I have a cansiter type block heater on our 1989 Suburban, which I bought at Walmart several years ago, but Walmart doesn't sell them anymore. It has always worked great. It doesn't have a pump, the heat just circulates the coolant. I went to NAPA and they have a canister type with a pump, which sounds like it would be even better, for $45. They also have a freeze plug type for $35. I know GM has a factory option, but my 1999 Silverado doesn't have that option. Does anyone have the NAPA canister type and if so, how good is it?