I had been fighting a heat soak / vapor locking issue with my 71 olds. She would run great and get up to a good operating temperature and be fine. Until, I let her sit for about a half hour after and wouldn't want to start and if she did she'd want to die until she got cooled. I was pulling my hair out! I read about the phenolic spacer on classicoldsmobile.com and figured I'd give it a try. WOW! Night and day. I installed this and changed to a 160 thermostat and haven't had a problem since.