XJS & XJ from KWE Cars
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All you need to know about: Classic car engine oils

The temperature conundrum

Engine oil viscosity is a measure of how runny it is, thus indicating its ability to coat and protect metal bearing surfaces from rubbing together metal-to-metal. Oil viscosity is quantified by a number, usually from 0 (very thin) to 90 (very thick). But this viscosity is inversely proportional to temperature, so hot oil is runnier and less able to protect big gaps as found in older engine designs, and cold oil is heavy and sluggish, draining some engine power and again reducing protection. So a fixed-grade oil has to be thick enough to protect the engine at maximum temperature but this means it will be very thick at cold temperatures, making the engine very hard to start. Cold climate drivers sometimes have to resort to heating the engine with a paraffin heater before they can be started!

XJ classic car oil

Many years ago, engine oil was blended to be ‘visco-static’, which meant it behaved as a thick oil when hot and a thin oil when cold. This allowed easier starting in cold weather, and good protection when hot.

The terminology will be familiar: a ’10W-40’ oil behaves as a thin 10-grade oil in winter weather and a thicker 40-grade oil when hot.

Classic car engine oils

The Jaguar V12 engine and all 6 cylinder engines before the AJ6 engine of 1980’s vintage needed quite a thick oil – usually 20W-50 – partly because the engineering tolerances were not so close as they are today with modern manufacturing methods, and one needed a good thick oil to fill up those tolerances. As engine manufacture got better, one could use thinner and thinner oils that gave as good protection but much reduced drag. Rather like stirring a cake mix, it’s hard work churning up thick oil inside the engine and loses a fair amount of power.

Which oil should I use in my classic car?

The AJ6 and 16 engines are happy with 10-40 in UK climate, but a worn engine will benefit from 20-50. The late 6 litre V12 is better made than the earlier 5.3 so can use 10-40 oil, but the reduction in friction is tiny compared with the massive friction of 12 pistons so there’s no real advantage to be gained. Castrol offers a high quality 10-60 mineral oil and this is fine for the V12. The Jaguar manual shows 5W-50 oil as being satisfactory for the AJ16.

There is another important factor to consider in oils (amongst many). Oils’ second-order properties are graded, usually by the American Petroleum Institute’s API nomenclature. Without getting into the chemistry, the later in the alphabet the coding is, the better quality the oil. Early oils might be API SC and the XJS and XJ cars require a quality of API SG or better. 20-50 SG is not easy to find these days, although Halfords sell their 20-50 ‘Classic Oil’ at the time of writing, but this is only API SE – not really good enough for ‘our’ engines.

There is no point in putting very thin, exotic synthetic oils such as Mobil 0-10 in the XJ engines. The engine will be noisier and leak more.

There is no great harm in mixing fresh oil, so while all V12 engines will leave KWE with 20-50 in them topping up with 10-40, 10-50 or 10-60 is acceptable if 20-50 can’t be found.

KWE has its own 20-50 specially prepared.

11:11 am KWE Cars

19 Comments

  1. Alex-
    December 8, 2015 at 9:45 am

    What oil do you recomended for xjr 4.0 97′ x308? Thanks

  2. Chris Knowles-
    December 8, 2015 at 11:07 am

    We recommend a 10-40 semi synthetic, API SJ. If the engine is heavily worn you might go to a 20-50 but this is difficult to find in API-SJ form. The ulitimate is Castrol’s Edge – a 10-60 – but it is numbingly expensive!

  3. Donna-
    April 6, 2016 at 11:55 am

    Hi how much and which oil for a V12 jag

  4. Chris Knowles-
    April 6, 2016 at 1:54 pm

    10 litres, 20W50 API SG

  5. John-
    August 7, 2016 at 2:39 pm

    Hi, would Fuchs Titan Race Pro R 15W-50 be suitable for a 1973 E-Type V12?

  6. Chris Knowles-
    August 8, 2016 at 2:16 pm

    Yes, it would be fine, but very expensive at over £50 for 5 litres. The Jaguar V12 doesn’t need this level of technology and you will gain no noticeable benefits. But a 10-50 is good; you might also consider Castrol Edge 10-60 which is even better in terms of static viscosity and a touch cheaper at £42 for 5 litres. In general it is better to replace the oil more frequently and use the best filters, rather than put in mega-expensive oils…

  7. Charlotte-
    September 12, 2016 at 9:08 am

    Hello,

    Which oil do you suggest using for a 1956 jaguar xk140 e-type head?

    Thank you so much in advance!
    Charlotte

  8. Chris Knowles-
    September 12, 2016 at 9:17 am

    Hi Charlotte, I’d recommend a mineral (i.e. non-synthetic) 20W50 oil such Castrol 20W50 – http://www.castrol.com/en_us/united-states/motor-oil/conventional-motor-oil/gtx-motor-oil.html

  9. Charlotte-
    September 12, 2016 at 9:23 am

    Hi Chris,

    Thanks so much for your quick response. Can we top up with your suggestion on top of penfolds?

    Thank you!

  10. Chris Knowles-
    September 12, 2016 at 9:40 am

    No problem. And yes, you can top up on top of Penfolds (or any oil).

  11. Ted Warren-
    October 28, 2016 at 11:41 am

    Hello,
    I have a 65 Jaguar E Type OTS. Is the Castrol Classic 20W50 a good choice for oil for this car? And if so, where can I buy the products in USA?
    Thanks,
    Ted

  12. Chris Knowles-
    November 7, 2016 at 4:49 pm

    Yes the Castrol Classic 20-50 is perfect for your E type. Seems to be available from Castrol US here: http://www.castrol.com/en_us/united-states/motor-oil/conventional-motor-oil/gtx-motor-oil.html

  13. Nicholas James-
    November 23, 2016 at 8:29 pm

    Hello, I have a 1989 5.3 v12 XJS and I’m trying to find a reputable 20w50 oil. Does it matter if the oil is mineral, semi synthetic or fully synthetic – would the Silkolene 20w50 Classic/Historic/Vintage Silkolube work okay? Alternatively, how do I get hold of your 20w50 oil?

    Thanks

  14. Chris Knowles-
    November 24, 2016 at 12:01 pm

    It doesn’t matter what type of oil you use – the engine was designed for mineral oil but semi or full synthetic won’t harm it but it’s not worth the extra expense. As far as manufacturer is concerned it doesn’t really matter provided the oil meets API SG specification or better. (SG is good, SH is better, SJ is current and very good; SE or SF is not good enough – see http://www.oilspecifications.org/api_eolcs.php). We don’t send out oil any more, but if you were passing by we can fill a can for you (bring your own can)!

  15. Nicholas James-
    November 24, 2016 at 3:04 pm

    Chris,

    Many thanks for your response, I’ll see if I can make a trip over to you guys at some point.

  16. Jeff-
    January 2, 2017 at 4:35 pm

    I have a 1987 xj Vanden plas. 5.3l v12. It has 120,000 km on the dial. What is the best oil and filters I should be using for best performance?

    Thanks

  17. Chris Knowles-
    January 4, 2017 at 11:45 am

    For best protection of the engine use a high quality 20W-50 oil – Castrol, Havoline, Millers et al. For best performance one can reduce some of the starting and running stiffness by using a thinner oil such as 10-50. The ultimate is Castrol Edge 10-60 but it is very expensive.

  18. Ian Kingdon-
    January 8, 2017 at 4:05 pm

    Not sure if I have correct site. I have a xj v8(X308) 1998 4.0L engine mileage 153500 Pls recomend oil grade Thanks

  19. Chris Knowles-
    January 10, 2017 at 5:33 pm

    You will find that the handbook advises 15W40. Semi synthetic is fine. If you are likely to meet temperatures much below -10degC for long periods then go to 5W40

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