I did a search and all I found was that a block heater heats the coolant in the engine. I made this a new thread for future reference rather than have it buried in my other thread.

For the purposes of understanding how using a block heater on a cold day would affect startup of the engine. If the heater is submerged in the engine coolant... and it's run over night the coolant would be 'warm' in the morning. The guage would reflect this meaning the ect is reading a warm temp. I've plugged mine in a couple times and when i start the car in the morning the guage reads around 55 or so. By comparison on a warm summer morning the temp guage will read cold(meaning not registering above 40deg).

From a physics standpoint i'm guessing that the block heater would raise the temp of engine parts(valves, rods, rockers etc) so that they would produce less friction and therefore start moving easier? Engine oil would be warmer as well would it not?

Given the ect is now reading a siginificantly warmer temp then normal... and assuming the IAT which is not directly attached to the block would be reading the ambient air temp... wouldn't this difference set off a code on startup(i've been told odbII systems are stickier on such differences). Even if it wouldn't throw a code i'm assuming it would create a strange fuel mixture for startup rather than a normal one for warm temps and a richer one for cold temps?

Help me understand how the block heater affects engine startup in cold weather?

 

A block heater keeps the engine parts warmed up (you already know this). It allows the engine to come up to temperature more quickly and allows for more instant heat. Your guess on the engine parts offering up less friction when kept warmer is also correct. Engine oil may be slightly warmer than ambient as well.

Given the relatively high temperature displayed on the gauge cluster (40*C =~100*F), you may or may not see an elevated temperature on the gauge upon initial start-up. That also depends on the wattage of the block heater as to how hot it will maintain the engine temperature. Your block heater sounds like it is pretty hot if it maintains the block at 55*C (~130*F).

And no, you will not get any complaining from the PCM about the temperature. ECT is used (along with IAT, MAF, and other sensors) to determine where in the fuel map to use for determining injector pulse width as well as spark advance, etc. Starting up your truck after sitting overnight with the block heater plugged in, keeping the block at 55*C is no different than starting your truck up after being up to temperature giving it time to cool down to 55*C. It is just a temperature that the PCM uses to help determine the appropriate IPW, advance, etc.

See my response to your other thread. I see where you are going.

 

Okay i understand(didn't think of it in terms of and engine cooling down, but started before completely cool)..thanks.

So things that can affect an engines ability to start in cold conditions...that a block heater would affect if run are:

-ect sensor(if reading warmer than ambient...if block heater heats engine to point where a leaner fuel mixture would start it)?
-weak spark condition?
-sticking injectors?
-other???

Things the block heater wouldn't likely affect that could otherwise affect cold starting:

-moisture in ingnition system(i.e. coil/cap).
-fuel pressure/regulation.
-timing.