Heater works just fine, blowing nice hot air, but as soon as I turn it on, the engine temperature gauge soars and quickly shows an overheating engine. Is this a major repair?
May or may not be a major repair depending on what the issue is. Allowing air to flow through the heater core should do the opposite and remove heat from the system. I would bring it in to have it looked at ASAP before more damage occurs due to overheating. At that point it will be a huge repair. Good luck.
does it drop back down when you turn the heat off ? sounds like faulty wiring I wouldn't think the temp could rise like that for real
You might also be low on coolant, this vehicle has a heater control valve that opens to let coolant flow to the heater core, it can cause a drop in coolant flow. That drop in coolant flow causes the engine to start running hotter. Check coolant level and top off. This is a pretty old car too, might want to check every part of cooling system, especially radiator, for good flow.
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