The 31 was the notorious pair of Volvo’s that ate me out of house and home with multiple cylinder failures, no support from Volvo and three separate rebuilds on two engines before getting rid of them. Yes, they smoke when cold. Personally I would not run them at all until you compare your serial numbers to the Volvo service bulletin regarding improvements to mfg process for oils cooling nozzles, though it is not in Volvo’s electronic record. paper only. If they have made it to 4K hours without multiple failures, almost certainly not in the impacted serial range, but if the seller did not include their history, think seriously about dumping them. Narrow range of engines with high failure rate and Volvo did not do a recall or assist. Bulletin was misleading at best.