BogMonster Posted August 11, 2008 Share Posted August 11, 2008 Looking for informed views on the following please. Old V8 engines (3.5, 3.9 up to the end of Discovery 1 production in 1998) have a mineral oil specified e.g. 15w40 (there's a range of viscosities depending on the temperature but for the range -10 to +50 its a 15w40 or 15w50) SG or SH according to RAVE Later 4.0 Thor engines (such as in my 2002 Discovery II) specify a 5w30 synthetic ACEA A1 or API SJ Why? There has been some discussion on "which oil is best for a V8" in the past on here but I don't think I have ever seen an explanation as to why what is basically the same engine block etc, has two fairly different sorts of oil specified by the manufacturer. - Is it just because on the later vehicles the quoted service interval is 12000 miles (yes I know that is too long for a V8) hence needing a synthetic to "stay in grade" longer? - Is the oil pump/relief valve/something else different to NEED the oil to be thinner? I know the oil pump changed somewhere in the 3.9s but not sure what is fitted to the Thor engine - is it the same as a late 3.9?? - Is there another reason or physical change in the engine - if so what is it? The reason I am asking is because of the cost of synthetic oil here is now near 5x the cost of mineral oil and I can't immediately see a reason why I shouldn't run a Thor V8 on a 15w40 mineral oil (good quality Castrol Tection T 15w40), same as my old 3.9, given that it has 6000 mile changes (sometimes less) but then why would the spec be changed if there was not a reason? The vehicle is not doing anything unusual, will be operating in a temperature range -5 to +20 C (usually somewhere in the middle of that) nor sustained high speed, towing or off road use. Is there a cast-iron reason for NOT using a good 15w40 mineral oil in a Thor age V8? I have re-read this http://forums.lr4x4.com/index.php?showtopic=27742&st=0 but it didn't answer the above question just made my head hurt I don't wish waste the best part of £100 on oil for each change if I can do it for much less, and I can't see why the oil that my 3.9 was happy running on, shouldn't do the 4.0 as well? Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted August 11, 2008 Share Posted August 11, 2008 TheThor engines have a better oil pump and were manufactured to tighter tolerances………. Also I guess the 5- 30 oil will have a little less drag and produce marginally better MPG figures - something which needed to look good in the brochures at the time. However, I see no reason not to use a good quality 15 – 40………………….. My 04 Jeep Cherokee is much the same …………. For the 2.8 VM common rail diesel, DC Jeep recommend in the USA to use 0 – 30 fully synthetic, however, the next paragraph refers to ‘export’ cars and then recommends a 10-40 semi synthetic! I have always used the 10 -40 and it is now coming up to 100K (much of it trouble free – touch wood). Quote Link to comment Share on other sites More sharing options...
BogMonster Posted August 11, 2008 Author Share Posted August 11, 2008 Thanks Ian Would the tighter tolerances mean problems with thicker oil or is it not enough to make any difference? My engine has 37k miles on now anyway so everything has loosened up a bit anyway I expect. Not bothered about MPG etc as it is bank breakingly expensive anyway so not gonna make much difference The low compression engine is specified in RAVE as using 10w40 which is odd as I would have thought high and low compression engines would be much the same Quote Link to comment Share on other sites More sharing options...
missingsid Posted August 12, 2008 Share Posted August 12, 2008 I have no information to back this up so it is just "colour" I guess. My mate (as allaways) refused to pay the cost of Synthetic oil when he took his Lexus V8 for a service. He asked the garagr to explain why it had to be Synthetic and not Mineral oil. The garage could not bring any argument and agreed to use Mineral oil and maintain the Warranty, and to lower the service charge accordingly! If it comes down to tight tollerances then I would suspect that a Lexus V8 is a bit closer made than a RR V8? Marc. Quote Link to comment Share on other sites More sharing options...
JimAttrill Posted August 12, 2008 Share Posted August 12, 2008 Thanks for asking this question, Steve. We have been wondering the same while using 15w40 SJ Shell Helix in all V8's whether 3.5 or the 3.9 or 4.0 litre versions. We have used Redline 10w40 in one engine with a very rich owner, it is a very good Class 5 oil and I don't think we will change it for a while. We will get it tested first, worth it at that price. I think the thing about tighter tolerances is not that you should use thinner oil, but that you can use thinner oil in order to save fuel. With a modern engine that has been designed from square one to use thin oils like some mercs and beemers (and possibly the Lexus as above) then I reckon you should use the thinner oils. But again, it's your engine and your money. I rather disbelieve that the tolerances were changed much on the Rover engine from the start to the end of production. Given the ability of LR to not change things they should, I cannot think that they would spend a lot of money changing something you can't even see. Quote Link to comment Share on other sites More sharing options...
BogMonster Posted August 12, 2008 Author Share Posted August 12, 2008 Given the ability of LR to not change things they should, I cannot think that they would spend a lot of money changing something you can't even see. Harsh but probably fair Quote Link to comment Share on other sites More sharing options...
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