Burp system.
Ensure that the heater hoses are connected and not returned looped. Then burp the system. Previous owners who had trouble with heater cores have returned loop the system for bypass.
Memory is failing me at the moment... there should be a tower on the RHS of engine with a hex head nut similar the one found on the radiator. Whilst the engine cold. Top off radiator using the fill plug at radiator. Top off overflow to cold level. Remove hex nut at tower and run engine to operating temp with fan selector switch on high and full heat. Monitor overflow tank levels. When fluid reaches top of tower, replace hex nut. System should be fully bled. I typically purchase Prestone 50/50 for ease.
Have fun.
1990 RRC, 3.9L, AUTO "Willow Pond" (Sold)
1996 D1, 4.0L, AUTO "Lucas"
1999 RR, 4.0L, AUTO "Belle" (Sold)