What ambient temperature do Internal combustion...

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Seems like my cars like the 70s the best. They still run perfectly but seemy a bit more bogged down after 85 degrees Fahrenheit or so. I haven't really observed an mpg difference.
 
At 85F, you're probably running your AC, which saps some power from the engine. The smaller the engine, the more noticeable this will be.
 
True but if i have the a/c cranked at 70 degrees it still seems a bit more peppy. Both the 4 banger and the v6. Doesn't an engine inherently use cooler air more effectively though?
 
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Originally Posted By: badtlc
assuming you are talking MPGs, the hotter the better.


Yeah my truck runs great when it's 110 degrees outside with 100 percent humidity. Usually it feels like something is dragging behind me. Engineering 101 cooler air is denser thus give more power.
 
For emergency power generators that have their performance very carefully monitored and recorded, I'd say ambient temp means nothing once the system has reached full operating temperature for both oil and coolant.

For passenger vehicles I'd say that the length and frequency of trips is far more important than ambient temperature except when things get very cold outside. Vehicle engines like warm, even very hot ambient temperatures. Those very cold temperatures can be a real struggle for both the running gear and the people on board. Everything about cold weather operation is difficult.
 
So regardless of the ambient temp.by the time said air gets to the cylinders it's pretty much the same temp regardless of the temp of the air when it enters the air filter?
 
Originally Posted By: zach1900
Doesn't an engine inherently use cooler air more effectively though?

Theoretically, yes. Cooler air = denser air, which means more oxygen can be pumped into the engine. More oxygen allows more gasoline to burn, which means more power/performance.

But on the other hand, denser air also results in more air drag, especially at hwy speeds.
 
I'm accustomed to seeing lower fuel economy in the winter. Cold start enrichment and winter gas BTU content work against fuel economy.
 
I know i breathe easier the cooler it gets. I always assumed an ic engine does too.
 
Originally Posted By: zach1900
Seems like my cars like the 70s the best. They still run perfectly but seemy a bit more bogged down after 85 degrees Fahrenheit or so. I haven't really observed an mpg difference.


Probably the knock sensor causes the timing to retard.
The tendency of spark knock increases with higher intake air temp.
I get the same effect with my Matrix: a bit sluggish in hot weather.
As a test, during a heat wave when the ambient was around 100F, I ran a tank of 89 octane instead of the recommended 87.
It ran noticeably peppier, but no change in MPG.
 
There's no such thing as winter fuel or economy drop according to BITOG, you must be mistaken.
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Originally Posted By: riggaz
The higher the ambient temperature the hotter the engine oil will get.

Perhaps when the engine isn't one but when it's running the thermostat keeps it in a narrow range,no?
 
The engine oil temperature will track or follow the coolant temperature.

There is such a thing as the "equilibrium" temperature, which is the temperature at which the coolant reaches a point where it does not go any higher after the thermostat or coolant valve opens.

It will take longer to warm up in the winter, but if driven far enough, it will reach the "equilibrium" temperature.

It will take a shorter time to warm up in summer because the temperature of the fluids are already at a higher starting point.

Will there be short-lived, temperature "spikes" above equilibrium temperature? Of course there will, but the temps will come down as more coolant is circulated or when the airflow through the radiator is increased.
 
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Originally Posted By: riggaz
No chap, the oil temp doesn't stay the same as the coolant temp.


I never said that, I said "engine oil temp 'tracks' coolant temp."
 
For MPGs, the hotter the better. Warm air is less dense so the ECU will adjust to dump less fuel, to keep the A:F ratio the same. In addition, at higher ambient temps your oil and transmission fluid start out thinner contributing to less drag. Plus (at least, in theory), the air you are driving through is less dense so there will be less drag. Of course, if you have your windows down or A/C on, that works against fuel mileage.

For HP, the colder the better. Cold air is more dense so the ECU adjusts to dump more fuel to keep the A:F ratio the same. The engine will in turn make more power. This is one reason you get worse fuel economy in the winter (the other reasons are: winter blend fuel, more idling to warm up engine, denser air creating more drag, added weight of ice/snow, thickened oil and transmission fluid before warm up creating more drag, etc.)
 
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