Blown Head Gasket Cylinder 1 - Diagnosis and Replacement on 7MGTE

Engineadvanced✓ OP Confirmed

Problem

1989 Supra Turbo (103k miles) had cooling system issues: coolant would not fill properly and bubbled continuously in the overflow tank. Initially suspected radiator cap or hoses, but after a short drive the coolant smelled like exhaust, confirming combustion gases were entering the cooling system.

Coolant would not fill up completelyContinuous bubbling in overflow/expansion tankRadiator hose pressurized immediately on cold startHeater only blew warm air, not hotCoolant smelled like exhaust after drivingCoolant found sprayed over intercooler area from overflowEroded plastic at radiator cap seal preventing system from holding pressure

Root Cause

Blown head gasket on cylinder 1 (very minor breach barely visible on the gasket surface), allowing combustion gases into the cooling system. Additionally, the radiator had eroded plastic at the cap sealing surface, which prevented the cooling system from holding any pressure and masked the true severity of the BHG.

Confidence

Moderate confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted January 2021 on SupraForums.com