Is there a shut off valve on a 1996 Cadillac STS to stop hot water flowing to the heater?

Answer 1

Most newer cars do NOT HAVE A HEATER SHUT-OFF VALVE. The water continually flows into the heater core inside the passenger cabin and is regulated by a series of 'doors' that direct the air-flow over either the evap. core (for A/C) or the heater core for heat.

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A broken or leaking heater core is a mess and very expensive to replace. The whole dash has to come out: glove box, dash pad, cigarette lighter, ashtray, all of that lousy fake walnut trim, etc. It takes almost 8 hours just for the 'teardown' to get to the faulty heater core that is probably leaking fluid onto the floorboard on the passenger side. Plus, since all of that crap is PLASTIC with little lock-down tabs, you WILL break a great many and there is not a glue made on the face of the earth that will repair automotive plastic. (That's how they make MONEY.) So, get a bunch of Velcro, a whole roll - you'll need it all if you begin to attempt this repair.

At $95 per hour at a dealership, the 'teardown' cost is $760. Expect to pay around $1,800 for a heater core. If you have an independent shop have at it - INSIST ON A GENUINE FACTORY PART. (I once had them use an aftermarket heater core and it failed three months later, so I got hosed for a very large sum of money, since the original guy that did the work was two states away.)

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There are two cheap fixes: 1) go buy a VISE-GRIP pliers and clamp down the hose leading from the engine to the heater core, try to find ones with FLAT surfaces on the pliers. 2) Cut the line (from the engine to the heater core and install a manual heater shut-off valve that will prevent the flow of coolant. Check out a bone yard, but MEASURE how big your heater hoses are FIRST, since different cars have different sixes of hoses.