When installing water temperature sensors of a Formula Mazda there are two common locations for the temperature sensor installation. This document compares these two placements, being the engine block and the swirl pot. Note that these are in addition to the water pressure sensor, covered separately. In the figure below, the cooling system is shown: temperature sensors have been placed in the engine block (Tb) and the Swirl Pot (Tsp).
When the engine is started, the 185F/82C thermostat is generally closed. As shown in the following figure, the water temperature measured in the block (blue trace) will start to rise immediately from ambient temperature, either cold, or, after cool-down from prior session as shown here. Also shown (red trace) is the ambient air temp (about 100F/40C) prior to coolant in the swirl pot and radiators warming up.
As the engine warms and reaches the opening temperature for the thermostat, cooling system circulation begins: this continues until the engine reaches its optimum operating temperature or 185F/82C, at which point the thermostat regulates the water temperature by controlling flow through the cooling system. Looking at the final figure below, the operating temperature is clear.
It’s clear that the water temperature as measured in the block and the swirl poot can vary, especially when running cooler ambient temperatures. Therefore the recommended primary water temperature sensor should be located in the engine block.
In addition to the block temperature, measuring the swirl pot water temperature and system water pressure can be useful: the swirl pot temperature profile will give an indication of the cooling system effectiveness: if the water continues to climb past the thermostat-regulated optimum temperature then the cooling system should be checked for blockage (both air fins and water). As well, air circulation should be reviewed as this is an indication that the cooling system is not able to keep up with cooling demand of the motor. And finally, by monitoring water pressure, leaks can be spotted. It’s quite possible for the system to drain itself of coolant, yet still show 180-210F (80-100C) temperatures. How? Because the sensors are measuring air temp in the now-empty cooling system! To catch this condition, a water pressure sensor can be fitted: if the pressure drops, a leak has likely developed; Setting an alert for low-pressure can help avoid otherwise costly engine damage in the event of coolant loss.
Understanding the operation of the Formula Mazda cooling system is essential to proper fitting of sensors and the interpretation of the data. Recommended temperature sensor placement is in the block with a 200F/95C alarm. A water pressure sensor, with an alarm set if pressure drops, along with a swirl pot sensor can be installed to monitor overall system performance.