Heater core bypass

How to perform a heater core bypass

A leaking heater core can cost upwards of $1,500 to replace. It’s a huge job that requires removing the entire dash to get to the heater box where the heater core is mounted. Due to the high cost, many owners opt for a heater core bypass procedure, which, as the name implies, bypasses the heater core.

How to install a bypass hose

Tools required:

Hacksaw, cut-off tool or reciprocating saw with metal blade
File
Flaring tool

Supplies needed

Bypass hose
Hose clamps to match the diameter of the heater core bypass hose

Choose a heater core bypass hose to fit your vehicle

Drain the cooling system before disconnecting heater core hoses from the firewall

Drain about a gallon of coolant from the radiator.

Cut the heater hoses near the firewall

Use a utility knife to cut rubber heater hoses or a tubing cutter to cut steel heater lines. If your lines are steel or copper, use a file to clean up the edges.

Install the heater core bypass hose

Lubricate the inside of the heater hose with coolant. Then slide the bypass hose or fitting into the heater hoses and tighten the clamps

image showing heater bypass hose installed

Refill the cooling system and burp air pockets

Follow shop manual procedures to remove air from the cooling system. Or, use a hand operated vacuum pump to pull a vacuum on the entire cooling system to remove air.

Mityvac MV8000 Automotive Test and Bleeding Kit

Install an underdash heater to warm the cabin

Bypassing the in-dash heater core means you won’t get any heat. If you run the defrost, you might get some residual coolant spray onto the windshield. But if you need heat, you’ll have to install an underdash heater.

©, 2018 Rick Muscoplat