What's the service history of the cooling system? Has the coolant been replaced/flushed regularly? If not, there is a chance that the old radiator is gummed-up inside. It happened to me, but mine fell victim to a head gasket leak...

Does the car blow hot air when the heater is on?

-GH

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1992 Mercedes Benz 500SL
1998 BMW 528i
2003 Honda Element
2002 CBR600F4i
1977 Coachmen Motor Home