How turbos & timing belts affect car reliability | Auto Expert John Cadogan

Let us bust a cap in the grilles of all you amateur engineers out there, painting by numbers and reducing complex issues to binary propositions because … the internet.
Welcome to another episode of What The FAQ - where you throw me the ball, and I come running back with it, enthusiastically, and then hump your leg (in the most platonic way, of course).
I’m John Cadogan director of dry humping outreach operations here at AutoExpert.com.au - the place where Aussie new car buyers save thousands on their next new cars. Hit me up on the website for that.
The online everything culture has a remarkable ability to disseminate uninformed opinion - and ordinary people get led up the wrong track on the hunt for some required automotive resolution. Here are some examples:
Warwick says:
I'm an elderly driver concerned with what seems to be the trend of dispensing with larger engines and replacing them with smaller turbocharged engines. I'm particularly wary of the merits of turbocharging for cars doing heavy stop/start city driving, particularly in relation to reliability issues. Now sure, I appreciate that it may well be that the turbo may not even operate in these cases and remains idle for long time periods but perhaps that in itself could be a problem? Is it something we need concern ourselves with? - Warwick
Marcelo says:
Do you know if the Hyundai i30 comes with a timing belt or a chain and how often does it need to be replaced?
And Ian says:
I’ve owned a 2009 Holden VE Ute from new and I’ve always had it serviced regularly by Holden dealers. Got the 150,000km service done last Saturday. The dealer’s diagnostic computer reported a timing chain problem. The Check Engine warning light went off but has reappeared today. Looking at online forums it appears that this is a known fault in this model. Some people suggest approaching Holden for a goodwill gesture in contributing to the cost of repair despite the car’s age as this should be a lifetime part. What should I do?
These are really common questions - belts versus chains (I get that all the time) and modern engine technology generally. So let’s deal with the specifics first and then the broader, bigger picture - because there’s a ‘forest for the trees’ visual scenario in play as well.
On turbocharging: There’s no real evidence smaller turbocharged engines are a reliability problem. (And I’m such a big fan of evidence.) Yes - turbocharging increases specific power output - so there’s more power per unit of swept engine displacement goodness.
But that idiot who said there’s no replacement for displacement? Obviously that was before forced induction and direct injection, and microprocessor control.
In fact, turbocharging saves considerable fuel by increasing thermal efficiency. So you get more power for each gram of fuel you burn. It also allows the engine to be smaller and therefore lighter (which delivers further efficiency-type savings).
Executive summary - turbo engines are more efficient and better to drive. They’re very well thought out, albeit a little more complex. There doesn’t seem to be profound negative feedback on this - the roadside littered with dead turbochargers.
On this issue of timing chains versus belts: They both do the same job, which would be precisely synchronising the cam and valve operation with the crankshaft - and this is tremendously fundamental to engine operation.
Belts typically are quieter and need to be replaced at some manufacturer-specified interval - like 100,000 kilometres. Chains don’t usually have a specified replacement interval - but they do wear out. And the principal wear characteristic is stretching.
When that happens, if the tensioner literally can no longer (literally) pick up the slack, the cam timing gets retarded, and the engine starts running like a dog. In Ian’s case, the car has done 150,000 kilometres. If the timing chain needs replacing that’s fair wear and tear.
You have to be reasonable: 150,000km is nearly four laps of the planet. Everything wears out. 150,000 is not an unreasonable life, and personally I think it’s a bit rich to allege that’s a fault. It’s actually just a consequence of that chain doing several million laps of the timing case…