Coolant Leak From Heater Core on GMC Sonoma

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.

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Average mileage: 148,062 (78,000–200,000)
10 model years affected: 1991, 1992, 1993, 1994, more1995, 1996, 1997, 1998, 1999, 2001
22 people reported this problem
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Viewing 1 - 9 of 9 problem details
Replaced heater core - 5 hours and 100000 screws later the heater core is replaced and my fingers are bleeding engine coolant.
1992 GMC Sonoma 160,000 mi,
Fluid leaking from under dash Pulled the dash half out
1996 GMC Sonoma 148,000 mi,
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.
1991 GMC Sonoma 180,000 mi,
loosing coolant in front of the firewall
1996 GMC Sonoma 200,000 mi,
No heat heater core not working correctly speed one and 2 is not blowing on the heater motor.
1995 GMC Sonoma 124,567 mi,
Coolant leaking on passenger side of cab
1998 GMC Sonoma 78,000 mi,
heater core leak in duct work spaying on windshield when blower engaged, leaking heater core replaced.
coolant leaked onto passenger side floorboard.. estimate was $350-400. had to take apart dashboard
1991 GMC Sonoma 155,000 mi,
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.