99 Ford Explorer Leaking Antifreeze

I have a 99 Explorer that I thought had a small oil leak, however, after crawling under the car I identified it was antifreeze and not oil. It appears as though it is coming down the back of the block (looks like a oil seal leak). I have been noticing a little bit of an antifreeze smell lately but didn't think too much of it. My son (who drives the car) informed me that the heater has not been getting very warm and that when the car engine warms up the heat guage is going to the top and that the check guages light comes on. After about 30 seconds the light goes off and the temp guage drops. I am assuming that the thermastat is sticking but where would the antifreeze be coming from. There is no antifreeze present on the top of the engine, only on the cover plate between the engine and tranny. Thanks for any help you can give.

Freeze plugs? This is where my leak is coming from on a 2000 Ford Explorer. The a-hole that had it before me overheated it and damaged the plugs. I am using Bar's sealant to limit/stop the leak.

I like Metalic block seal protect, because it doesn't contaminate the coolant system.

Neither products will help, if you got a bad rubber heater hose, get a pressure test done ASAP to determind were the leak is.

We have used Metalic block seal with great success for bad freeze plugs.