Step-by-Step Guide to 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.

Performing a heater core bypass will leave you without heat, so you’ll have to make other arrangements for heat. See other options below.

How to install a bypass hose

Tools and supplies needed to bypass a heater core

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

This is what the heater core bypass should look like when you’re done.

Refill the cooling system and burp air pockets

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

Use a handheld vacuum pump to remove air from the cooling system.

To get heat, install an aftermarket underdash heater to warm the cabin

When you’re done installing the U-shaped hose, you’ll have to make other arrangements to get 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.

Aftermarket units mount under the dash and have a blower and heat exhanger. To install, run the heater hoses to the unit and connect to power for the blower.

Aftermarket heater devices that mount under the dash. Run the heater hoses to the units and connect to power

©, 2018 Rick Muscoplat