The second car, old coolant and a slow failure
Plenty of households here keep two cars, with one doing the station run and the school drop-offs and the other sitting for days at a time on a wide 1930s road near Auriol Park. The lightly used car is the one that catches people out. Coolant degrades by time rather than distance, and after a decade its corrosion inhibitors are spent, so the metal around the gasket's coolant ports pits quietly away. A car with barely any mileage on it can lose a gasket without ever having run hot.
The busier car has the opposite problem. Central Road is the only real through route and slows down with shop parking, bus stops and crossings, especially on Saturdays, and the North Cheam crossroads where Cheam Common Road meets the A24 is a busy signalised junction with supermarket traffic. School-run congestion fills the residential roads twice a day. All of that is low-speed, stop-start work where the cooling fan does everything and a radiator with clogged fins has nowhere to hide.
Either way, we test before we touch. A pressure test shows whether the system holds, a chemical test looks for combustion gas in the coolant, and compression and leak-down readings show whether neighbouring cylinders have lost their seal. We also check the oil cooler and, on an automatic, the gearbox cooler in the radiator, since both can mix fluids and look exactly like a gasket failure from the driver's seat. The written quote follows, not the other way round.
If you are weighing up whether to bother, we will give you the figures for the repair and for a good used or reconditioned engine, so the decision is yours and based on real numbers. The rebuild uses a full gasket set, new torque-to-yield bolts and coolant to specification, with the original cooling fault put right as part of the work. Collection and delivery can be arranged, and the workmanship carries a 3-month warranty.

