Engine Size

[jeff1954]

Hi This has probably been discussed many times, but what is the difference between the 4.2 and the 5.0Ltr normally aspirated engine as regards to fuel consumption/tax/insurance etc as I am thinking of buying one.

Jeff

[mike020150]

At one time I ran a 4.2 litre X100 convertible which was replaced by a 5 litre X150 convertible. My experience of the points listed goes like this. MPG At lower speeds, the 5 litre car had the advantage of slightly better fuel consumption but for faster journeys (probably faster than those in the 4.2 litre car), the 4.2 litre just edged it. Overall, there was very little in it either way but the 5 litre is a much faster car.

Tax Assuming you are looking at X150 (aluminium) cars, unless you find a 4.2 litre registered before March 23rd 2006 (if my memory is correct about the exact March date), both versions suffer the higher (approx. £500 pa rate). Don't set out with the immoveable aim to find a lower tax car. Buy the car in the best possible condition for your budget. Repairs to a bad car will soon eat up any tax savings.

Insurance Insurance is so variable between companies that the only thing you can rely on with reasonable certainty is that a more expensive car to buy is likely to cost more to insure than a cheaper car. Since 5 litre cars are younger and therefore more expensive, they are likely to generate higher premiums although not excessively so. Your claims record and location will have bigger effects on the premium.

Maintenance There are no significant cost differences between 4.2 litre and 5 litre X150 cars. However, to date, X150 cars have proved to be significantly more reliable than their X100 predecessors. Mike.

[jeff1954]

Thanks Mike for your reply. It is the X150 that I am looking at, 2005 to 2008. I have been searching for an late X100 but tales of rust and to many previous owners has put me off.

Jeff

[mike020150]

A 4.2 litre X150 is a very well-sorted car. With slightly lower gearing and less weight than an X100, it provides brisker performance with few common service weaknesses. A 5 litre naturally aspirated version (available from 2009 onwards) has very similar running costs as a 4.2 litre naturally aspirated X150 model but is practically as quick as the previous X100 XKR and it has upgraded quality interior trim. As long as you make the usual condition checks that you'd make on any 2nd hand vehicle, choosing the model becomes more a question of budget than anything else. Once purchased, even the X150 XKRs are not that much more expensive to run than the naturally aspirated versions. Mike.

[jeff1954]

Thank You Mike. All information gratefully received.

Jeff

[jeff1954]

Hi I've found an lovely 2005 X100 just round the corner from where I live (4 miles) but it's an R I have read that the R is quite noisy when you put your foot down because of the supercharger, is that the case. Also would the insurance be higher and the fuel consumption.
I have also read that maintenance is harder ie valley pipes etc. Any thoughts.

Jeff

[mike020150]

Well done on finding a local car to view. To answer your queries, a supercharged X100 does have a very distinctive noise when the throttle is wide open and the supercharger is working hard. Some people relish the type of noise. Others less so. It's simply a matter of taste. However, bear in mind keeping the throttle wide open is not something you can do on public roads for more than very few seconds at a time, otherwise your speed will be dangerously beyond any UK speed limits! In practice, it's probably unlikely noise differences between supercharged and non supercharged models will be your deciding factor whether or not to buy. Insurance costs can be higher for an R, although many classic policies and some others tend to lump both models together into the same high category. Typically, expect a 1 to 2 mpg fuel consumption penalty with an R compared with a naturally aspirated XK8. Again, for a low annual mileage car, the cost difference is unlikely to be especially significant. You can spend far more money rectifying a car with rust in it so ensure you check it carefully before purchase. Valley pipes are not regular service items and may last up to a decade without attention. Similarly, the supercharger itself only requires an oil change after a high mileage. Thus, maintenance costs are very similar for the two models. Mike.

[jeff1954]

Thanks once again Mike for the info.

Jeff