I have been playing with my new SGII the last couple of days trying to perfect my warmup period in these 10- and 20-degree days and on the trip home from work tonight had one of those Aha! (or duh) moments for something that I haven't seen mentioned here. The first 3 miles or so home (2 of which were on the freeway @ ~55mph) the FWT barely inched up to about 150-155 degrees, but without really flooring it I couldn't get CHT above about 200-205. When I got off the freeway and started hitting the stoplights the engine revs obviously averaged lower than on the highway and the temps started dropping from there - thus couldn't get it to go EV because I couldn't hit that magic 153 FWT and 224 CHT combination to "trip the trigger". Then the AHA moment hit - turn off the heater !! As soon as I did that the FWT jumped to 165 and CHT went to 235 in about 30 seconds, and I slid right into EV as expected. Obviously the heater is getting it's heat from the engine coolant, so it's taking away that precious heat needed in the engine to get to the first EV levels and putting it into the cabin. Moral of the story - if you can stand the cold, keep your heater turned off until you hit the 153 FWT/224 CHT triggers to get you into the first EV. After that the minimum temps needed to hit EV goes down so you can turn the heater back on.

Chuck, in addition to what you just seen with the heater being on, I've posted about the electric heater pump in EV. With the climate control system in any position but OFF, there is an electric heater pump that will run and circulate coolant while in EV. There is a mechanical water pump that is belt driven by the engine. When the engine shuts off in EV, the electric heater pump comes on and provides heated coolant to the heater core. You must turn the climate control system OFF in order to stop circulation of coolant, even in the A/C settings.

If both pumps are off, the engine will stay hotter longer for EV driving. I leave my climate control system in the OFF position to save energy in EV mode all year long. The only time I run the electric heater pump is when I need the A/C. I did a bypass of the heater core so hot coolant doesn't circulate in the cabin duct system with the A/C on or using the outside vent fan. The cool air circulates longer in EV this way during hot summer weather.

There is a heater pump relay under the hood that can be removed to also shutdown this pump. I haven't put it yet to find out if I would get a warning light because I keep the system off most of the time. You could pull this relay and use the other features of the climate control without the electric motor running in EV I would think without any problems. Just haven't bothers myself. For those that have the electrical diagram manual, there is a good picture of where and which relay is for what system. Some of you recall I had 3 relays go bad, so I know they can be changed or pulled in a minute or so. I carry a spare now which cost ~$12.

GaryG

Thanks Gary - I never ran across that info in my searches. Good to know!

However, you have the advantage of living in Florida and being able to leave the heat off most of the time. Here in Minnesota it makes life a bit more livable if we can have heat in the car once in a while , so we have to be able to fire that thing up every so often.

Seriously though, that's also still good info to know for the summers and maybe to use more manual control of the heater on some trips to try and eke out some more EV time.

This may be confusing but I have been able to go EV with a CHT at 188 and FwT at 154 early (5:40 am) in the day. This is after I have had the vehicle's engine block heater plugged in overnight. This frequently occurs within 1 mile of home.

2005 4WD Escape Hybrid

Best Interstate tank trip E20 MPG 34.6 for 271 miles along I-80 in Indiana and Ohio. May 2008

Best multiple road tank trip E20 MPG 36.2 for 202 miles in Southwestern Pa. July 2008.

Best multiple road tank trip E50 38.1 MG for 246 miles in Northern Wisconsin Aug 2012

We all have conditions to deal with and I didn't want to imply you should freeze yourself to death. Since you posted about turning your heater off to go EV, I thought you and others may want to consider the entire heating and cooling system.

As for me in So. FL, my A/C compressor runs most of the time cooling the HV battery. Even this past week, my A/C compressor ran as soon as the engine started till it shutdown. The HV battery performs better if the cabin A/C is on for long EV driving also. The reason is the battery stays at the right temperature and doesn't get into the max limits to turn on the A/C compressor on. In other word, it doesn't have to play catch-up to cool it down. If it gets cold enough to turn on the compressor less, it may be better to leave the cabin A/C off for FE. Most of the time it's better to run the cabin A/C in very hot weather if your doing allot of EV as I do. Even the heater core bypass will not help you from turning the system on max. I think Carl can testify about that in Phoenix Arizona.

GaryG

Don't worry Gary - I understand what you meant.

That Florida vs. Minnesota quip was meant to be tongue-in-cheek, thus the

As for using the A/C in very hot weather, you mention it's better to use the cabin A/C if you're in EV a lot. Does that mean full A/C or just in econ mode?

Chuck,

I don't envy those cold temps., I lived in Boston for a while and I'm glad I'm not there during the winters anymore.

Are you using the recirculate option? I ask because heating outside air will be much harder than heating the cabin air alone. In (your) really cold temps. I'm thinking it would make a huge difference after the engine gets the any warmth in it.

Recirc actually tends to make matters worse most of the time in winter because it not only recirculates the air, but also the moisture within the cabin (and that which is created by your body) and it will fog/ice up the windows. Then you have to turn on the defroster (not good with an FEH) to get rid of it.

That's a bit of a Catch-22 there... I think I'd try cycling between recirc and outside air to see if I could minimize the impact of the cold outside air being heated and the moisture build-up from reheating the inside air. It would be a better solution than using no heat at all.

As with all hypermiling techniques, everyone must make their choice on how far they are willing to go for that extra FE.

Were it not for having to cool the batteyr pak I would readily advise disabling the A/C during the winter months and using a Home depot water flow shutoff valve to stop the flow of HOT water through the heater core in the summer.