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Heater core in 2001 Ford Ranger

My husband is the original owner of a 2001 Ford Ranger with 160K miles and he’s never had any serious repair issues with it until two years ago. Since 2010, the heater core has been replaced twice due to leaking (new heater core, thermostat, o-ring and radiator cap). Then he noticed a couple of months ago that it is leaking again for the third time! As a temporary fix, he connected the water pump hoses together to bypass the heater core to stop the windshield from fogging but we need to get it repaired again before winter. We are really baffled as to why we would need three new heater cores in two years and we wonder if anyone else has ever had this problem. Your advice and input would be greatly appreciated!

Ford has issued Technical Service Bulletin 06-21-19 that addresses replacement of the heater core for repeated leakage. The leakage is a result of electrolysis that can occur in the heater core from either worn out coolant or a poor engine ground.

To test the coolant, remove both battery cables from the battery and make sure they don’t touch each other or any part of the vehicle. Using a volt/ohm meter, connect the black lead of the meter to a known good gound and insert the tip of the positive lead into the coolant. Check for both AC and DC voltage. The voltage reading should not excede .4 volts AC/DC. If the voltage reads over .4 volts AC/DC replace the coolant.

To check for a poor ground, reinstall the battery cables. Turn the ignition on but do not start the engine. Using the meter, check for AC/DC voltage at all engine ground connections. If a reading higher than .4 volts AC/DC is found at any ground connection, remove the ground connection, clean the ground connection and reinstall the ground connection.

Here’s the TSB


That surely does sound good to me… Interesting and certainly possible

Thank you Tester!