Engine temps: what is considered "too hot" for efficiency?
05-02-2008, 11:12 PM
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Engine temps: what is considered "too hot" for efficiency?
OK, none of my hot rod stuff here. I'm actually working for efficiency and mpgs.
Car in question is an 03 Cavalier. 2.2 Ecotec w/ 4 speed auto. With a commute and large gas prices in my face, I'm trying to do some simple mods to this car to increase my MPGs. One area I'm currently playing with is aerodynamics. I've made some block off covers for my front grills, and with the decreased air flow I've seen increased engine temps. Max I've seen is 225 degrees. Red zone on factory temp gauge is around 260 degrees. I run Amsoil 0-20 synthetic oil, and don't beat on the car. The grill covers are simply cardboard and duct tape, so I can easily open them up for air flow if I'm running too hot. But my question is, just what is "too hot?" I'm not over heating, performance is good, and the temp never stays as high as 225. I'm also somewhat under the impression that a "hotter" engine is better for efficiency. So, what do you gurus think?
Car in question is an 03 Cavalier. 2.2 Ecotec w/ 4 speed auto. With a commute and large gas prices in my face, I'm trying to do some simple mods to this car to increase my MPGs. One area I'm currently playing with is aerodynamics. I've made some block off covers for my front grills, and with the decreased air flow I've seen increased engine temps. Max I've seen is 225 degrees. Red zone on factory temp gauge is around 260 degrees. I run Amsoil 0-20 synthetic oil, and don't beat on the car. The grill covers are simply cardboard and duct tape, so I can easily open them up for air flow if I'm running too hot. But my question is, just what is "too hot?" I'm not over heating, performance is good, and the temp never stays as high as 225. I'm also somewhat under the impression that a "hotter" engine is better for efficiency. So, what do you gurus think?
05-03-2008, 06:55 AM
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Bob: good topic. Sorry that I don't have any answer. I do have the same general impression - that it's more efficeint when it is hot. But much more than that I can't say except that 225 is not "too hot". Water jacket temps really mean very little anyway. Sorry I can't really help with your question.
Rich
Rich
05-03-2008, 03:06 PM
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Bob,
The answer to your question will be very engine specific. Although
there are benefits to additional engine heat, there are also limits.
Reduced component life because of the elevated temperatures is
secondary. The primary concern is auto-ignition. As the CHT goes up
so does the end gas temperatures. During combustion the unburned air
fuel mixture ahead if the flame is highly compressed, this equates to
very high temperatures in the region. When elevated CHT puts this end
gas temperature above the limits of the fuel in use, auto-ignition will result.
The answer to your question will be very engine specific. Although
there are benefits to additional engine heat, there are also limits.
Reduced component life because of the elevated temperatures is
secondary. The primary concern is auto-ignition. As the CHT goes up
so does the end gas temperatures. During combustion the unburned air
fuel mixture ahead if the flame is highly compressed, this equates to
very high temperatures in the region. When elevated CHT puts this end
gas temperature above the limits of the fuel in use, auto-ignition will result.
05-03-2008, 05:53 PM
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As coolant and cylinder wall temps increase the efficiency of heat transfered from the combustion space will decrease. The efficiency of the heat transfer is basicly related to the temperature difference and the surface area available for transfer at a given time. Reducing heat lost to coolant will increase the thermal efficiency of your engine and thus increase your gas mileage. Thermal efficiency by definition is net work out divided by heat addition. Heat added is calculated by multiplying the lower heating value of the fuel and the fuel mass. Net work would be brake mean effective pressure times swept volume.
If you want better mpg, slow down when you see a red light ahead, do whatever you can to avoid a total stop. its better to just lose enough momentum from 60-40 rather than lose the momentum from 60-0 just because you want to hurry up and stop like so many do. The other thing is use the cruise control as much as possible and keep your speed to a minimum, change in power from aero drag is related to velocity by the velocity cubed so small percentage changes in speed lead to huge changes in power to overcome drag. I know on my fbody drag doesnt really become significant until after about 45mph. Graphing airflow vs mph at cruise states is a pretty eye opening thing if you can find a flat road to test on during a still day and have a data logger. The last thing is dont lug your motor if its a manual keep the rpms up a bit, friction on that small an engine is not going to be a big deal, but lug the engine and its going to take more air and fuel to move the thing.
If you want better mpg, slow down when you see a red light ahead, do whatever you can to avoid a total stop. its better to just lose enough momentum from 60-40 rather than lose the momentum from 60-0 just because you want to hurry up and stop like so many do. The other thing is use the cruise control as much as possible and keep your speed to a minimum, change in power from aero drag is related to velocity by the velocity cubed so small percentage changes in speed lead to huge changes in power to overcome drag. I know on my fbody drag doesnt really become significant until after about 45mph. Graphing airflow vs mph at cruise states is a pretty eye opening thing if you can find a flat road to test on during a still day and have a data logger. The last thing is dont lug your motor if its a manual keep the rpms up a bit, friction on that small an engine is not going to be a big deal, but lug the engine and its going to take more air and fuel to move the thing.
05-03-2008, 06:15 PM
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I think 225 is a little on the too hot side. Modern EFI engines normally operate at 195. Engine fans don't usually turn on until 205. Your hot engine may be good for emissions but performance will be lower.
05-03-2008, 07:34 PM
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The key to engine efficiency is to reduce burn time (increased engine
temperature will do this). An engine modification that allows a reduction
in ignition advance yet develop peak cylinder pressures while the piston
in a favorable position to generate power (~ 15 – 20 degrees ATDC). The
result is a reduction in overall pressure rise BTDC reducing negative work.
temperature will do this). An engine modification that allows a reduction
in ignition advance yet develop peak cylinder pressures while the piston
in a favorable position to generate power (~ 15 – 20 degrees ATDC). The
result is a reduction in overall pressure rise BTDC reducing negative work.
05-04-2008, 10:11 AM
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05-04-2008, 10:25 AM
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If they could have made it more fuel friendly from the factory but making it run hotter, then wouldn't they?
I think you are riding around with card board and duct tape on your car for no reason, and probly about to pop a head gasket, b/c its not even summer yet and its running 225.
Bob, I know you have plenty of money.......I don't even know what your worried about. I don't even own a vehicle that gets double digit mileage. And I'm poor
I think you are riding around with card board and duct tape on your car for no reason, and probly about to pop a head gasket, b/c its not even summer yet and its running 225.
Bob, I know you have plenty of money.......I don't even know what your worried about. I don't even own a vehicle that gets double digit mileage. And I'm poor
05-04-2008, 03:12 PM
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If they could have made it more fuel friendly from the factory but making it run hotter, then wouldn't they?
I think you are riding around with card board and duct tape on your car for no reason, and probly about to pop a head gasket, b/c its not even summer yet and its running 225.
Bob, I know you have plenty of money.......I don't even know what your worried about. I don't even own a vehicle that gets double digit mileage. And I'm poor
I think you are riding around with card board and duct tape on your car for no reason, and probly about to pop a head gasket, b/c its not even summer yet and its running 225.
Bob, I know you have plenty of money.......I don't even know what your worried about. I don't even own a vehicle that gets double digit mileage. And I'm poor
And since you know I have plenty of money, please show me where it is!
If I had plenty o' bux I wouldn't be driving a 5 year old "Gramma" car, and I wouldn't be looking for a part time job! Yup, ubg might be flipping that burger you are ordering at McDs! 
05-04-2008, 03:48 PM
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The easiest enemies of fuel efficiency to defeat are weight and rolling resistance of the vehcle, and drving style of the driver. I liked what WS6T3RROR said about keeping up momentum. I have heard it said as drive farther ahead of the car than the hood ornament.
On 8 Mile Road the lights are about 1/2 mile apart in some areas and most everybody accelerates, cruises, slows down and stops when going from light to light. I have been trying to stay in a lane where I can maintain a fairly constant speed without getting run over and never have to get below 30. It doesn't make too many other drivers happy and they give me a lot of one finger salutes, but it does save gas.
If you can stand the ride, inflate your tires to the maximum pressure shown on the sidewall. That is probably 44 psi. Don't hit any potholes with that pressure. Take all of the junk out of the car. Every pound you have to accelerate costs more gas. Spare tires and jacks are dead weight. That's why you have AAA. I don't know what you look like, Bob, but if you are 'stout', consider losing weight. I don't take my own advice on this but I have my pizza delivered which saves my gas.
From what I have read, you probably don't want to run your production car much above 200-210 degrees.
Joe Urban
On 8 Mile Road the lights are about 1/2 mile apart in some areas and most everybody accelerates, cruises, slows down and stops when going from light to light. I have been trying to stay in a lane where I can maintain a fairly constant speed without getting run over and never have to get below 30. It doesn't make too many other drivers happy and they give me a lot of one finger salutes, but it does save gas.
If you can stand the ride, inflate your tires to the maximum pressure shown on the sidewall. That is probably 44 psi. Don't hit any potholes with that pressure. Take all of the junk out of the car. Every pound you have to accelerate costs more gas. Spare tires and jacks are dead weight. That's why you have AAA. I don't know what you look like, Bob, but if you are 'stout', consider losing weight. I don't take my own advice on this but I have my pizza delivered which saves my gas.
From what I have read, you probably don't want to run your production car much above 200-210 degrees.
Joe Urban
05-04-2008, 04:48 PM
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Bob:
Check the Evans Coolant site... I think he is a proponent of elevating the engine operating temp to improve efficiency, and uses the properties of pure propylene glycol to achieve that, without increasing the tendancy for detonation.
http://www.evanscooling.com/catalog/C_npg1.htm
http://www.evanscooling.com/html/tech1.htm
Check the Evans Coolant site... I think he is a proponent of elevating the engine operating temp to improve efficiency, and uses the properties of pure propylene glycol to achieve that, without increasing the tendancy for detonation.
http://www.evanscooling.com/catalog/C_npg1.htm
http://www.evanscooling.com/html/tech1.htm
05-05-2008, 12:33 AM
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True... also, ceramic coating the combution chamber & piston head also increases the heat retained in the cylinder gas... and hense more power/heat used increase efficency. Higher coolant temps reduce the heat taken out of the combustion chamber... and likewise increase efficiency.
Probably not a great thing for hp, and too hot is obviously a problem for rubber under the hood... but for MPG it may help a bit.
Probably not a great thing for hp, and too hot is obviously a problem for rubber under the hood... but for MPG it may help a bit.
05-05-2008, 11:26 AM
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Interesting stuff; I never knew the extra heat will help mileage... I took a more indirect approach and looked at things other than my vehicle that I drive to work. I ride a motorcycle everyday it doesn't rain, and I only go about 10 miles to work and back, so its not a big deal to me to increase my efficiency. But since I lead a boring life at the North Carolina Dept of Transportation every weekday, I looked into the Traffic Control section and found out how the lights work on the route I take to my job. I can either take the Beltline around Raleigh (15 miles to work) or go straight through the city down the road I live off of, (10 miles) The beltline is usually quite busy at 7:00 in the morning, so I opt for the city streets near NC State Univ, because every college kid but myself gets to sleep in.
Anyways, I found out that for the route I take, which is one road all the way down to the NC-DOT, the lights are set to be green if you keep a constant speed of 35 mph at the time that I am going to work. Knowing that I keep that speed up and get through about 80-90% of the 27 lights I go through each day to work and the 27 I go through on the way back home
(Obviously, I'm the only one that knows the secret, so I still have to stop at some lights for the traffic that keeps up with the 45 mph speed limit through the stretch, therefore hitting quite a few of the lights...)
Maybe you and anyone else interested in better city mpg would be able to look into your routes (if they are fairly direct and don't require many turns) and your DOT will be able to help out. I got 60+ mpg last tank; 200 miles on 3.3 gallons
Anyways, I found out that for the route I take, which is one road all the way down to the NC-DOT, the lights are set to be green if you keep a constant speed of 35 mph at the time that I am going to work. Knowing that I keep that speed up and get through about 80-90% of the 27 lights I go through each day to work and the 27 I go through on the way back home
(Obviously, I'm the only one that knows the secret, so I still have to stop at some lights for the traffic that keeps up with the 45 mph speed limit through the stretch, therefore hitting quite a few of the lights...)Maybe you and anyone else interested in better city mpg would be able to look into your routes (if they are fairly direct and don't require many turns) and your DOT will be able to help out.
I got 60+ mpg last tank; 200 miles on 3.3 gallons