Coolant Leak From Heater Core on GMC Sonoma

Problem Description and Possible Solution

The heater core under the right side of the dashboard may leak engine coolant which can puddle on the passenger front floor. The loss of coolant may cause an engine overheating condition. Our technicians tell us that removal of the dash board is necessary to replace the heater on these vehicles.

Problem Data
RepairPal Verified
Average mileage: 150,511 (78,000–200,000)
11 model years affected: 1991, 1992, 1993, 1994, more1995, 1996, 1997, 1998, 1999, 2000, 2001
25 people reported this problem
Viewing 1 - 10 of 10 comments
Replaced heater core - 5 hours and 100000 screws later the heater core is replaced and my fingers are bleeding engine coolant.
Fluid leaking from under dash
Pulled the dash half out
heater core leak in duct work spaying on windshield when blower engaged, leaking heater core replaced.
I have to check coolant daily. The windshield has a permanent foggy, moist appearance. I am waiting for the weekend to fix it. It's Wednesday today.
heater wasn't working so disconnected it for a while. after reconnected, leaked massive amounts of fluid (about 1/2" on passenger floor) so disconnected it again. need to pull dash and fix as it's winter and no heat is no fun.
No heat heater core not working correctly speed one and 2 is not blowing on the heater motor.
Coolant leaking on passenger side of cab
coolant leaked onto passenger side floorboard.. estimate was $350-400. had to take apart dashboard
Smoking from vents foggy windshield
loosing coolant in front of the firewall