My Father in Law is looking at buying a used 06 F150 with 62K Supercrew XLT. Looks in pretty good condition, still rides solid, but there was something in the coolant overflow that looked suspicious to me. I wouls compare it to algae that was growing in a stagnate body of water. I know GM has a special coolant that if you mix it with the old stuff will congeal but I did not know if ford had that as well. Any ideas? and anything else I should look at other than having the dealer change the plugs before he takes delivery.

Thanks for the info in advance