I have a four-year-old Hyundai Kona I bought from a private seller with 40,000 miles on the clock and the engine has just blown up.

The car has a full service history by Hyundai but the manufacturer has refused to replace the engine under warranty on the basis that servicing has been carried out several thousand miles later than the recommended intervals.

I had been assured by the dealer who serviced the car for the first owner that it had a full service record. Now Hyundai is trying to charge me thousands of pounds to cover the cost of a replacement engine.

I think it's unfair that they are trying to wriggle out of their five-year warranty commitment using this stipulation, especially when a major component has failed so early in the car's life. D.D

Rob Hull, MailOnline & This is Money Motoring Editor, replies: When searching for a second-hand car of any age, one listed with a manufacturer's full service history will be desirable as it suggests it has been maintained with expertise and parts supplied by the company that built it in the first place.

But seeing the three letters 'FSH' isn't enough to guarantee a car has been maintained to the highest possible standard in the eyes of the car maker no matter if it's a two-year-old vehicle or one that's been on the road for fifteen years.

Service intervals typically tend to be every 12 months or 12,000 miles, whichever comes first. However, this can differ by brand and model, so check the owner's manual.

Intervals are scheduled around when parts and components usually start to show signs of wear and tear - as well as time-related degradation - and therefore need to be inspected and replaced where necessary. 

There are three different types of service. The first is 'interim', which is usually only for excessive mileage drivers, leaving two main types: 'full' and 'major'. The latter includes additional checks on top of a full service as part of a more thorough assessment of the condition of the vehicle. 

These are staggered because more durable parts don't require inspecting, refreshing or replacing as often as others.

Adhering to these recommended intervals - in theory - reduces the risk of breakdowns and component failures that could turn dangerous. It also means worn-down consumables, like brake pads and discs, and tyres are replaced when they need to be.

A full service history still might have a hidden issue 

Cars that have been consistently late to be serviced could have experienced excessive wear and tear on components. This could then have a knock-on impact and cause future problems further down the line.

Manufacturers know this, so they protect themselves from costly repair claims by requiring service intervals to be strictly adhered to as to not invalidate warranties - which cover vehicles typically for the first three to ten years (with mileage limitations included) depending on the brand.

Therefore, even a car with a 'full service history' might still have invalidated its warranty requirements if it has been 'excessively' late for at least one of these services in its lifetime.

It means used car buyers need to closely scrutinise the service book and all accompanying paperwork to understand if intervals have been met. Each service stamp should include a mileage record in a car's service book.

In D.D's case, they have failed to check the service record thoroughly.

Had they done so, they would have discovered that every service has been well behind the intervals.

For a petrol Hyundai Kona, the intervals are 12 months or 10,000 miles, depending on which occurs first.

D.D's car missed the original interval by 2,700 miles, the second by almost 6,850 miles and the third by nearly 2,600 miles. That tallies up to 12,150 miles over schedule, which is in excess of a service interval.

Because of this, Hyundai has refused the claim to cover the cost of a new engine.

Where I sympathise with D.D is that it isn't always made clear what the acceptable late window is for a warranty to be deemed invalid.

And it seems there isn't an industry standard for this, meaning manufacturers are setting their own rules... 

When is a late car service too late? It depends on the brand...

I contacted 30 of Britain's most popular car brands to find out what is their acceptable threshold for a vehicle to be late for a service to guarantee the warranty remains in place.

What I received was a raft of very conflicting requirements. 

The general rule of thumb appears to be that service intervals need to be adhered to within 1,000 miles or one month (or 30 days) of the manufacturer's recommendation.

But not all go by this tolerance level - and there are many, many grey areas.

For instance, BMW refused to give us a mileage or time window in which a late service would not invalidate the warranty. Instead, it said drivers will be 'notified by the car's intelligent maintenance system' with alerts on the screen when a service is due.

It then states: 'If a vehicle develops a faulty component and that component may have been affected due to service recommendations not being followed, then the warranty claim may be rejected.'

Dacia quotes a 30-day, 1,000-mile interval window allowance. However, it then caveated this by saying that if a service is missed or 'completed outside the required intervals, e.g completed six months late or 5,000 miles over, there is a possibility that, if the issue identified is due to the late service, the warranty may be invalid for that specific issue'. 

However, it added that this 'will not affect the vehicle's warranty as a whole - for example, parts not linked to a service will still be covered under warranty'. 

Honda's reply was even less conclusive. A spokesperson told us: 'There is no specific window stated, however, Honda would need to review on a case-by-case basis.' 

Mazda said it allows for a 1,000 miles or one-month leniency, though openly admitted that 'this is not mentioned in customer literature'. Yet, it still expects owners to 'present vehicles for servicing at the right mileage or time, whichever occurs first'. 

MG allows for a 1,000-mile grace period or just 28 days. 

Toyota says that if there is a claim made for a mechanical failure due to a service-related part, the car must have the correct number of services relative to the vehicle's mileage and it will allow a variance of up to 1,000 miles or two months against each interval. 

Confused yet? I know I am! 

The mainstream manufacturers with the most lenient rules include Kia, Mercedes-Benz and Stellantis Group brands.

Kia told us it has a three-month or 1,000 mile grace period. 

Mercedes' window for acceptable lateness to retain the warranty is 3,000km (1,864 miles) or up to 90 days after the recommended service date. 

Stellantis, which owns Alfa Romeo, Citroen, Fiat, Peugeot and Vauxhall, won't invalidate your warranty as long as you have the car serviced within three months or 3,000km (though it stipulates a 1,800 mile conversion) of the indicated interval.  

Whereas electric car maker Tesla says it has no required service intervals whatsoever.

At the opposite end of the spectrum is Volkswagen Group - which oversees VW, Audi, Cupra, Skoda, Seat. 

A spokesperson told us that it does not allow for a 'grace period' at all, saying it 'would expect the specified time/mileage parameters to be adhered to in order for any warranty claims to be honoured'.

*Scroll to the bottom of this story to find the full list of manufacturers, their warranty lengths and grace periods for service interval lateness 

Lawrence Whittaker, CEO at extended warranty provider at Warrantywise, replies: It is a prerequisite of most car warranties that as the owner of the vehicle you must keep the car serviced in line with manufacturer's recommendations. 

It is unfortunate that this service schedule was missed by the previous keeper and was likely unbeknown to the current owner. 

However, it is the current owner's responsibility to check previous service history carefully, especially with cars like Hyundai that come with a longer five-year warranty to ensure they don't get caught out. 

With the average annual mileage in the UK being around 7,400 miles per annum, being thousands of miles past a service schedule is quite a long time and I think Hyundai are within their rights to decline this claim.

If the owner purchased the car from a dealer within the last six months, they might have some redress under the Consumer Rights Act. 

Warrantywise understands that sometimes schedules and workshop availability don't always align, so we allow for up to 1,000 miles or 30 days either side of the service period. 

We also allow new owners who do not know the previous service history of their vehicle to bring the car up to standard, so they can still enjoy Warrantywise cover.

What Hyundai said about DD's case

When we contacted Hyundai about its service interval tolerances to retain the warranty, it said it would allow for lateness up to 1,000 miles or 30 days.

In DD's case, one of the late services was almost seven times that mileage threshold. 

The Korean car firm says that if failing items (in this case the engine) are service related, then it will 'need to be established if this is as a result of a late service before anything is deemed invalid'. 

It added: 'In exceptional circumstances, Hyundai will support a customer as required.'

Hyundai diagnosed DD's car's engine failure to be related to a 'lack of oil viscosity properties, due to a combination of low levels and high degradation based on extended servicing intervals'. A spokesperson for the brand also told us they were unable to trace DD's call to the Hyundai dealer that had told them the car had a full service history because DD had phoned using an ex-directory number.

Despite this, Hyundai has offered to waiver the cost of the new engine and parts but not the cost of labour to complete the replacement.