7MGE Coolant Leak and Overheating at Idle with AC - Pinhole in IACV Coolant Hose

Coolingintermediate✓ OP Confirmed

Problem

7MGE NA MA70 Supra overheated while idling in a drive-through with AC running. Temperature gauge climbed to 3/5 of the way toward H. A coolant leak was present on the intake side of the engine but the source was difficult to locate visually. The car had been losing approximately 1/4 cup of coolant per tank of fuel for some time, with coolant residue visible on the subframe near the steering rack.

Temperature gauge rising above normal halfway mark when idling with AC onCoolant leak on intake side of engine with no obvious visible sourceHissing sound and coolant visible on block during overheating eventSlow coolant loss over time (~1/4 cup per tank of fuel)Coolant residue on subframe near steering rackNo overheating issues at highway speed, only when stationary

Root Cause

A pin-sized hole in the small coolant hose running to the Idle Air Control Valve (IACV) closest to the alternator on the intake side of the engine. The hole was too small to leave obvious residue or be found visually, but was revealed under pressure testing. The missing fan shroud also contributed to poor cooling at idle, especially with AC on, since the clutch fan was blowing air in all directions rather than pulling it through the radiator.

Confidence

High confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted November 2021 on SupraForums.com