Car mpg question

And worst of all, the diesel clatter.

That is something that has massively improved in recent models, years ago Toyota diesels were almost as quiet as petrol engines, it has taken about twenty years for the rest to catch up.

Modern diesels don't clatter. They not as quiet at idle as most petrol engines but they're pretty well tamed now.

Tim

Tim+ laid this down on his screen :

No clatter from mine. On the road it is almost silent, the car is very well insulated from noise. At tick-over and cold, there is a very slight clatter. What clatter there is suddenly stops within a couple of minutes - I guess something changes mode in the engine ECU.

in the old days cold starting included mechanical pump advance which tended to make diesels more clattery, modern ones do the same, but electronically. On old escort diesels it was often necessary to advance the pump a bit to get them to run more smoothly from cold, had to do the same on an Alfa (?) diesel too.

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But you do notice a diesel; there is no hiding from that.

4-cyl petrol engines have also improved with clever balance shafts, moving the goalposts.

Petrols have also improved, moving the goalpost. To sum up: Dielsels are noisy and polluting if not well maintained. Repais are expensive.

But... Diesels seem the only option for big commercial vehicles: Super vans and lorries. It makes me wonder how diesels fare in such heavy duty applications. Extensive mileages, extensive work load.

What is the mgp for the big lorries? mpg per vehicle weight? How many miles do they make on an engine?

big stuff around 6mpg and an engine will do 500,000 upwards.

With modern cars it is hard to immediately tell from the driving seat or passenger seat whether it is petrol or diesel.

How many car engines use balancer shafts though? Do Saabs still use them? Does anyone else?

Tim

Saab is no longer in existence. Saab used balancer shafts on the 2.3 and also on 2.0 from MY 1994. The Saab solution did something special do dampen even more vibrations which earned Saab an award for 10 best engines (Wiki). This old Saab 9000 4-cyl engine is really exceptionally smooth. It makes you think that performance is not just about jacking up the bhp to some insane levels, it's also about refinement of engine.

SAAB went to the wall about 5 years ago and had been using GM engines for 10 years before that. The GM 2.0 and 2.2 Ecotec engines have balance shafts.

Probably not an exhaustive list.

It is only large 4 cylinder engines that use balance shafts. Large being about 2.0L to 2.4L. For "truck" (aka SUV) applications they wouldn't bother. For cars aimed at luxury market they would fit them on 2.0L.

Even fairly small 3 cylinder engines use them - run at engine speed as the out of balance is end to end rocking couple. This engine speed out of balance is far more objectionable than the 2x engine speed out of balance of an in-line 4. Higher frequencies are easier to damp with engine mounts.

Jag AJ126 V6 derived from a V8 has a balance shaft.

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There are probably more cars with some sort of balancer system on the road now than ever before - pretty much all the 3-cylinder ones, including BMW's B38 series.

Ford get around the balancing issues of 3 cylinders on their 1 litre Ecoboost by making the crankshaft and crank pulley asymmetrically balanced.

Chris

the only ones I have come across have been on Hondas

They fare fine with a limited rev range and lots of gears. You do not want haulage firms storing that about of petrol instead.

The Saab 9-5 was produced until 2010, it used the B205 or B235 original Saab engines. Only GM derived engines for 9-5 were the Saab 6 cyl models, but not as powerfull as the 4-cyl full turbo 2.3L.