thermostat?
 

my friend has an 88 FC and he kept losing coolant. where it was goin, we had no idea and the car would almost over heat. so i was checkin it out one day, and i realized the resevior was about 2 inchs more then i noticed last time. is it possable the thermostat isnt opening properly and that the coolant is boiling over, making the excess coolant go into the resevior? is there anything else that could cause this?

remove the thermostat, place in a pot of room temp water along with a cooking thermostat. start heating the water. Once the cooking thermostat reaches 185 or 190 degrees F. Check the thermostat and see if it's open. If it is not open at that point then it is defective, get a new one. Autozone charges like $12 for them. Make sure you get a thermostat that operates at the same temp, they sell a 196 degree thermostat too, but you want the OEM equivalent. (It is easier and faster to check the thermostat than it is to post your question here and wait for a reply)

you would want to avoid any non OEM thermostat or the car will run warm or have other issues.

And your problem sounds more like a leaking pressure cap than a bad thermostat.

yeah u need a radiator cap and a t-stat

I sell both JAPAN made oem items. hit me up if interested in a price

mines leaking at the filler cap everytime i make long distance trips. so i replaced it with a new cap and it still leaks. what pressure cap would you guys recommend?

0.9bar is the coorect pressure. That's not why it's leaking. If it's a new cap then there's probably something wrong with the neck it screws onto.

checked that also and it seemed to be in perfect condition.