Cooling system Introduction

There seems to be a number of people who have had costly repairs carried out, only to find out some time later, that the same overheating problem has returned to haunt them. So what's going on?

Toyota are renowned world wide for producing good quality cars. This is not by accident, its by design. My opinion is that the cooling system on Toyota's Ace family, is a finely balanced, albeit quirky system, that can seem to overheat for no apparent reason.

So what makes it different?

Most cars will start to overheat in stationary or heavy traffic, and will quickly cool down once moving forward at a reasonable rate. The Townace is designed to be capable of sitting in stationary traffic most of the day if necessary. It only starts to struggle when the engine is under high load. For example, towing big loads, going up steep hills, motorway speeds, and off road driving sap quite a lot of power from the engine. Add any of these conditions together, and turn on the air conditioning on a hot day, and not surprisingly, the Ace family start to get a bit warm. Stop the car, keep the engine revs at about 1200, and watch the temperature gauge fall.

What makes it quirky?

The automatic and 4 wheel drive versions have a second cooling radiator, mounted horizontally under the air conditioning radiators, which are also mounted horizontally, under the front floor pan.

There is very little, almost no natural air flow through the radiators.

The thermostat is mounted on the cool return radiator hose, at the bottom of the engine block. In order that this can work effectively, there is a metal receiving bracket mounted in the thermostat housing on the engine block. This acts like a heat sink to the engine, and prevents the thermostat from closing as soon as it opens when the cool coolant is drawn in. In essence, whilst the thermostat opens according to the temperature of the coolant, it closes according to the temperature of the engine block.

Dave Bright, 25 Sep 2003.