Big engines last longer - truth or myth?!!

[B19GRR]

Due to the evils of the bargain barge thread ensnaring me with the mad urge to own a vast road going blimp for minimal outlay, it's got me wondering about the whole idea of larger displacement engines being good for many hundreds of thousands of miles. For example, there's an '88 750iL on fleabay, seller didn't put mileage in the add (why do they do that?!!) so I asked and got this reply:

"hi rob,there is no service history and mileage is around 180,000 low mileage for a V12. regards"

Now how can anyone really justify 180k being low miles for any engine, especially one with unknown history? As far as I'm concerned the pistons in a V12 will all have gone up and down just as many times as those in a weedy 1.0l 4 pot (assuming - rashly - the same gearing) to cover the same distance. The V12 has a longer crank - hopefully with a couple more bearings mind - so higher risk of flex, and it's got way more gubbins in the two heads than the 4 pot to wear out.

So can anyone think of any reason why a 4 pot shouldn't last just as long as a bigger engine?

BTW this is not a rant, please note conspicuous absence of angry smilies, none of the above blah is putting me off getting a big engine!!

Cheers,
Rob

[Strawman]

B19GRR said:

"hi rob,there is no service history and mileage is around 180,000 low mileage for a V12. regards"

There is some truth to the big displacement / low compression = less wear, but I think the quality of construction and the level of maintenance an engine receives has more to do with how long it lasts, plus the use it is put to, so lots of motorway miles is easier on an engine than many short trips.
There is a (old 900) Saab engine out there with 1,000,000 miles without a rebuild (lowly turbocharged four pot ) and many better built engines can get to 250,000 without needing major attention, don't know about the BMW V12.

[stuartbuckell]

Gazboy said:

I'd say it's more related to specific output, compression ratios and how it was built. You simply wouldn't expect a 230bhp K-series 1.8 to last 50k, yet you would be truley hacked off if a LS7 gave up the ghost after double that.

That's why the old Pug Diesels (405/406) go on forever and ever. Low power output (ish), is reliability.

The more power, the more strain.

A 500 BHP V10 5.0 BMW engine might not last as long as a good old American 5.0 v8 putting out 150 bhp.

But, that could be complete crap if the BMW engine was built to excellent tolerances with top quality parts, and the American engine was some GM crap with cheap parts ...

If the car has had motorway miles, rather than short distances, and good levels of servicing, they should go on forever.

My old man told me a story once about a Ford dealership he worked for when he was in his 20's. They sold engines to a petroleum company who tested fuels, and sold a LOT of engines to them. Funny thing was, over half the engines came back, as they were taken apart and found to be way outside Fords tolerances specified when being built (I'm guessing pre-robotics/cnc machining, this is the 70's).

The perfect Ford engines were run day and night. They estimate around 300k miles on the engines that lasted and were built within tolerances. Funny thing was, those engines were better than the new engines, and produced more power/more reliable. The staff tried to nick those engines and put them in their cortinas

So I guess it comes down to the quality of the engine, how well it was made/parts, and the life it's had. 40k miles of local trips will probably be worse than 100k miles of motorway. There is no definite answer for a majority of major manufacturers.

[Dracoro]

stuartbuckell said:

That's why the old Pug Diesels (405/406) go on forever and ever. Low power output (ish), is reliability.

The more power, the more strain.

Try telling that to Honda How to make high power AND reliability.

But yes, granted, the statement is true for most cars IMO. Although some larger engined cars are in the sportier models which inherently get driven harder negating the low workload on the engine.

The bigger engine will have to work less hard than a small one in the equivalent car. Yes each piston will have to go up and down like in a car with less cylinders, however they don't have to go up and down as fast or as much to propell the car down the road.

I would expect a BMW 4.4V8 to last better than a 3.0 V8 in, say, a 7 series or SUV size car.

[stuartbuckell]

Dracoro said:

stuartbuckell said:

That's why the old Pug Diesels (405/406) go on forever and ever. Low power output (ish), is reliability.

The more power, the more strain.

Try telling that to Honda How to make high power AND reliability.

How many Civic Type-R/S2000 engines do 250,000 miles before a rebuild?

[Dracoro]

Probably more than any other manufacturer. However CTR/S2000s are sports cars and sports cars in general don't do high mileages but if they did I suspect they'll put up with high mileage better than most.

[Simond001]

Dracoro said:

stuartbuckell said:

That's why the old Pug Diesels (405/406) go on forever and ever. Low power output (ish), is reliability.

The more power, the more strain.

I would expect a BMW 4.4V8 to last better than a 3.0 V8 in, say, a 7 series or SUV size car.

I wouldnt. 4.4 V8 from BMW one of the worst engines made. Liners fall apart at anything betwen 8,000 and 90,000 miles.

Most dealerships kept a spare for when a 7 series came in on the back of a low loader.


In general a large displacement engine should last longer than a small displacement engine producing the same power. BMW's Nikasil issue http://www.bmw-board.co.uk/nikasil.htm is ongoing. also affect some Jaguars.

[10 Pence Short]

stuartbuckell said:

Dracoro said:

stuartbuckell said:

That's why the old Pug Diesels (405/406) go on forever and ever. Low power output (ish), is reliability.

The more power, the more strain.

Try telling that to Honda How to make high power AND reliability.

How many Civic Type-R/S2000 engines do 250,000 miles before a rebuild?

I did 125,000 hard miles in 23 months in my old Civic Type-R. Everything but the engine broke at some time or other.

My old 1.8 Accord was last seen running absolutely spot on with more than 230,000 miles on the clock.

The replacement Accord 2.4 is still going at 150,000 miles plus.

[paulsm]

engine may be fine, but what about suspension, steering, etc etc etc

[tinman0]

B19GRR said:

Now how can anyone really justify 180k being low miles for any engine, especially one with unknown history? As far as I'm concerned the pistons in a V12 will all have gone up and down just as many times as those in a weedy 1.0l 4 pot (assuming - rashly - the same gearing) to cover the same distance. The V12 has a longer crank - hopefully with a couple more bearings mind - so higher risk of flex, and it's got way more gubbins in the two heads than the 4 pot to wear out.

a 1.8 or 2.0 will probably be geared differently so the engine over those miles will of done more work, whereas a V12 5.0 will be much less rpm, and so not turning quite as hard.

(eg my Golf Mk2 GTI 16v = 5,000@100 vs Mustang GT 4.6 = 2,900@100)

isn't there also something where not all 8 cylinders fire for 1 rpm?

personally, it wouldn't be the engine putting me off a 750i, it'll be the running costs, and the electrical bits that go wrong. reckon it could turn into the fourth bridge if you're not careful.

but stuff all that, buy it and see what happens! you'll only regret not buying it when your 80

[kambites]

tinman0 said:

isn't there also something where not all 8 cylinders fire for 1 rpm?

On a 4-stroke engine each cylinder fires once every, um, 4 strokes (revolutions of the crank shaft).

OK a few very modern engines shut down certain cylinders when they aren't needed but that's pretty rare.

[munky]

Dracoro said:

Probably more than any other manufacturer. However CTR/S2000s are sports cars and sports cars in general don't do high mileages but if they did I suspect they'll put up with high mileage better than most.

Depends on your definition of a sports car.

[Dracoro]

paulsm said:

engine may be fine, but what about suspension, steering, etc etc etc

Precisely, many luxobarges have loads of complicated supension, not cheap to replace and being a heavy car wears them that much more.

Anyway, on most cars, as long as it's oiled, the engine is quite often the last thing to go. I'll wager there's lots of dead cars in scrappies where the engines are more than OK, just the rest of the car that's had it

[SJobson]

Simond001 said:

Dracoro said:

stuartbuckell said:

That's why the old Pug Diesels (405/406) go on forever and ever. Low power output (ish), is reliability.

The more power, the more strain.

I would expect a BMW 4.4V8 to last better than a 3.0 V8 in, say, a 7 series or SUV size car.

I wouldnt. 4.4 V8 from BMW one of the worst engines made. Liners fall apart at anything betwen 8,000 and 90,000 miles.

Most dealerships kept a spare for when a 7 series came in on the back of a low loader.


In general a large displacement engine should last longer than a small displacement engine producing the same power. BMW's Nikasil issue http://www.bmw-board.co.uk/nikasil.htm is ongoing. also affect some Jaguars.

??? Nikasil wasn't used in the 4.4 V8, and BMW put that in the 8-series, 5-series, 7-series and X5 for years without any such difficulties. My own E39 540i has done 131,000 miles without the liners falling apart.

Good to see you contradicting yourself by stating that you would expect a bigger engine to last longer anyway. You do know that the 4.4 V8 and the 3.0 V8 are basically very similar, though the 3.0 is the one with Nikasil, being the older M60?

Back on topic, I think the gearing and torque does play a major part in it. My 540 rarely exceeds 2000rpm when pootling around. The overall gearing's a fair bit higher than, say, a Civic Type R, but the fact that it'll pull from well under 1000rpm means that it's also a gear or two higher in most circumstances. So each piston is stroking the bore less often than in the smaller engined car, and at a lower speed while doing so.

[EDLT]

Do revvy small engines need more attention than big lazy engines?
I wonder how long a Clio 197 engine will last...