It Ain’t Easy Being A Hybrid Engine

October 19, 20242 months ago Jennifer Sensiba 0 Comments

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A recent video over at the Engineering Explained YouTube channel shares a fact that may surprise many readers: the engines in hybrids have a rougher life than those in normal non-hybrid ICE vehicles. While it’s true that they’re spared some of the worst punishment an ICE typically suffers, there are some things about sharing duty with an electric motor that make it tough to stay around for the long term.

Let’s look at the video first, and then I’ll summarize it for people who can’t watch a video right now and discuss things a bit.

How Hybrids Work

If you’re not familiar with how a hybrid works, Engineering Explained goes over that real quick. In short, a hybrid has both EV and ICE systems that share the work of going down the road. In most cases, this is a parallel system, where either system (EV or ICE) can directly contribute to mechanically turning the wheels.

What he doesn’t cover in this video (for the sake of brevity and simplicity), is that there are other forms of hybrids. Series hybrids only have electric motors turning the wheels, with an ICE engine or some other source of power (like hydrogen) charging a smaller battery. “Serillel hybrids” like the Chevy Volt can operate either as series hybrids, parallel hybrids, or even kind of like an ICE car in some situations depending on what’s most efficient. There are also oddball arrangements like “through the road” hybrids where different pairs of wheels have different types of drive systems that don’t touch each other.

But, in each of these cases, the work of the engine should be lighter than in a normal ICE car, right? I mean, they’re getting some help and a boost from the EV system that takes some of the stress away, so you’d think that they have it easier. Plus, there are now Toyota hybrids over 20 years old that just don’t want to die as long as you keep giving them refurbished battery packs, so it must be easy on the engine, right?

What Challenges They Face

It turns out that while there are ways in which there’s lower stress on an ICE powerplant in a hybrid, there are ways in which a hybrid’s engine has it a lot harder.

One challenge is start/stop cycles. Because oil pressure isn’t right, temperatures aren’t optimal, and other factors, most of the wear an engine suffers happens during starting and stopping. Dry or thermally unexpanded bearings and piston rings cause a lot more damage than one that’s in ideal conditions. Hybrids save a lot of fuel by turning the engine off when it’s not needed, but it comes at the cost of going through another cycle of extra wear that can really stack up over time. This is worse for cold starts than it is for hot starts.

Another big challenge is that water gets into the oil. Because metals get larger as they heat up, hot engine parts are not quite the right size when a motor gets colder. This leaves gaps in the piston rings that can allow some of the exhaust gas to blow by and get into the crank case, where the engine’s oil is stored. Exhaust gas contains water (all combustion reactions result in at least CO2 and H2O), so when the steam condenses (at lower temperatures hybrid engines can get to), some water ends up in the oil. This isn’t great for bearings and the walls of the pistons, as it keeps oil from coating everything and flowing properly (oil and water doesn’t mix).

Finally, fuel also tends to find its way into a hybrid engine’s oil more than in a typical ICE car. Just like water from the exhaust, fuel sprayed into the cylinder along with air can leak down the sides of the cylinder wall and down into the crank case when there isn’t a good seal. This can both wash away oil (accelerating wear) and contaminate the oil.

How These Challenges Can Be Mitigated

The wear from starts and stops isn’t as bad as it might seem at first glance because some oil stays in place for several minutes. This helps things get back to ideal a lot faster than a vehicle that has been sitting overnight. The same is true for hybrids that regularly run the engine when it comes to getting fuel and water in the oil, as the piston rings are generally closer to temperature than a cold start, limiting blowback compared to a cold start.

But, these problems are still very real, and there are answers for them.

Temperatures can be mitigated by basically putting the engine’s coolant in a thermos-like insulated container. By storing hot coolant during engine stops and pumping it quickly back into an engine’s coolant passages, an engine can be brought back to temperature a lot more quickly.

Water contamination can be mitigated with additives that help demulsify oil and water to prevent engine oil from becoming too egg-like. This gives time for the oil to heat up and turn the water back into steam and expel it from the engine via the PCV valve system. So, if a hybrid car’s manual recommends special oil, follow the recommendations! Fuel can be protected in a similar way, by using additives to protect the surfaces from accelerated wear and fuel washing. Oil has to be designed to find a good balance to suit the special needs of hybrid engines.

One final but hugely important thing you can do is follow oil change intervals and use good quality oil. Testing shows how long a vehicle is likely to go before accelerated wear starts to happen.

Big Takeaways

I was a little surprised when I saw that there were such challenges, especially after knowing about the fleet of old hybrids out there (especially early examples of the Toyota Prius) that are racking up serious miles on the odometer. But, after learning more about designs, oils, and maintenance, this actually makes a lot of sense.

But, the challenges also show us the long-term things that will continue to make hybrids a poor substitute for an EV as long as we continue to improve charging opportunities!

Featured image: a screenshot from the embedded video (fair use).