I run crossovers on my new engines. I have 150* T-stats in place, and we drilled four 1/8" holes around the perimeter. Temps are perfect and steady. It allows for water circulation through the block at all times including during cold-start and idle to avoid hot-spots and air pockets. It also alleviates the situation where often times when running crossovers with bypasses, the t-stat won't open up due to the raw water dumping on top of the t-stat via the bypass which artificially keeps it cool. It takes a little longer to get up to temp, but I can maintain 150* right on the money.