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Q: Went to flush radiator, car heated up and refused to turn off

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I replaced the water pump yesterday and went to flush the cooling system today, I filled with flush and water, put cap on and started engine, my car heated up quickly and refused to shut off, I had to hit the stop lever on the engine to turn off... did I mess up somewhere?

My car has 300000 miles.
My car has an automatic transmission.

There is a vacuum pump on the front of the engine near the water pump, The large vacuum line that comes out of it branches off to three or four smaller lines not far from the pump connection. They are made of plastic and become very brittle over time. You probably disturbed one or more of these vacuum connections while you were working at the front of the engine. The shutoff valve is vacuum operated so any leaks will leave you unable to shut off. Also, I recommend you leave the radiator cap off while running the flush. The system is going to "burp" a few times and need topping off. Likewise, leave the cap off during the warmup so you can continue to top the system up. If you have trouble sorting out this shutoff valve, or if you continue to have cooling system problems, Your Mechanic can send a technician to your home to sort out the vacuum leak for you.

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