My bracket car, with two different motors with different dual line Milidon oiling systems hasn't had any pressure problems when sitting for months at a time in the car trailer during the winters here, it has got down to-25F two years ago. I have ran 5w20Wt oil and 10x30 VR1 oil in the car since day one of me racing it 6 yrs. ago
I think I had more issues with straight 50Wt and later with 20W50Wt oil loosing the prime, even with Kendall GT1 20x50Wt oil