Well I know the recommendation is 5w30 to 5w40
but there's good offer on the shell 15w40 oil it cheaper by far and I saw friction test its very good oil but I'm concerned if it's very thick for my xj8 . I usually use 10w40 no problems
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Your headed does not say, where you are... - would be interesting in which climatic area you live...

ANyway - from google:
5w30 motor oil has a winter viscosity grade of five, meaning it's less viscous (less thick) at very low temperatures compared to, say, 10w30. It has a hot viscosity grade of 30, which means it is less viscous at high temperatures than an oil such as 5w50.

So I am driving 5W30 Castrol Edge, because it is a very good oil and it was on an extreme special. I guess 10W40 (or 5W40) would be better suited for Australia, but I bet, it does the job.

From memory the X308 recommendation is either 5W30 or 10W40. Thus, especially, if you do NOT live in any hot climate zone, 15W40 would be out of the question.

 

Hi mobile1,

I personally would not recommend 15W-40 oil in an X308, especially one with the AJ27 engine with variable valve timing. Using such a viscous oil could affect the proper operation of the timing chain tensioners, variable valve timing components and other engine components, especially at cold starts and during engine warm-up. The fluidity of the specified 5W- and 0W- grades was an important factor in the design of your engine.

You also should be aware that many 15W-40 oils are forumulated for diesel engines, with special additives to reduce ash/soot and other pollutants, additives that your engine does not need and which could damage your catalytic converters.

Another potential adverse effect of using a heavier-than-specified oil is reduced fuel economy due to increased resistance to movement of the engine's internal parts.

Depending on your climate, here are the oil viscosities Jaguar recommends in your engine depending on your climate:



Note that neither 10W-40 nor 15W-40 grades appear on the chart.

Cheers,

Don

 

The 5-30 would be my choice no matter how inexpensive that 15-40 might be.
We are talking about the "life blood" of the engine here.

 

Just my opinion here, but whats the actual savings you're talking about here? $10-15 maybe? Not worth it to me, just use the manufacturer recommended grades and not risk your car acting up.

 

We used Mobil 15W40 at the dealer for all Jaguars up to the AJV8 cars. (L6 and V12 engines)

5W30 for all V8 & V6 engines.

 

I was unable to find the recommended engine oil grades for AJ26 engines. The Jaguar Technical Guide updates for the AJ27 engine showed the following.

Technical Guide Update 1999 (NA AJ27 introduced):


Technical Guide Update 2000 (SC also AJ27):


It appears that the table shown in the MY2000 Update, which does not include 15W-40, is for the NAS markets only. Why only for the NAS markets, possibly due to a requirement to improve fuel economy.

As the MY2000 recommendation is relevant to the NAS markets only, I would conclude that for all other markets the oil viscosities table shown in the MY1999 Update applies, i.e. that 15W-40 is still recommended. Of course, only where (or when) the temperatures do not fall below freezing. 15W-40 should also be technically good for the NAS markets as it seems that it was excluded due to regulations and not because it is bad for the engine.

 

Could it be that the change in oil specification coincided with the introduction of Continuously Variable Valve Timing, or that there were problems with the CVVT system when running heavier oil, especially at cold starts?

In the U.S., there are not many parts of the country where the temperature never falls below freezing, which, according to the 1999 ROW chart M provided, would be another reason not to use 15W-40.

 

Reading again the comment under "Oil Specification" in the MY2000 update, although not totally clearly written, it could also be understood that only the first sentence (referring to spec API & ILSAC) is a requirement specific to NAS markets and that the second sentence (on the oil grades) applies to all markets?

 

will give it a try in summerthe previous owner used 20w50 but I believe it's too heavy and not necessary so it's okay to use 15w40
For now I used 5w40 Mercedes OEM oil