavitation. Or secondly the cooler is very restrictive and the cavitation happens in the oil pump as it tries to force the oil through the cooler and is unable to.

We believe it is the cooler as the cause, but what is the cure, should we re-install the thermostat into the cooler to allow free flow of oil when cold? I don't understand why this is a problem with the new Mazda cooler when cold and not the ancient corroded oil cooler I had on the car previously?

Eric