Having had to fork out just over a grand to get a replacement engine fitted because of the dreaded overheat problem, I am driving with one eye permanently fixed on the temperature gauge. What I was wondering was, to save me from going boss-eyed, is it possible to fit an audible warning for when the head temperature/water temperature reaches a (nearly)/ critical point? Would be more useful than the Japanese Finger Bells!

Tom

- (#6763) Tom Lister, 15 Jan 03

yes tom it is, in fact unless im mistaken dave milller has done just that

jim

- (#6764) J ADGO, 15 Jan 03

not audible, but a couple of warning lights... One comes on at 100c along with the 'lekky fan, the other at 105c

- (#6765) david miller, 15 Jan 03

Last summer I was developing just such a device to sound when the voltage across the temperature gauge sender drops below a chosen level (around 4V). I wanted a design that other owners (whether with Toyota or Durite gauge) could easily fit and adjust the threshold to suit them - which requires some self-test feature to simulate raised temperature. It's an extension of what I wrote up as "Temperature Gauge Investigation".
Believe it or not domestic politics turned that exercise into developing a workshop in the loft. Fortunately that's nearly finished so I'll then get back on the job! Email me if you want to discuss the circuit design issues.

- (#6846) Dave Mason, 17 Jan 03

I have made some good progress with an audible warning warning and intend to get someone else to try it out very soon. I've realised that at the same time as providing an overheat warning this easily-fitted gadget could drastically improve the response of the gauge (better than just adding the Ace Answers 47ohms modification).

By wiring on (same place as the 47ohms) this alarm unit, the Toyota gauge would then read reasonably smoothly across the whole dial, say, from 70degC to 110degC. To know whether this is in practice the useful range I would be interested to know from a few of you who have fitted a Durite gauge ...

1. What is the top temperature ever indicated, barring disasters? (and for the really keen, what is the voltage on the sender then, i.e. the trip level for a Durite version of my alarm, should there be any demand for one?)

2. What is the lowest indicated running temperature - cold night, gentle cruise?

There will be no definitive answers to these so I would appreciate several responses. Thanks.

- (#7178) Dave Mason, 14 Feb 03

Dave,
I swap my thermostat for summer or winter. Currently, with the "float" type Toyota thermostat fitted, modified with one 3mm "bypass hole in the flange, the maximum temperature indicated is 95c (Durite gauge). This is motorway journeys, hilly A roads, around town etc. On the "cold night, gentle cruise" type of journey, after initial warm up the temperature seems to hover around 80/85c. My summer thermostat has three x 3mm bypass holes and the top temperature indicated(Scottish hills in the summer) was around 95/100c.
I am not sure whether the themostat type/modification etc is going to be a factor in your calculations. I know that when I ran, for a short while, with an unmodified Toyota float type stat, the temperature seemed to get too near the 100c mark for my liking so, perhaps, your max "switching" temperature might have to be aimed at just over 100c for all those systems which run with unmodified thermostats.

- (#7260) John Davis, 15 Feb 03