The Vintage Sports Car Club of Australia

Temperature Warning Alert 

by Warwick Nicholson

 I’d like to describe a device that will forewarn drivers that their engines are approaching overheating temperatures. This problem was written about in last December’s VSCCA magazine, page 71, humorously caused perhaps by old timer’s (rhymes with Alzheimer’s) disease where a driver forgot vital adjustments causing his car’s cooling system to suffer some embarrassing incontinence.

 Not noticing an engine overheating could happen to anyone driving a vintage car as there’s more than enough to do in modern traffic using a crash gearbox, adjusting the spark, giving hand signals, leaving an adequate stopping distance without continuously looking at a water temperature gauge, if one is fitted, and particularly on a car that normally runs cool.

 Our car usually runs cool except on a very hot day, driving on a hot road pulling up a long grade at expressway speeds. Running hot may only happen once every few years so to monitor a temp gauge every couple of minutes when not in a hot situation seems pointless but could be dangerous. Even if you do check your temp gauge regularly there might be a major coolant leak, and subsequent overheating, between glances at your instruments.

 What we’ve done is fit a warning buzzer that only activates when the water temp approaches the critical zone. When it buzzes it reminds you to look at your temp gauge and gives you time to pull over, safely, for a check over or lets you know it’s time to back off the throttle till things cool down before the engine overheats.

 It was fairly easy to fit and does give you some peace of mind that something is continually monitoring a vital temperature which could help avoid an engine seizure. The main part is wiring in a heat activated switch. These are available at most motor accessory shops and normally used to engage a second electric radiator fan on cars fitted with air conditioning.

 This new switch can be powered from either your battery isolator, ignition switch or electric fuel pump then put in a circuit with a Dick Smith buzzer. The switch’s heat sensor is placed in a suitable water passage, ideally down low so it’s always immersed in your coolant (and will still work if your water level drops) or at a known engine hot point.

 You can easily set the temperature that these switches close, making a circuit, by placing the sensor in a saucepan of water then heating it to adjust the switch before fitting to your car. Perhaps to begin with pick a cooler temp for it to activate to satisfy yourself that it does work. To readjust the closing temperature you just turn a knob.

 We’ve added a ‘push for off’ button in the circuit to temporarily kill the annoying buzzer if it is activated. The driver, or navigator, just holds their finger on the spring loaded button, easily reached under the dash board, while working out what step to do next with the engine approaching overheating temperature. When the engine cools the buzzer stops.

 Now, you might ask, if your engine rarely overheats how do you know that your warning buzzer still works after years of inactivity? To regularly check our water temp buzzer we’ve wired it into a ‘low oil pressure warning system’ circuit. Every time the engine is cranked over before starting the one buzzer, which serves two purposes, is activated and so checked. Perhaps this low oil pressure safety system could be written up in another VSCCA article if anyone’s interested?