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Best Operating Temp?


Best Answer unburntfuelinthemorning , 18 October 2019 - 09:59 PM

Interesting information but the way I read the original question the OP was asking about operating temperatures when using modern fuels containing ethanol and if this makes a difference compared to standard unleaded without ethanol.

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#1 croc7

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Posted 18 October 2019 - 06:01 AM

Considering ethanol ‘enhanced’ modern fuels are everywhere and the A series engine’s combustion chamber efficiency, what would be the target operating temperature for a moderately enhanced street engine?

#2 unburntfuelinthemorning

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Posted 18 October 2019 - 06:31 AM

Do you mean coolant operating temperature?



#3 croc7

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Posted 18 October 2019 - 07:44 AM

Yep

#4 unburntfuelinthemorning

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Posted 18 October 2019 - 08:16 AM

I don't know. 

 

As far as I understand, petrol engines would have a higher thermal efficiency if they ran much hotter than they do but cannot due to the limitations of the materials involved.

 

Engines are often run at lower temperatures such as for racing for maximum power probably because the air density increases as a result of the generally lower engine temperatures but the efficiency then falls away.

 

I would say the answer to your question is that the target operating temperature of the coolant is very similar to the requirements when using standard petrol.

 

More likely to need small changes would be the air/fuel mixture and ignition timing. 

 

I wonder if ethanol moves the stoichiometric ratio away from the 14.7:1 ratio of standard petrol?



#5 Steve220

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Posted 18 October 2019 - 08:41 AM

I don't know.

As far as I understand, petrol engines would have a higher thermal efficiency if they ran much hotter than they do but cannot due to the limitations of the materials involved.

Engines are often run at lower temperatures such as for racing for maximum power probably because the air density increases as a result of the generally lower engine temperatures but the efficiency then falls away.

I would say the answer to your question is that the target operating temperature of the coolant is very similar to the requirements when using standard petrol.

More likely to need small changes would be the air/fuel mixture and ignition timing.

I wonder if ethanol moves the stoichiometric ratio away from the 14.7:1 ratio of standard petrol?


It does. 10% ethanol drops it to roughly 14:1.

#6 leyland73

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Posted 18 October 2019 - 10:12 AM

I use an 82 degree thermostat year round in all my A series engines, have done for years. I think with the increased ethanol content we need to be looking at hotter spark plugs.

#7 Ethel

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Posted 18 October 2019 - 10:12 AM

It's an interesting question. I don't have an answer but you could look at what thermostats are rated at for newer engines designed to run on the stuff



#8 gazza82

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Posted 18 October 2019 - 10:31 AM

I think my old '98 Alfa had an 88C thermostat. Fans were set to cut in at 92C and 98/100C (low and high speed)



#9 Dusky

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Posted 18 October 2019 - 11:47 AM

Depends what you want. Power or economy. Loads of engines are running 100-110°C atm.

#10 unburntfuelinthemorning

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Posted 18 October 2019 - 12:20 PM

I think with the increased ethanol content we need to be looking at hotter spark plugs.

Why do you think hotter plugs would help?



#11 leyland73

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Posted 18 October 2019 - 05:45 PM


I think with the increased ethanol content we need to be looking at hotter spark plugs.

Why do you think hotter plugs would help?


#12 leyland73

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Posted 18 October 2019 - 05:57 PM

Doh, meant cooler running plugs not hotter. Unleaded fuel burns hotter than old fashioned four star. Hotter burn cooler plugs

#13 Orange-Phantom

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Posted 18 October 2019 - 08:38 PM

People say the 88oC thermostat was introduced for unleaded petrol yet it was introduced for the Mini in 1976 when the emission regulations were tightened.  Max Power out of an A Series is when it's run at 70 oC which is why most race engine builders use and recommend 74 oC thermostats and that's still on unleaded fuel.  The 74 oC thermostat is not suitable for road use though, as it won't get the engine up to a hot enough temperature to burn off the contaminates in the oil.

 

Out of all the evidence I have seen for temperature of thermostats this guy here seems to have nailed it at 82oC which is what it used to be before the emission regulations were tightened in 1976 and they swapped to the 88oC thermostat. 

 

http://www.carnut.co...blin/cool3.html

 

Keith Calver states that maximum power from an A Series is at 70-75oC.

 

http://www.minimania...emperature_1506

 

I've seen no evidence anywhere that states that unleaded needs a higher temperature engine to burn or operate properly and certainly nothing to say that leaded fuel produces more power at lower temperatures compared with unleaded.  As said before the 88oC thermostat was introduced for all Mini's in 1976 for emission purposes and this was when cars were still running leaded fuel.

 

To quote this Race Fuel manufacturer "Lead does not have any significant effect on overall combustion properties.  This allows us to specify certain hydrocarbons in a blend to achieve desired fuel properties, then add varying amounts of lead to target a an octane level.  This is why the myth about high octane fuels burning slower is exactly that – a myth".

 

https://www.sunocora...ed-racing-fuels

 

Also some good articles in general from the same source

 

https://www.sunocora...m/tech-article/

 

I cannot find any evidence that the unleaded / hotter engine temperature thing is based on truth or is it just one guys opinion which has been repeated enough times over enough forums to become fact?  If someone can point me to some actual hard evidence that unleaded fuel requires a hotter engine temperature to burn / function properly I'll more than happily revise my thinking on the matter.

 

So… to surmise….

 

74oC Max Power.  Competition use.  Not suitable for road use as the oil won’t get hot enough to burn off contaminates and also increased engine wear.

 

82oC Sweet Spot.  The best compromise thermostat for an engine between power, engine wear and to have the engine oil hot enough to burn off contaminates.

 

88oC Best for Emissions.  Introduced in 1976 due to tightening emission regulations (and not for unleaded fuel (as incorrectly stated many times) as everyone was still running leaded fuel back then)!  Also if you use your car in winter then an 88 degree thermostat may be beneficial especially if you want some heat out your heater!



#14 unburntfuelinthemorning

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Posted 18 October 2019 - 09:59 PM   Best Answer

Interesting information but the way I read the original question the OP was asking about operating temperatures when using modern fuels containing ethanol and if this makes a difference compared to standard unleaded without ethanol.






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