I thought this topic earned its own thread as there is nothing on the forums regarding digital engine temperature monitoring. My experience reveals some interesting facts in relation to Magna/Verada cooling.

As some of you would have read, my Ralliart overheated on a 41 degree day. I subsequently found the thermostat to be only opening slightly and the radiator ended up having a fair amount of deposits towards the bottom. I have now replaced the thermostat and the radiator and cured the overheating issue. When I first purchased the car, the coolant looked green but when I first flushed the system there was a fair amount of rusty material released from the block. It clearly had missed some maintenance.

I have subsequently installed an Engine Watchdog to better monitor engine temperatures. This consists of a thermocouple fashioned as a washer that bolts under an engine bolt. The signal is transmitted to a digital display in the car. The device can be set to alarm both visually and with an unpleasant audible alarm when the engine reaches a set temperature. The company recommends installing under a thermostat housing bolt, but as Erad (who recommended the device) found, this was not that close to an engine head or the block. I installed the sensor under one of the intake manifold bolts, on the driver's side. This places it only 20mm from the rear head and away from exhaust headers. I have run the cable through the driver's side wheel well grommet and found this to be straightforward.

My experience so far.

The temperature reads 46 degrees when the gauge reaches its normal position (just under half).

In my car, on a mild day (say 30 degrees), the temperature only reaches 80 degrees after about 10-20 km of normal city or highway driving (no steep hills or towing).

The device reads 85 degrees when the thermostat starts to open (bottom hose getting hot). I did think it was closer to 87 degrees on a previous thread. The thermostat is an 88 degree unit and has been tested in hot water to verify it behaves as designed. So based on this, the head is a few degrees cooler than the coolant (at least where the washer is located). This is pretty close.

So with basically a new cooling system (my water pump was taken off and inspected recently at a timing belt change), the Magna doesn't seem to reach the thermostat opening temperature until ambient temps in the low 30s or very hard driving. This does go against the ideal operating temp of 90-100 degrees for modern engines.

I have tested the system on a 35 degree day by revving the car at 3000rpm whilst stationary (someone that never happens) and had the thermocouple go to 105 degrees. This was with the washer in the original location on a timing cover bolt near front exhaust headers. The temperature needle just started to move. I suspect the actual head temp was lower.

SO: the cluster temp gauge reads at normal operating temperature (just under half) from 46 to possibly a little over 100 degrees C. This is probably designed to give drivers some peace of mind and less distraction?

When the thermostat does open, the temps start to fall within 30 seconds or so.

Conclusion

Excellent way of preventing a cooked engine. If your water pump dies, you burst a hose, have a thermostat stick etc, the device will let you know much faster than the gauge. The gauge only reads coolant temps so if you dump your coolant, the device will alarm even with a normal temp gauge.

Ah, an interesting thread! Thanks chief. Good read, handy info.

Steve:
You have mounted the thermocouple on an intake manifold stud - the same place as I mounted mine on my Pajero (and for the same reason). You must remember that the thermocouple will detect the temperature of the component which it is fixed to, and also be influenced by what is going on around it.. In this case, it is the intake maniflod, being as close to the heat source as possible. However the air entering the engine will be cooling the manifold and will be giving you a false reading of the actual head temperature and also if the external air is hot, it will also read hot.

On my Pajero, I have found that the Watchdog shows a reading of 83 Deg C on a day of about 30 Deg C ambient temperature - WHEN I AM TRAVELLING AT 100 km/h. When I slow down for a town (50 or 60 km/h) the temperature goes up. In fact, I can see when the viscous coupling for the fan cuts in and out - it cuts in when the watchdog shows 83 Deg C and cuts out at 82. And when I am stuck in traffic, the temperature soars on a hot day - at one stage in Sydney whiclst towing my caravan through the hills around Galston etc, I had to temporarily increase the alarm setting (95 Deg C) because it was screaming at me. So was my wife! And when I stop the car, the heat sink effect sends the temperature skyward until the car starts moving again, or it cools down a bit. Installed in a Magna would probably be better than my Pajero because the thermocouple would not be exposed to the radiator ariflw to the same extent as what I get. Incidentally, when the ambient temperature is low (around zero), the unit displays a reading of about 50 Deg C, so it is a long way from triggering an alarm.

What I am trying to say is that although you have the potential to monitor the temperature with fairly good precision, the readings you get are really meaningless because external airflow over the thermocouple, the cooling effect of the incoming air inside the manifold and finally the immediate history of the car's operation will all affect the readings you get. Despite this, I believe that it is a great investment, because you (certainly I don't anyway) don't drive looking at the temperature gauge all the time. this thing does, and screams at you if it detects something wrong.

Incidentally, there is another device which detects low cooling water levels. This relies on an electrical device inserted into the radiator hose, and when the water level drops below the device, it triggers an alarm. I don't like this system because it then gives an electrical connection to the coolant and couldpossibly generate some circulating cuttents which could cause internal corrosion within the cooling system. I chose the Watchdog because I thought it offered the best protection for me.

Good points Erad.

The intake manifold bolt chosen is on a flange, so is isolated from the intake stream by a few cms. The location is also protected by airflow by the engine cover. I guess is might cause it to read high, especially when the car is stationary or in heavy traffic but won't be cooled by air flow at speed.

I guess it is a matter of working out some limits and using the device accordingly. It is interesting that the thermostat does seem to open consistently when the Watchdog displays around 85 degrees.

I'm keen to try it out on a 40 degree day.

Steve:
With the Magna, it is better than the Pajero because in my case, the thermocouple is almost directly behind the fan, so if anything, it is measuring the discharge temperature of the radiator rather than the engine head. Remember that the stud you have fastened the thermocouple onto is still a long way from the actual head, but this location is still better (I think) than the thermostat housing.

I would set the alarm at about 3 Deg C above the hottest you get to. You can easily increase the alarm setting should this be too close to operating conditions.

Another thing - I don't want another 40 Deg C day. I had a day in Sydney the other week when it was 48 and that was NOT funny. Sydney is bad enough on a good day, but 48 Degrees - that was too much.

That was the day my car had issues. Only 42.5 degrees here in Tamworth. I don't wish for any more but it would be a good test if we do get another hot spell. Rare for Sydney to be hotter than here.

It would be interesting, but not very cost effective, to connect a couple of Watchdog's to the engine. Now we're getting extreme!

I hadn't had a car overheat since my VH Commodore in 1992. I used to replace the water pump every 50000 km or so. They were pretty tough old iron things those engines. Horrible in every way though. When the water pump started to go, I'd top up the radiator with tap water for a few days before I got around to installing a new pump. Couldn't kill it (except the rust did eventually). I remember the pumps were crude old things. They looked like something from a Soviet 1950s factory. Thank goodness Aussie engineering has improved!

The Magna gave me a scare so I'm extra cautious now. Have always overserviced my cars but the Ralliart was the oldest car I have bought, so more uncertainty about its past treatment. Want to keep it in good nick. To look at it, it would be one of the best ones remaining. Wouldn't be the same with a 380 engine. Faster I know but not original......

There is a new Watchdog model just released. Backlit LCD with a few new functions. About $15 extra. Can control a relay for a thermo fan and has a twin sensor model to monitor the transmission. Auto backlight at light. Makers claim you can read it in direct sunlight (unlike the original).