EV mode and the effect on MPG

I've had situations where it's done both.

Lately, in the morning, my first 1/2 mile is downhill residential. I've found that using the EV button until I get to the main streets where the speed limit is 45-50mpg can help me get a 50+mpg first 5 minutes. The second 5 is almost as high while the ICE warms up.

In others where I may use it to go around parking lots, and have my A/C cranking will hurt since the next time the ICE has to work even harder to get the charge back up to a happier level.

Knowing when to use it is key to improving MPG.

-Rick

 

One thing to remember, however, is that the ICE's warmup cycle is about the first 60 seconds or so which is prefers to run at an idle speed with retarded timing in order to heat the catylitic converter as quickly as possible.

W/o EV mode, you'll notice that light pedal pressure uses battery power even though the engine is idling (engine RPM never varies). Only after a minute or so will the engine suddenly spin up to "help". The classic did the same thing, but it had the benefit of the HC absorbing catylitic converter to prevent as much from coming out the pipe (I could tell, the '02 had practically zero soot on the pipe at 30k miles, my '04 had some at 5k).

By using EV, then requiring the gas engine almost immediately once we're done w/ our low speed, the initial start isn't gradual for warmup (or oil), but more immediately going to work, which in the end, may not be as good for the engine or emissions. So while we're getting better MPG, it may be sacrificing cold-start emissions performance.

One exception to that is if the hot coolant from the storage tank sitting longer in the head is allowed to heat the engine more thoroughly, negating that need for the additional warmup. I wouldn't know how ot test this though since the '04 doesn't have the cold coolant light like the classic did.

An interesting topic indeed

 

Yes, I think that's fair to say. Let me describe a common use for the EV button I have--when it's worked out well, and when it hasn't....

From work where I park in a parking garage I like to use the EVb when leaving b/c there are at least 5 stops in about 1/2 mile as I leave the hospital campus. If/when the ICE comes on for warm-up it never gets to spin up to optimum RPM/cruise speed b/c my speed never exceeds about 25mph and I'm stopping and going again repeatedly. The last on-campus stop merges onto a main city street with a speed limit of 35mph.

When things go well I use EV all the way to that last stop. Exit EV when it's my turn to pull onto the main roadway, then, if I can avoid 1 more light about 1/2 mile down that road I stay at a steady speed for at least 1 mile of 35mph. By the time I've gone about 2-3 miles the HV has fully, or nearly so, recharged. I usually see my first 2 5 minute bars at or just below 50 mpg from a cold start.

When things do NOT go so well, on a gradual incline after one of the first few stop signs, but with 2 stops left I'll get a little too aggressive on the accelerator and ICE will kick in. It will stay on for the next 2 full lights even with the car stopped. I'll see 5 min bars below 25mpg often b/c the HV has drained enough that the ECU sees it as a problem and prolongs the warm-up cycle to recharge. My 2nd 5 min bar is usually around 50mpg. Also, sometimes I hit that other light 1/2 mile down the main road and the situation is similar, if not more dramatic b/c the HV will be down to around 3-4 bars and thus even more aggressive recharging.

It's interesting that if/when you can continue at a steady speed that the ECU doesn't seem to be as aggressive/eager to recharge the HV--sort of like it's saying "He's driving along just fine, I'll get my chance to recharge latter, let's optimize mpg for now". Whereas with the stop and go driving it seems to say "Geez, what's this guy doing, I better charge up or I may run low if he decides to drive like this all day."

I think "the couple miles" is too far to make this a benefit. I'd say that if that couple miles is relatively long stretches that you're better off just starting up like normal. If it's all downhill like Rick's situation that's a different situation, but you're doing to have to deeply D/C your battery to go that far and likely won't make it and then end up in situations like I have when things 'don't go well'. My drive from home involves about 1/4 mile gravel road to a stop sign, then a 1/4 mile downhill then 1/4 mile uphill to a stop, followed by another 1/4 mile down hill...all at 45mph top speed. Then I merger onto a main drag with 1/2 mile uphill before things start gradually leveling off. Although it would seem like I could take advantage of EV, I just find it too tricky to efficiently do so, I'd be nursing the accelerator too much and probably not gain too much. I'd NEVER make it 2 miles, maybe 1 1/2 miles if I were lucky.

That's a decent choice, and I do use EVb on my way home on that same gravel 1/4 mile road to my house for the exact reasons you describe. There is a gradual incline on my driveway and the build up to street-speed from the turn onto that road almost always caused ICE to kick on for 10-15 seconds unnecessarily. Now I go into EV just before the turn, use a little battery to get up to about 20mph, then I coast "no arrows" to my driveway, use a little battery to get up the little slope and coast into my garage--never seen a drop of even 1 bar on the Energy screen for this stretch.

Sorry to be so long winded, hope that gives you a little better sense of what the EVb can and can't do in real world daily driving.