But the stationary coolant is still hot right? I can't think that the coolant would get cold immediately.

My car is so old, it doesn't have a catalytic convertor :).

I use P&G on my way in (although have the water at 80 degrees C from the block heater on one of the journeys). I use 50% throttle, then cut the engine. I use less petrol, therefore less CO2 is produced, and my engine isn't in the warm-up phase. The engine warms up more quickly at 50% throttle for short periods compared to constant low-throttle driving.

Peakster - the air is heated by the engine coolant, which goes through pipes into a little radiator under the dashboard. The engine coolant is pumped by the water pump, which only works when the engine is running. So when the engine is off, you are using the heat in the water in that little radiator, which cools down quite quickly.

Do you have a grille block by the way? If not, it is a good way to get the car to warm up faster, especially when using P&G.

Edit - two posts since I started writing this :). Still some useful info though.

Yeah, I do have a grille block (see garage pictures), but I need to fabricate a better-sealing one. I wonder if I could change my water pump so it works when the key is in the "on" position when the engine is turned off?

If it is not too cool out then you probably should shut it off since you are burning gas at a high rate and going no where. This also give the heat that you already generated to spread into the colder ports of the engine a little more gradual. What kills me is the light at the end of the first block that I sit at while burning .5gph warming up all the time.

I would think it wouldn't get cold immediately..

Yeah, but he's talking a level of cold that you and I never see...

That's EXACTLY what I was thinking... I mean, 70-200F in a few minutes is quite a bit of stress for aluminum :P

But, as said in the first reply -- emissions are a concern too - waiting for the catalyst to heat up.... I think I'll split the difference and let my engine warm up 1/2-3/4 before shut down. We'll see what the meter says in a few weeks :P

As for the 90% of engine wear comes from start up.... I think a lot of engine wear comes from cold and dry start up, but 90% seems a bit high.

Thanks for all the response :D

Heating Up
 

I've noticed that cutting the engine and coasting will actually heat up the coolant temp while the coolant sits in the block jackets, unpumped. Didn't think about the Cat...

This is a good thread...

For emissions purposes, there's no way to know the Cat temp -- just coolant, IAT, or other parameters if equipped (oil temp).

I know some that P&G on warmup -- I guess it helps FE, not emissions. With the recent cold-snap here, I'll try the engine-on coast for warmup.

So, for the minority of us automatics, do we leave it in "D" to heat-up the transmission, or pop to "N"? The transmission needs heat too...

I don't have the answer - but that reminds me of another scenario -- Engine off - in gear coasting... Until today, I was doing this if I burned too long and there was a stop coming up... But earlier today I had an epiphany that doing so was just cooling down the exhaust/emissions equipment with cool air :/

Does anyone know if the programmers fully cut back on fuel when coasting (0% throttle, in gear cost down)? Or do they add a little fuel to keep emissions equipment warm and ready to go?

Engine braking = complete fuel cut.