Not looking to start an oil debate

It’s winter time now and if I was dealing with a V12 I think that 10W40 or 20W50 would likely be at the top of the list.
Does the 4.0 require a different viscosity to the V12?
I was looking at the Motul website and they have 10W40, 15W50, and they even have a 20W60. Any suggestions?
I’d like to think that a synthetic would be the way to go, but is it the right type of oil for the six cylinder?

Of course synthetic is the right type of oil, but so is the good ole dino stuff.

I would recommend looking in your manual and seeing what the recommended weights for oil are in your climate. Keep in mind that 0w oils weren’t around, so you’ll have to extrapolate where a 0w oil would fall.

The main difference between synthetic and dino is longevity. If you plan on changing every 3,000 miles, go with dino. If you want to take advantage of the extended life of the synthetic, I would go for synthetic.

The problem here is that synthetic has gotten to be so inexpensive, there are really no great reasons to avoid it.

I run 0w40 in my 4.0 liter all year round. I subscribe to the theory that the number to the left of the w can’t be too low. The right side of the w has to be a 40 or 50, or even 60, if you live in the right area! If they made a 0w50, inexpensively, I would buy that. To argue between a 0w and a 5w or a 10w is a waste of time…in my opinion.

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And in mine, too: ANY brand that’s on sale is just fine.

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I agree – but I live in Florida. It’s that side of the W that’s important to people who want to start their Jaguars when there’s several feet of snow outside.

As I understand it, the separation between the low number and the high number has an inverse impact on the longevity of the oil. All synthetics are very durable indeed, but in theory a 10W-50 will last longer than a 0W-50. Something to do with the chemistry involved.

I am under the impression that overhead cam motors, especially, can benefit from presence of zinc in the oil. There are just a few oils currently that claim zinc for their selling point. Zinc somehow reduces wear in the “sliding” action that occurs between the cam lobes and the tappets of the OHC motors. Is this a consideration for Jaguar owners? I currently do not have a running Jaguar but have been using Valvoine 20-50 Racing, for example, to address this concern. Thanks.


It’s not necessarily OHC, but rather flat tappets.

Some people swear by oil for diesel engines because it supposedly contains more zinc.

Uh, :thinking: that is very interesting. With Dino :sauropod: around 3,000 miles is where I normally change. Do you suppose :100: synthetic could last 6,000 miles?

Well, the V12 has flat tappets, no clue about the internals of the 4.0

My policy is to use full synthetic and change it at manufacturer’s recommended intervals, which is usually considerably longer than 3000 miles.

Check. Dino oil on sale. both my critters get 20/50. many prior critters did just fine on it. the clime is mild here.

Of course Kirby, you wrote the book, but can I respectfully disagree for two seconds here. My dear old Dad., my uncles and just about every other relatives I have from England say if it ain’t broken don’t mess with it. They all come from a long line of aircraft and old English car mechanics that say continue with the recommended manufacturers oil, (in my case Castrol 20/50 W dino ) and you will avoid a heap of problems. Mainly oil’s leaks. I’m going out on a limb here but a little bit of sludge to seal things up is not a bad thing. I run synthetic oil in all my modern engines , but stick with the good stuff in a 5.3L V-12 designed after WWII. Guess how many oil leaks I have? I can post a picture of my oil drip pan.

I must admit that, that perspective does have a way of bringing things back down to earth. I do wonder, though, if the oil leaks associated with the synthetics are more common to older cars that are only occasionally driven as opposed to daily drivers? On the other hand, I venture to say that most of us (not all) who drive and maintain these old Jags have other modern day cars that are driven as dailies, and more so in inclement weather conditions, thereby creating longer sit times. I presume that after Ford took over the reigns the facelift models going forward were less prone to oil leaks.

Typically in older design engines without roller cam interfaces, like ours, you want an oil with a higher content of ZDDP, a zinc/phosphorous compound. Higher content of ZDDP is typically found in oils designed for higher mileage engines. One of the higher ZDDP content oils happens to be Mobil 1 15w-50, which is what I run. I’ve seen some data that separate ZDDP supplements for lower ZDDP content oil are not as good as oil whose additive package is optimized for higher ZDDP by the manufacturer.

The oil leak idea of synthetics is a myth. Think about it. The only two rotary seals on the V12 engine exposed to the outside are the front and rear crank seals. The front seal is a modern type of seal used in new designs. The rear rope seal in older V12s could care less what type of oil it sees, as long as it is clean. Everything else is a gasket, o-ring or rubber plug, all of which should be replaced in a 30 year old engine. The older V12s have the junk paper gaskets that leak whatever oil you use. Update to the newer “gortex” style gaskets in the Jaguar service bulletin, and use the recommended, torque retaining fasteners with them, and leaks disappear. Use Viton o-rings where you can. Also, seal the threads of the fasteners going into the sandwich plate as in the other service bulletin. Clean your breather gauze under the pig snout regularly to prevent crankcase pressure buildup, which is another primary cause of leaks; if you can’t see light thru it, it’s not clean enough. Run and exercise your engine regularly; inactive engines also cause leaks. Run a high quality oil, synthetic or dino, of the proper weight and change it regularly. I happen to be partial to Wix or Baldwin filters, but use a quality oil filter.


I’m surprised nobody has mentioned this, but synthetic oil has a more consistent temperature and viscosity. All molecules are identical size. I assume this makes a difference, especially for the V12 which can have very hot temperatures.

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Yep, tons of information out there about the myth of synthetics causing leaks. First iteration may have, but been remedied for a very long time.

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I use Valvoline Racing, but there are also Joe Gibbs (aka Driven) and Brad Penn brands that have ZDDP. I hear Toyota dumped a lot of money in R&D for the former.


I use the Joe Gibbs Driven exclusively in my Porsche 996 and have also used the Brad Penn in it as well. AFAIK the later facelift models don’t have flat tappets like the V12 so the ZDDP isn’t needed. Although not particularly easy to get (at least not in my neck of the woods) I went ahead and ordered the Motul 8100 X-Power 10W60, it’s 100% synthetic and is meets the A3/B4 ACEA standard so we’ll see how it goes but I don’t anticipate any ill effects from the Motul brand as I have been extremely happy over the years with great performance from their oils that I use in my motorcycles.

I just dunno, I feel the original poster didn’t want to have an oil debate, but I’ve become a firm believer in if it ain’t broken don’t fix it. We have a lot of JL’s here say well I changed my oil to synthetic and the next posts you see are , well I’m leaking oil at the oil pressure switch and now the oil feed banjo bolts.
Here it is if you use the specified oil from the manufacturer and stick to the oil change regime you wont have any issues . If I decided to drive my car as a year round winter car I would definitely consider a change. But for me it’s a well maintained hobby car.