Average running temp

[sikelsh]

It also depends whether you drive with Auto or Econ on, when I had my 1.8T it would drop about 10 degrees when driving with Auto on as the fan is always running.

Simon

[vindaloo]

My 1.8T seems to follow TC's pattern. Site between 94 & 98deg most of the time when running, below 90 seems too cool. Strangely enough when cruising on the motorway at 70 'ish it doesn't seem to make any difference if the aircon is on or off & yes my fan does work. It seems at cruising speed the airflow through the radiator negates the fan.

[T-Cut]

Originally Posted by kaiser

I would like to see some data for this claim, if possible.

The question's often asked, but is it ever answered? Over several years, I've searched the Net for hard data on optimal running temperature and it's surprisingly difficult to find. The vast majority of answers put onto forums for example are personal opinions based on superficial knowledge or anecdotal evidence. I think the answer is in the nature of 'It all depends on what you mean by - - -'.
Anyway, the 95-105C figure is partly through compiling figures gathered from this and other forums discussing running temperature. They typically fall into this ball park. They're primarily from petrol engined 75/ZTs, which have a nominal 88C thermostat and a cooling system all in good order. It's reasonable to assume that typical engines running without faults do so at the temperature range intended by MGR. I am also assuming that this is optimal. If it's not then we're back to square one. However, the diesel undoubtedly has issues with running temperature primarily because few seem to have anything like the temperature control of the petrols. Hence the experiments going on with different stat systems. Where increased running temperatures have been achieved, fuel efficiencies go with them. The best I've seen so far is a 15% increase in mpg. However, looking more broadly at discussions on diesel engines, by haulier groups for example, they do indicate that the ballpark I quote is where they prefer to be. The higher 'efficiency' of diesels per se doesn't mean they run more efficiently at a lower temperature than petrol engines. The thermodynamics of heat engines illustrates why (refs below).

It's also based on the results shown by research work done in universities and such that gets put on the Internet. These more obscure pieces tend to be in the later pages of Google searches. The bulk are mainly from forum chatter without much science.

You'll not find a specific reference that says 95-105C is optimal, but mentally collate it all, including the empirical data that can be found and it's about right. I'm talking specifically about water/glycol cooled internal combustion/piston engines of course. There are more thermodynamically efficient heat engines running at much higher temperatures. But we have to run within the mechanical constraints of our engines and the chemical limitations of their fluids.

Below area few of many references I found by judicious Googling for things like 'heat engines', coolant temperature', 'fuel efficiency', etc., etc. These are from an hour's searching following your query. I didn't keep a record of everything I read over the months past and some stuff now eludes me. Some of these are just basics and principles. Others more technical. I suppose time may tell whether my conclusions are correct but I'd be interested to hear alternative views.

http://en.wikipedia.org/wiki/Interna...engine_cooling

http://en.wikipedia.org/wiki/Heat_engine

http://galileo.phys.virginia.edu/cla...rnotEngine.htm

http://charming.awardspace.com/otto_...to_diesel.html

http://www.vincihiperformance.com/LS1%20TECH%20AND%20TUNE%20PAGE%20.HTML#Proper%20Co olant%20Temperature%20and%20Camshaft%20Life!

http://www.eng-tips.com/viewthread.c...=293813&page=3

http://umplib.ump.edu.my/images/mech/53.pdf

TC

[pab]

Originally Posted by kaiser

I would like to see some data for this claim, if possible.

Personally i think the evidence is pretty conclusive going on the findings of members over the years.

The figures i have achieved with my car over the same distance on the same commute seems to be very predictable..

I have studied information on this subject from other sources and found these matched my data of the coolant temperature leaving the cylinder head.

[kaiser]

Originally Posted by T-Cut

The question's often asked, but is it ever answered? Over several years, I've searched the Net for hard data on optimal running temperature and it's surprisingly difficult to find. The vast majority of answers put onto forums for example are personal opinions based on superficial knowledge or anecdotal evidence. I think the answer is in the nature of 'It all depends on what you mean by - - -'.
Anyway, the 95-105C figure is partly through compiling figures gathered from this and other forums discussing running temperature. They typically fall into this ball park. They're primarily from petrol engined 75/ZTs, which have a nominal 88C thermostat and a cooling system all in good order. It's reasonable to assume that typical engines running without faults do so at the temperature range intended by MGR. I am also assuming that this is optimal. If it's not then we're back to square one. However, the diesel undoubtedly has issues with running temperature primarily because few seem to have anything like the temperature control of the petrols. Hence the experiments going on with different stat systems. Where increased running temperatures have been achieved, fuel efficiencies go with them. The best I've seen so far is a 15% increase in mpg. However, looking more broadly at discussions on diesel engines, by haulier groups for example, they do indicate that the ballpark I quote is where they prefer to be. The higher 'efficiency' of diesels per se doesn't mean they run more efficiently at a lower temperature than petrol engines. The thermodynamics of heat engines illustrates why (refs below).

It's also based on the results shown by research work done in universities and such that gets put on the Internet. These more obscure pieces tend to be in the later pages of Google searches. The bulk are mainly from forum chatter without much science.

You'll not find a specific reference that says 95-105C is optimal, but mentally collate it all, including the empirical data that can be found and it's about right. I'm talking specifically about water/glycol cooled internal combustion/piston engines of course. There are more thermodynamically efficient heat engines running at much higher temperatures. But we have to run within the mechanical constraints of our engines and the chemical limitations of their fluids.

Below area few of many references I found by judicious Googling for things like 'heat engines', coolant temperature', 'fuel efficiency', etc., etc. These are from an hour's searching following your query. I didn't keep a record of everything I read over the months past and some stuff now eludes me. Some of these are just basics and principles. Others more technical. I suppose time may tell whether my conclusions are correct but I'd be interested to hear alternative views.

http://en.wikipedia.org/wiki/Interna...engine_cooling

http://en.wikipedia.org/wiki/Heat_engine

http://galileo.phys.virginia.edu/cla...rnotEngine.htm

http://charming.awardspace.com/otto_...to_diesel.html

http://www.vincihiperformance.com/LS1%20TECH%20AND%20TUNE%20PAGE%20.HTML#Proper%20Co olant%20Temperature%20and%20Camshaft%20Life!

http://www.eng-tips.com/viewthread.c...=293813&page=3

http://umplib.ump.edu.my/images/mech/53.pdf

TC

This is exactly my point. There is not evidence to state 95 to 105 degrees as an optimum range, so I think all should just realize that efficiency is not materially affected by temperature, as long as it is kept in check. Maybe the main reason for increasing running temperatures in combustion engines in the last decades is for pollution control.
So trying to run your engine extremely hot, just lowers your safety margin and gives you no thermal efficiency gains.
What does happen, at low temperatures, is that the fuel system thinks the engine is cold and over fuels to compensate. But there you would have to run far below normal operating temperatures, as you know, if you ever had a car with manual choke. The engine simply does not run well if run rich and hot.

I think we should be careful about stating things as clear-cut as is sometimes done. The fact is that many people here are not necessarily technical and may think they have a problem if their car runs 10 degrees lower than that stated, and that is not the case.