Thread: Operating Cylinder head temp on a TD5

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

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

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.