Originally Posted By: bunnspecial
Originally Posted By: NoNameJoe
All good points!
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Also cold starts are hard on engines because of excessive fuel.
And that's purely for emissions? To warm up the cat faster? At what point does it stop being rich? I'm assuming the temperature just has to be enough for the system to go into closed loop and not full operating temperature?
Have you ever had a carbureted vehicle?
Generally, if the mixture is set correctly a car with a carb will not start easily when cold unless it is "choked." Basically, when you choke a carb what you're doing is increasing the vacuum in the throat which leads to a richer mixture and-as said-is easier to ignite. Ambient temperatures actually don't make a huge difference here-you'll often need to choke a cold car when it's 100º outside, although it certainly will be easier to start than when it's 0ºF. BTW, the carbed car I have now doesn't have a true choke, but does have a mechanism to enrich the mixture in the carburetors.
In any case, one of the principle problems-regardless of the fuel delivery mechanism-is that cold gasoline doesn't vaporize as easily as warm gasoline. Remember that only gasoline vapors burn, so by dumping more in(a richer mixture) you can actually get a mixture that burns.
A rich mixture is actually bad both for emissions reasons and for engine health. Rich mixtures dump out VOCs, CO, and can actually cook a catalytic converter(not generally a problem with fuel injection). A rich mixture also increases fuel dilution of the oil. The ECM will lean out the mixture as quickly as it possibly can in a fuel injected car for this very reason, although it will only do so in such a way as the engine will support it.
BTW, by the 1960s most American cars had automatic chokes, and I think for m/y 1975 it became a requirement for all US market cars for emissions reasons(prevent people from inadvertently choking it too long or forgetting to turn it off). My MG has a manual choke-I start the car fully choked(or with the fuel enrichment circuit fully engaged) and then once it starts I back off the choke as much as will support the car continuing to run. If I drive, the car reaches operating temperature in about 3 minutes or less, and as it warms up I back off the choke more and more. With an automatic choke, you typically push the pedal all the way to the floor to "set" it(on many carb designs, that also activates the accelerator pump to squirt gasoline into the intake and "prime" the engine). As the engine warms up, the carb either uses an electric heater or monitors the water temperature to take the choke off.
I know carbs are ancient tech in the automotive world now, but still the basic operating principles of a gasoline IC engine are the same regardless of the way fuel is delivered.
Interesting! Nope never had a carbureted vehicle. Learn something new here all the time.
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If car B warms up fully and gets a good run in it's weekly drive, then there should be no difference in lifespan, mile for mile.
Yup, at least a nice long drive is definitely reasonable once a week.
