Kia Plug-In Hybrid Q&A With Torque News Readers

The other day, a Torque News reader asked me a series of questions about Kia’s plug-in hybrids (PHEVs) vs hybrids (HEVs). I own a Kia Sorento PHEV and have written several articles about my experience with it, comparing it to other similar vehicles, and what kind of fuel efficiency results I get from it. This piece will address the reader’s questions by linking to other articles I have written and also includes new information I haven’t previously written about or that weaves the articles together.

First questions: how much have you needed to engage the gas engine for heat with your Sorento PHEV? In short, not a lot, but I live in the Seattle, WA area (like the reader who prompted this piece) and our winters are on the mild side (temps in the 30’s and 40’s are the usual for the two coldest months). I don’t have a precise figure, but the best I can estimate from my fairly meticulous documentation of fuel use is about 2 gallons (strictly for heat) over 9,000 miles. Of course, there were many times in which I was on a longer trip, driving in HEV mode, that I used heat but in those cases the heat comes from the gas engine as it runs to propel the vehicle, so it isn’t adding additional load it is simply capturing the heat that is already there from propulsion use. The reader also asked: does the gas engine engage when you're running A/C too? The answer is that it does not and the battery runs the AC. However, if you happen to be in the situation where you have depleted the hybrid battery (on a long trip for example) and you are running the AC, the gas engine will have to keep the hybrid battery charged enough to handle the electrical load from the AC. In such cases, if you are stopped at a light or in a parking lot with the car on, running the AC, the gas engine may fire up briefly to generate enough electricity to run the AC for several minutes.

Next question: Is the use of the gas engine for heat adequate for keeping the gas engine in good operating condition and do I foresee gas engines in PHEVs being adversely impacted by using them exclusively for heat? This is a very interesting, compound question and my opinion is no, I do not think the use of the gas engine to provide heat is bad for the engine in any way and I think it actually contributes to keeping the gas engine in working order. Here’s why I think this: in a PHEV, no matter how the gas engine is coupled to the rest of the driveline (if it runs only as a generator or if it actually propels the vehicle), the gas engine runs in cycles that are different than a non-hybrid gas engine. In other words, they spend more time at low(er) idles/RPMs than a regular gas engine would. This translates into gas engines in PHEVs being less “stressed” than those in non-hybrid gasoline cars. Less stress should typically prolong the life of the gas engine due to less wear on the metal and other components of the gas engine. Also note that hybrids (plug-in or not) are typically more thermally efficient than non hybrid gas engines (they have better lubrication/lower friction). One would have to know if the hybrid engines are built out of the same metals and materials as the non-hybrid counterparts though, to be absolutely certain, but I believe Kia uses the same 1.6 liter (usually turbocharged) gas engine in their hybrids as they do in their gas only vehicles. They may tune them differently in the hybrids (which may help keep engine RPMs in optimal ranges) and they may use different lubricants as well. As always, one should follow the maintenance directions in their manuals, which for the Sorento PHEV at least, includes regular addition of fuel additives that clean the engine’s valves and combustion chambers in particular, something that may be more likely to get “gummed up” due to short duration/less frequent use.

Next question: What difference in combined mpg/range (EV and HEV) do you experience between warmer and cooler seasons, particularly in HEV mode? In warmer months (which I define in my home region as any month where the averaged daily temperature is 50 degrees or warmer, or about 7+ months of the year), I have typically achieved electric only range in the low 40’s in miles of range in my Sorento PHEV. In colder months, the lowest EV only range I have seen is a little under 30 miles (note this was with studless snow tires on, too, which have greater rolling resistance and thus decreased efficiency compared to all season tires). My mpg figures vary depending on external temperatures, but more so from how I am using my Sorento PHEV. If it is summer and I am going on a camping trip with a cargo box on the roof and a full load of people and stuff, or winter road tripping to spend the holidays with family, I may see between the low 30’s to mid 40’s mpg in HEV mode, but trend away from the lower end of the range on short, daily commuting types of drives. During colder months, it is more likely that I’ll see lower mpgs in hybrid mode, but it always seems how I drive makes the biggest difference. If I am driving mostly on the highway at speeds above 50 mph, my efficiency is lower. If I am mostly driving at speeds less than 50 mph, my efficiency is better. But this is sort of a universal rule for any vehicle; driving fast uses more energy (and “fast” basically starts around 50 mph). My lifetime average fuel economy, running on gas, is about 36.4 mpg. My calculated lifetime average EV range is 37.3 miles (calculated as my cumulative miles per kWh x the usable capacity of the hybrid battery which is 11.8 kWh). My lifetime blended fuel economy, over 9,000 miles using both electricity and gasoline, is 69.4 mpg. Not bad for a vehicle weighing more than 2 tons and basically shaped like a chipped brick.

But the reader asked about my blended (i.e. electric + gasoline) efficiency and what difference if any I see between warm and cold seasons. If it wasn’t obvious from the rest of this paragraph, it is actually not how I keep track of my fuel efficiency (my figures trace driving patterns, not temperature specific results). For example, I didn’t take any drives that exceeded the range of a full battery charge in February this year, and used less than half a gallon of gas (and close to 90 kWh) to drive 257 miles (mostly for heat, but also a little due to stepping on the throttle hard enough to force the gas engine on twice). What was my blended fuel economy? It was outstanding. But what is my best estimate of what figures I would see on a trip where I drove say, 50-100 miles using up a full charge of the battery and the rest on gas? If you follow some of the links above you’ll get figures for such scenarios, including that range and longer, but I would say in winter my range would likely be in the 50-70 mpg combined for a trip on the lower end of that range, and more like 33-43 mpg combined closer to the top end. The longer the trip though, the less variance there is. For example if I was doing a 300 mile drive in winter in one go, I would expect to see mpgs in the lower 30’s, combined. For the same drive in the warmer parts of the year, I might see 34-37 mpg combined (attained only by driving the speed limit or close to it and accelerating gently/not carrying obstructive cargo on my roof, etc.).

I will continue addressing more reader questions in a follow up article. Please leave any questions or comments you may have so far, below.

Images courtesy of Kia and Justin Hart.

Justin Hart has owned and driven electric vehicles for over 15 years, including a first generation Nissan LEAF, second generation Chevy Volt, Tesla Model 3, an electric bicycle and most recently a Kia Sorento PHEV. He is also an avid SUP rider, poet, photographer and wine lover. He enjoys taking long EV and PHEV road trips to beautiful and serene places with the people he loves. Follow Justin on Twitter for daily KIA EV news coverage.