There is a lot of anecdotal supposition (I have seen no actual evidence,) that the Ecoboost engine is more likely to suffer belt failure on lower usage cars.

WHY?

Most cars sit still most of the time so the oil drains off the belt when it is idle. If the engine is running then the belt is fully lubricated all over but the bottom sprocket is always immersed.

The nearest thing I can find to a theory is condensation within the block  causing acid buildup in the oil but I don't think so. Warming the engine regularly is always good for it but doesn't explain the phenmenon either.

The amount of tension on the belt which varies as the crank pulls the camshaft round to push the valves down is a constant between low and high mileage engines.

Is this a matter of owners getting in and thrashing the engine down to the station in the morning and back in the evening? Unlikely.

I reckon it is an Urban Myth. Six years and 60,000 miles in, often driven hard on long runs at three figure speeds for extended periods, all is well with mine so I wonder if anybody has another theory that stands up to examination.

I live in fear of wet belts (which idiot thought the concept and maintenance effort was a good idea!), ideally we'll never have one but they appear so common.
Rubber and oil usually don't mix.
How do you know "all is well" as you can't see inside?

I don't. Most Ecoboosts have not turned themselves inside out. As for

"How do you know "all is well" as you can't see inside? "

Who ever looks? on a dry belt car, there are covers that get removed at the service interval. Nobody inspects the belt routinely.

I can't see inside the clutch or gearbox either, so how do I know all is well? I don't.

From your initial post I thought you were looking for alternative theories (which I don't have)
IMHO it's just a bad idea as, based on the Baz Meredith etc videos, the oil pick ups being clogged with rubber particles and the state of the belts is dire.
Dry belts look almost perfect unless contaminated and it is often the idlers/water pump that fail.
You stated "all is well" but you don't actually know therefore all may not be well unless you change it?
Without knowing the details, it may be due for a change now?
Your operating regime theory  can be tested if the belt is in good order when it is taken out.
Based on my very limited knowledge it's better to change earlier as the risk is not worth taking.
We had a bad fuel filter (batch issue) which came to light when overtaking a lorry uphill and going into limp mode which could have been fatal therefore I change the fuel filter every two years rather than the recommended 3.
Whilst it is never totally black I'm not going to take that risk again.

Guess from working on them every day I DO get to see them, and can quite happily say that 90% of the belts I do that are either shedding, or worse gone completely are on low usage, low mileage cars. the mentality of people not using them very often and so skipping annual servicing (regardless of miles) being a factor. 

 

this could be debated all day long.  It is what it is.  if you live in fear of a wet belt and its costs, simply dont buy one.  its that simple. 

 

 

I worry about people who live in fear of them but don't have one! Skipped servicing is about the only reason for premature failure so you may have a point there. ("There's 5% left on the oil so it must be all right".)

No need to worry about me, I'll stick with Old Faithful and regular maintenance for as long as possible! 😉

As a low mileage user myself these days, it's something I ponder but can't say I'm having angst about it! I do think there's something in the theory of oil dilution/degredation through condensation on a little used engine.

Ste's comments on the correlation between low mileage and neglected servicing also hold water (no pun intended) imo. I have my wifes car serviced at the (very good) local garage, and often hear the lads there patiently explaining to other customers that components (particularly belts) still degrade through age even if they only drive a few hundred miles per year.

Strangely, on another current thread a Ford dealer appears not to have given this advice to the OP.

I still can't recall a thread on here where a car owned from new, and given at least annual oil changes, has suffered premature belt failure. 

Ford's recommended service intervals from the Mk 8 Fiesta onwards (2 years/18000 miles) are also not helpful imo. Yes, there is oil life monitoring FWIW, and tucked away in the service booklet is mention of the need for more frequent servicing in extreme conditions (including low mileage) but I wonder how many original owners spot that, let alone the 2nd or 3rd?

 

 

on the opposite side of neglected maintenance, I have a customer that changes his oil every 5k religiously. 

The car is a 2015 and had just over 80k at time of changing the belt and it was like new.  a few tiny particles in the pickup, but nothing serious. 

 

I did a 2015 focus with 18k miles last year and the belt was knackered. caught just in time. that had 3 oil changes in the 10 years the owner had it. (again they were going by mileage)

 

for those that dont know, the belt is under the most strain when starting and at idle. more common on low mileage cars doing a daily trip to the shop and straight back. 

 

theres always going to be conflicting opinions on why some fail more than others.  Anyone purchasing one of these cars with these engines MUST factor in the additional cost for doing the belt early, or buying one thats had the belt done recently. 

 

the costs boil down to whether you value ford dealer stamps in your book, or a good reputable and experienced garage.  As discussed before I charge £1200 inc all materials and labour if there is no issues in dismantling and refitting.  £1300 if the flexi needs replaced. 

compare that to a dealer price locally of 2k, you see where the true problem lies. ££££

 

 

Personally I think that Petrol contamination is greater in cars that are only used for short journeys and it is less likely to get burned off because the Oil does not get hot enough. You can often smell the Petrol when you remove the Oil Dipstick in a short journey only car.

I don't have any scientific evidence that says Petrol contaminated Oil is bad for a Belt, just my own thoughts. 

More grist to the mill:
https://www.youtube.com/watch?v=pjYPn_DU8uw

Do you feel lucky, Punk?

Edit: This is a general joke comment and not directed at anyone. Owners need to be aware and change the belt at least as often recommended and consider earlier (I think other times are suggested by members on here.)

"The belt is under the most strain when starting and at idle." 

 No. I disagree. Show your working.

AI Overview

Yes, a timing belt is under 
strain when the engine is cranking. Cranking the engine involves significant mechanical resistance as the crankshaft turns, which in turn forces the timing belt to drive the camshafts and operate the valves and pistons in a synchronized manner. 
Here is why the timing belt is under strain during cranking:
Mechanical Resistance The process of initiating combustion requires overcoming the compression of the air/fuel mixture in the cylinders, which creates substantial resistance on the pistons and crankshaft.
Power Transfer The starter motor applies torque to the crankshaft, and that force is transmitted via the timing belt to the camshafts to open and close the valves at the correct time. The belt must maintain tension and grip the gears to ensure precise engine timing.
Tensioner Operation The timing belt tensioner manages the slack in the belt, ensuring proper tension is maintained across the entire system, even during the initial, high-load cranking phase.
Potential for Failure If a timing belt is worn or stretched, it may struggle to turn the components at the correct speed during cranking, leading to an engine that is difficult to start or won't start at all. In extreme cases of wear, the teeth may strip, or the belt may snap entirely during this high-stress operation. 
Therefore, the timing belt is actively working and under strain during the cranking process. 

save myself the bother of typing an explaination. ha

 

Saved yourself the bother of thinking by posting something that refutes what you said without reading it. It is under strain, agreed but not MOST strain. It isn't.

As for the belt not turning at the correct speed, the AI bot which wrote this poppycock failed GCSE science, as the rest of us have already worked out.

Now go back and read it or suffer a mathematical explanation from a human who does understand physics.

I changed my belt at 10 years, 38,000 miles, with lots of short runs during that time. The belt was in good condition at the time of replacement. The car was serviced on time every time, witch i beleve is the key to longevity for wetbelts. I can post a picture of the old belt if anybody wishes to see it.