Operating Cylinder head temp on a TD5

BilboBoggles, I have recently bolted the same unit into a 'spare' threaded hole just below and behind the thermostat housing.

My normal operating temp ('99 300TDi) is between 77 and 85 degrees, with the gauge being nicely sensitive to minor changes in driving conditions.
Prior to getting my car dyno-tuned this morning (due to the fitting of an upgraded intercooler) it used to struggle to maintain 80km/hr going up Willunga Hill ( a long steep gradient south of Adelaide), and the TM-2 temp gauge on a typical 25 degree day would read 98-100 degrees by the time I reached the top.

Now with the car dynoed, she's pulling up the same hill today (30 degrees air temp) and holding 100 km/hr but at a cost... the TM-2 went up to 109 degrees (audible alarm going crazy!) by the time of reaching the top, but cooled quickly back to mid 80's shortly after.

However, having said all that, I'm inclined to agree with justinc about not being too concerned, given that the needle on the dash gauge had barely moved at all.

Of course it would be a different matter with prolonged stress on the motor, but short bursts into the 'red zone - wherever that is - should be ok surely!? Is that right guys?

I don’t think 97 deg C is anything to worry about in a vehicle with a cooling system in good condition.

Let’s remember most cars use is a mixture of water and antifreeze. As you know, adding antifreeze to water improves the boiling and freezing points significantly.

Comparisons:

• Pure Water - Boiling Point = 100 deg C

• 50/50 Antifreeze/Water - Boiling Point = 106 deg C

• 70/30 Antifreeze /Water - Boiling Point = 113 deg C

The temperature of the coolant can sometimes reach 121 to 135 deg C, however even with antifreeze added, these temperatures would boil the coolant. To further raise the boiling point of the coolant, the cooling system is pressurised. Most cars have a pressure limit of 14 to 15 psi, which raises the boiling point another 25 deg C so the coolant can withstand higher temperatures. So there's a lot more heat the coolant can absorb from the engine......

Does anyone know if the sudden drop in temperature as you crest the hill after a long, hard climb can cause problems? I seem to remember my father warning me that it can crack the head, but this was many years ago in the days of iron heads. I regularly tow a trailer up the SE Fwy out of Adelaide and at the top of the hill go straight from power on to power off. There's no opportunity to "ease off" as the gradient goes quickly from uphill to downhill.

Stephen.
'01 TD5 D2

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Originally Posted by StephenF10

Does anyone know if the sudden drop in temperature as you crest the hill after a long, hard climb can cause problems? I seem to remember my father warning me that it can crack the head, but this was many years ago in the days of iron heads. I regularly tow a trailer up the SE Fwy out of Adelaide and at the top of the hill go straight from power on to power off. There's no opportunity to "ease off" as the gradient goes quickly from uphill to downhill.

Stephen.
'01 TD5 D2

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it would be more of a problem if you pulled over and turned the engine off straight after climbing the hill hard, both for the turbo and cooling system.

From what I have read so far, the maximun normal reading for a block/head sensor is around 97 degrees and can go as high as 108 degrees under high stress conditions.

What we need to be aware of is that block sensors read engine shell temperature and not core or coolant temperature, which can be a lot higher.

If you need to check this, put the sensor in a metal kettle or pan and boil water in it & record the temperature.
Then fasten the sensor to the outside of the kettle or pan and repeat the experiment.

You will find a large difference in the temperatures as well as a significant time lag, this is also without a large engine fan blowing over the sensor.


Also if coolant is run close to boiling point and a hose or radiator cap lets go the pressurisation is lost and the risk of boiling is high.

Unfortunately the only true way to monitor engine temperature is via the coolant as it gives an instant reading.

By way of comparison, the TD5 ecu goes into low-power mode when the coolant temp gets to 121 degrees and reverts to full power at 118 degrees.

Davy, as you are probably aware the debate about low temp alarms - off the block or low coolant versions - has been dealt with at length on other threads. Let's just say that each have their clear benefits and its a matter of choice.

Personally I've been surprised as to just how quick/sensitive the TM-2 is to even minor changes in driving style and road conditions... the operating head temp (and corresponding reading) goes up and down virtually instantaneously and gives me a sense of security that goes beyond just low coolant problems.

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Originally Posted by omvanders

Davy, as you are probably aware the debate about low temp alarms - off the block or low coolant versions - has been dealt with at length on other threads. Let's just say that each have their clear benefits and its a matter of choice.

Personally I've been surprised as to just how quick/sensitive the TM-2 is to even minor changes in driving style and road conditions... the operating head temp (and corresponding reading) goes up and down virtually instantaneously and gives me a sense of security that goes beyond just low coolant problems.

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Horses for courses.... A low coolant alarm ensures you are warned when there is insufficient coolant in the system, regardless of engine temperature. This is useful for both gradual water loss over time and catastrophic failure. Sensors are typically located high up in the cooling system to ensure early detection.

Factory temperature sensors absolutely depend on adequate coolant being present in order to warn the driver of an overheating engine . A low coolant warning system (with both visual and audible alarms) can be classified as an early warning system. It ensures there is coolant circulating in the system and allows the factory gauge to work as designed.