General repair Q's about my 92' Plymouth Voyager mini-van?

92' Ply Voyager mini van 3.0 V-6 fwd. I just got this thing for $300 as a 2nd vehicle. I'm not a mini-van guy and this thing is SO unlike me , and that's what's kinda cool about it, LoL! It's ugly , rusty, and chipping paint! The interior is surprisingly good though. If i drive into town , i need to feed it a qt of oil - in fact it takes 1 qt a day , ..running or not , LoL! Seller included a new set of valve cover gaskets and said that was the reason for oil leak , ..and i can see that THAT is true. What about this though? Temp gauge hardly moves unless idling , when i drive it goes to zero. What's that mean? No thermostat? Stuck thermostat? No coolant loss, but coolant appears dirty so i will change that. Doesn't appear to be oil residue in coolant. Oil cap DOES reveal a small amount of milky "something" under it , but wiped it and hasn't reappeared - again , no coolant loss , so i'm not sure if i'm looking 100% at a head gasket issue. Motor seems to run smooth , i know it could use a tune up. Doesn't smoke much unless it sets up for a period of time , such as when i first tested it at the owners house , and it was light blue smoke not white - hasn't hardly done that since i start / drive it everyday. So you mechanic types , what's your take on my van? I'm kinda concerned about that white stuff under the oil cap - but if i have a head gasket issue , i'll simply pour in some CRC or other liquid "fix". I'm not about to sink loads of money into this thing!