Yes it could be clogged. Check the heater hoses to be sure. One will be hot, one will be warm probably. If the core is ok, they will both be hot. If it's clogged, a radiator shop is the BEST betbut you can do it with a garden hose if you want. Just be careful, the core is NOT designed to handle the full line pressure that your garden hose and supply, you could rupture the core accidentally.