Engine longevity - safedriver
I am thinking of changing my Peugeot 307 for a Prius as most of my driving is at low spees around the outskirts of London with occasional (approx monthly) squirts down the M4 or M3 to Wales or SW England.

My only real concern is that HJ continually tells people not to turn the engine on for very short periods as this reduces considerably the engines longevity. I suspect that if I drove a Prius, the engine would fire up for less than a minute several times on a journey. Would this not encourage internal corrosion?

Anybody know?
Engine longevity - cheddar
I am anti Prius on principal, hypocritical marketing claims, better of with a diesel Auris/Focus/3 Series in the real world, though to the answer to you question is surely to change it before the warranty runs out.
Engine longevity - safedriver
I don't think I do a high enough mileage to justify a diesel. I think my choice will be between Civic/Focus/Prius.

I wonder, though, about condensation from a cold engine damaging the exhaust. I might not be buying new depending on whatever deals are around and if I do I hope to keep my next car for many years, possibly longer than the warranty.

It's not the green credentials of the car which I find attractive as the 70 mpg combined cycle figure.
Engine longevity - nortones2
The 70mpg figure is almost certainly even more optimistic than for a conventional engine. I suspected as such when the Lexus hybrid claimed >40mpg on the urban cycle. According to Auto Express, present rather dated test methods "allow" (because they are not expressly forbidden!) hybrid makers to overide the conservative battery charge settings. Thus, the batteries are fully charged, rather than 80% max, and fully discharged rather than keep to a 20% reserve. Et voila, a mileage figure of wonderful promise. Shame the road tests show an even bigger discrepancy than normal.

As for diesels as an alternative, not everyone wants one. Given the Prius has an automatic transmission, it could be a good choice for mainly urban usage with good fuel consumption if not stellar. Try it and see if it suits, is my view. BTW, the Auris has manual plus an automated manual auto offering: HJ slates it.
Engine longevity - TheOilBurner
The Prius doesn't use a traditional Otto cycle petrol engine. Instead it uses an Atkinson cycle unit. Given that the engine was specifically designed for the Prius, I doubt there would be any problems with its usage.

However, I'm in agreement for Chedder, what is the Prius going to do for you that a diesel Auris couldn't?

I would also expect that the engine might come on more often than you might expect, after all, that battery needs re-charging.
Engine longevity - craig-pd130
Surely short / slow journeys would be just as detrimental to the life of a diesel motor?

Also, if there's a lot of low-speed, short distance work, there's the DPF factor to consider, too.

A caveat is, my Mondeo IV has a DPF and often goes 2-3 weeks without going over 50mph or further than 6-7 miles per journey, and I've had no DPF problems in 17,000 miles ... but if there's one thing the Back Room tells us, it's that your mileage may vary ....

Edited by Dynamic Dave on 19/10/2009 at 20:09

Engine longevity - cheddar
Surely short / slow journeys would be just as detrimental to the life of a
diesel motor?

Yes but the diesel engine will run all of the time the car is being used.

Edited by Dynamic Dave on 19/10/2009 at 20:10

Engine longevity - craig-pd130

I was trying to be grammatically correct too :-D

Also, to answer another point from the OP, I can't see a Prius giving 70mpg in the real world. If it does, I'll be queuing for a test drive ...
Engine longevity - safedriver
Also to answer another point from the OP I can't see a Prius giving 70mpg
in the real world. If it does I'll be queuing for a test drive ...

I'd be happy with 50mpg in town, to be fair. I currently get about 33mpg from my 1.6 auto 307.
Engine longevity - safedriver
I would also expect that the engine might come on more often than you might
expect after all that battery needs re-charging.

That's true. Most of my journeys are less than 10 miles in urban areas (my 307 trip computer never gets reset and shows an average speed of 23 mph - and that includes long trips on motorways). The Prius needs plug-in ability. Free motoring by plugging in at work!
Engine longevity - Statistical outlier
Mainly urban use is one of the only places where a hybrid makes perfect sense in my view.

Urban driving is incredibly hard on the two components in a modern diesel that are very expensive to fix - the DMF and the DPF. In constant stop-start traffic an auto is the way to go, and a hybrid actually makes some gain out of this type of use.

Motorways and high mileage - diesel
General lower mileage use - petrol
Mostly urban - I'd look at a hybrid.
Engine longevity - TheOilBurner
Absolutely, I'm not sure why Toyota are delaying the plug-in option, because the car truly makes sense when that is added. Without it, its in the balance IMO.
Engine longevity - cheddar

I only mentioned Auris v Prius so as to not be percieved as anti Toyota, a VW TSi petrol migh be worth looking at.

Engine longevity - Chris23
I would be much more worried about the life of the battery pack.

I suspect that when it goes the car is not worth repairing.

Engine longevity - ifithelps
...traditional Otto cycle petrol engine. Instead it uses an Atkinson cycle unit...

Er, aren't they all just four strokes?

I'd be grateful if OilBurner, who posted the above, or anyone else, could explain what difference is between the two cycles.

Engine longevity - b308
Its not just the mileage... many companies offer the diesel for the same price as a petrol... and waaaay cheaper than a Prius (which is overpriced)... if you are looking at same priced petrol/diesel then it comes down to whether you can live with the extra noise in a diesel for the 20/25% gain in fuel economy... I can...
Engine longevity - TheOilBurner
I'd be grateful if OilBurner, who posted the above, or anyone else, could explain what difference is between the two cycles.

Of course...

To quote from About.com:

"Invented by British engineer James Atkinson, the Atkinson Cycle is one in which the stroke of the piston can vary in length across the four cycles in a four-stroke internal combustion engine. Typically, the length of the stroke during the power cycle is increased to promote efficiency; however, because this can come at the expense of a shorter intake stroke, there is some loss of power?for this reason, this type of engine design is best suited for use in a hybrid system where the electric motor can compensate for these power losses."

Clear? ;)

There is no particular reason I know of why an Atkinson cycle ICE would be more suited to on/off usage, however, I'm sure Toyota would have taken this into account in some way. Perhaps there are other ways in which a hybrid is better for avoiding damage whilst cold, i.e. no idling when cold and unlikely to suffer high revs too.

So all in all, the differences may help it balance out.

Now I'm hoping someone will real brains like Number Cruncher can come and clarify all that!

Edited by TheOilBurner on 19/10/2009 at 17:43

Engine longevity - cheddar
>>Now I'm hoping>>

I belive that the Prius achieves a virtual Atkinson cycle via variable valve timing.

Engine longevity - Roly93
>>Now I'm hoping>>
I belive that the Prius achieves a virtual Atkinson cycle via variable valve timing.

Yes, like Miller cycle but without the usual supercharger.
Engine longevity - ifithelps
... the Atkinson Cycle is one in which the stroke of the piston can vary in length across the four cycles in a four-stroke internal combustion engine...

I'm sure I'm missing something here....

Surely, the length of the stroke of the piston cannot vary 'across the four cycles' because the piston is firmly connected to a con rod which in turn is bolted to the crankshaft.

The piston travels up and down the bore for the same length each time.

Must have been a clever fella this Atkinson, cleverer than me, at any rate.

Engine longevity - Statistical outlier
IIH, you're exactly right, an Atkinson Engine is a normal 4 stroke engine with a different linkage between piston and crank.

See www.animatedengines.com/atkinson.shtml as an example.

However, the illustration shows the engine with the linkage laid out to generate 4 equal strokes. To alter the ratio of the strokes, the rightmost pivot point (the one that is attaching the horizontal green link to the frame) should be moved downwards along the frame. This will allow more angular movement as the link rotates up, giving a longer piston stroke for power and exhaust, and less angular movement as the link rotates down, giving a shorter piston stroke for intake and compression. In fact, a sliding pivot point at that location would allow the engine to dynamically change the stroke ratios. (Quoted from Allexperts.com)

Edited by Gordon M on 19/10/2009 at 19:59

Engine longevity - ifithelps
See www.animatedengines.com/atkinson.shtml as an example.

Gordon M

All is now much clearer - thanks for posting the link.

Engine longevity - cheddar
IIH you're exactly right an Atkinson Engine is a normal 4 stroke engine with a
different linkage between piston and crank.
See www.animatedengines.com/atkinson.shtml as an example.

Though the Prius is not Atkinson, rather as I said it achieves a virtual Atkinson cycle via variable valve timing.
Engine longevity - KMO
Second-hand battery packs are readily available, because they fail far less often than Priuses get mechanically written off in accidents, and don't usually get damaged in such accidents.

Compare to a typical automatic transmission, which fails more often, nominally costs just as much from the manufacturer, and is far harder to obtain and fit from scrap...

Silly to poke the Prius for the expensive bits it has, when there are plenty of expensive bits it avoids.
Engine longevity - KMO
The Prius babies the engine quite a lot - the computers have full control of when and whether it runs, and at what RPMs. They take advantage of this to minimise emissions and wear+tear.

At start-up the motor runs continuously for a while, with a rich mixture, until the catalytic converter and other bits are up to temperature. During that period, you get most of your drive from the electric motor+battery - the engine idles if possible. (But if you floor it, it will rev up to give you power). After that, it runs as necessary for power, or to maintain engine temperature, or cabin temperature.

The stopping and starting of the engine are governed by the electric motor - it can spin the engine up to full operating speed before fuel is injected, so there's no particular stress on the engine (or the passengers).

The Prius is ideal for pootling around town. My two Mark IIs have done almost entirely that, with occasional long runs, and have averaged over 50mpg in their lifetimes (calculated manually, not taken from the slightly optimistic trip computer).

And it's not a question of firing up for "less than a minute" - sometimes the motor will come on only for a burst of power for a few seconds.
Engine longevity - Bagpuss
The German motoring magazine Auto, Motor & Sport did a long term test of the Prius about 3 years ago. In 18 months they managed to do over 100,000km (which makes the long term tests in Top Gear look decidedly girly). They then did what they always do to their long term test victims vehicles, they took it to pieces and looked at the amount of wear. Basically, there was none. There was no noticeable wear in the engine or transmission components, and no rust (unlike the long term Auris, but that's another story).

The Prius was designed for the USA where short journeys and start/ stop urban traffic is the norm. I think they've got the concept pretty well sorted. I think the main disadvantage the Prius has as urban transport is the fact that it's too big for European urban transport. I wouldn't worry about the engine or transmission.
Engine longevity - boxsterboy
A lot of those Auto Motor & Sport strip-downs show little wear, but then they are doing high mileage in short time (mostly on the autobahn?) which is better for engine wear.

You won't get 70 mpg from any car (except maybe a G-Wiz) in the OP's use. If I were him and happy with 50 mpg I would look at a pre-reg Focus 1.6 TDCI for under £10k, saving £7k on a new Prius and enjoy similar consumption.
Engine longevity - frazerjp
My Dad's new Prius III with recent mixed driving, the trip computer shows around 62 mpg, so reality we're talking about higher 50's.
Engine longevity - kiss (keep it simple)
I read a report from an American fleet test of the Prius and a big saving came from reduced pad and disc wear due to the regenerative braking. I mentioned this to a taxi driver in Glasgow and he said brake replacements were one of his biggest expenses.
Engine longevity - Kiwi Gary
In my Prius experience, admittedly only some 95000 miles, there are many conditions when the engine doesn't actually cease revolving even though the fuel flow meter shows infinite mpg. The computer must sense when you are in a situation where power demand is changing relatively often, and keeps the engine ticking over but at such low fuel consumption that ther flow meter doesn't register it. Example - to get to the motorway, I drive about 8 miles over undulating roads of about 200 yards up followed by the same down. The engine keeps running at tickover on the downs, only stopping when I stop for traffic lights.

Just another note, as you are coming into Winter - if the outside temperature drops to 3 deg or less, the engine is kept running anyway. I queried Toyota on this, and it is to keep the cat up to temperature, and also to help keep the cabin habitable. A yellow symbol looking a bit like an inebriated snowflake comes up on the dash to inform you that the engine will run continuously.
Engine longevity - diddy1234
Kiwi Gary, so in the dead of winter the prius is useless for its eco ability in town then.

May as well just buy a diesel car for a cheaper price.

Sorry to sound so negative, I really don't mean to but I thought the main advantage of the prius was in stop start driving (traffic) as the engine would turn on and off when needed.
Engine longevity - MVP
Don't be too hard on the Prius - Rome wasn't built in a day, and at least Toyota are trying new technologies.

Engine longevity - Statistical outlier
Diddy, you're being overly simplistic in your thinking.

Sure, in winter a Prius may need to keep the engine running, but probably only at idle for a lot of the time. While it is idling, it's putting charge into the battery, so when you move off again, the electric motor can do 90% of the work. When you slow down again, the regenerative braking puts charge back into the battery again rather than the kinetic energy being 100% wasted.

The net effect is that while the motor may be on all the time, it can be running at minimum power output for a lot of the time, and more of that power generated can be saved and used to provide motion, so it's more efficient.

I'm generally not a fan of the Prius, but I think they make a huge amount of sense as a London car - London driving is horribly hard on a normal Diesel.
Engine longevity - nortones2
As GordonM says! Remember that the electric motors (two) and the ICE work together, so the amount of reliance on the ICE is reduced. If the Prius does 50mpg in town , there are few vehicles of that size that could match it. I don't know how much is saved by the ICE switching off at the lights, maybe 5%?

Edited by nortones2 on 20/10/2009 at 11:21

Engine longevity - mustangman
Just to add "grist to the mill" Others have mentioned the possibility of a Tsi VW.

I've been running a 1.4 tsi, dsg Golf for about 6 months.

I get a minimum of 40 mpg on short urban runs, around 42 average and up to 50 or above on longish trips with much cruising at reasonable speeds.

I chose this engine since it has chain cam drive, and obviously no DMF or DPF. The engine does have variable valve timing and direct injection however.

I'm very happy with it, bar for some transmission snatching at low speeds if you are not carefull.
Engine longevity - boxsterboy
Mustangman, that's exactly the consumption I get from my 7-seat 2.0 HDI C4 Grand Picasso with the EGS box. Even your comments about the transmission snatching at low speeds if you are careless apply!
Engine longevity - David Villa
I think you just have to look at recent reliability surveys that put the prius(admittedly previous version) at the top of the family car sector.

The prius has been around for many years and initial doom and gloom merchants' claims about unreliability and the battery packs breaking down or wearing out have proved totally unwarranted.

In fact the battery packs are one of the most reliable part of the car with Toyota/Lexus having hardly ever had to replace them even in the original mark 1 prius.

Nice to see there are still doom and gloom merchants around wanting us to inhale lovely black smelly diesel exhaust particulates and the rest of it.Amazing how zealous and vehement they are.
Engine longevity - T Lucas
I want a Honda Clarity,sounds like the way forward.
Engine longevity - diddy1234
MDI and their compressed air cars is another way forward.

No problem with refilling in minutes or plugging into the mains for 4 hour refill !

Edited by diddy1234 on 21/10/2009 at 13:45

Engine longevity - safedriver
I just want to say thanks for all of the replies. Every one was helpful and informative.

I think I'll probably go for a Focus petrol auto.

Most of my journeys are short, and my annual mileage is low, so I will stick with petrol. I am only expecting to buy about £1,000 worth of petrol so the extra cost of a nearly new Prius will take many years to recoup in petrol savings (and I suspect that a similar argument could be made for carbon savings). I also like to use independent garage servicing, and feel that this will be less expensive for a Focus.

Thanks again for everyone's help.