Jim Grant's Tech Tips
'93 GMC Sonoma, Coolant in the Cab
Q: Antifreeze is leaking inside the cab of my 93 GMC Sonoma. What could this mean? It just started and I've never had this type of problem before in any vehicle I've owned.
A: You have one of two problems. Either the heater core is leaking or the hose clamp on the heater core fitting is loose. Weve seen loose hose clamps allow coolant go right into the heater box and run out like there was a failed heater core. If the clamps are tight and no leaks are found where they connect to the heater core then a replacement heater core is likely needed.