I just now realized that I have been running 5W-20 engine oil since June (about 1500 miles) instead of 5W-30 in PR climate.

Is the slight less viscous oil weight likely to be a problem? Should I do an oil change to 5W-30 now or can I wait it out until the next scheduled oil change?

 

We suspect the later 4.2L engines called for the 5w20 due to fuel mileage as did other makes or Brands. Difficult to imagine Jaguar changing the machining tolerances on a engine that is Bullet Proof as the 4.2L you could just wait til next change if not maxing the engine or abusing it . My thoughts :-)

 

Ok, I didn’t know the later 4.2 engines used the 5W20. That is reassuring. I haven’t noticed any difference in how the engine behaves.

 

In the PR climate I’d think you’d be using 0-40 or 5w-40 .

I have used those oils in southern Texas which is similar to PR in air temperatures, and in Oklahoma too, with the 0w-40 getting winter duty.

after a few heat cycles the oil shears down a grade to essentially a 0w-30 wt

the vehicle care manual gives a sliding scale of viscosities to use depending on your high and low temperatures.

A well priced high quality oil is the Mobil 1 0w-40. It should be readily available to you at discount stores.

Z

 

Interesting ..now the weather has cooled in the UK I note the piston slap is much reduced in volume I assume due to the oil being thicker .I am using 5W30 but contemplating using 10W40 in the summer . Any thoughts 4l non supercharged.

 

For your hot and humid summers, I would stick to the maximum viscosity listed on the manual: a 5w-40, in a quality synthetic of course.


Z

 

PS:

according to the XK oil recommendation chart included in car care manual the “sweet spot” for using a 0w-40 viscosity oil is 50-85 degrees F or 10 to 30 degrees C.

does that include most of the PR temperature swing ?

If you are expecting a low temp temperature higher than 50-60 F / 10-15 C, and highs above 85 F / 30 C, then the 5w-40 is your recommended viscosity.

Z

 

PR temperature fluctuates between 65°F as the coldest in the winter in the mountainous towns, to 112°F in the summer. Most of the year is between 82°F and 92°F.

I think you’re right about the 5W-40

Today’s high was 89°F.

 

unless you are driving a lot in the coldest part of the winters, I think the indication would be 0w-40 year round. That would give you the (charts) suggested maximum protection from 5 C to 30 C.

Z

PS there appears to be no distinction between XK8 and XKR in the manual as pertaining to recommended oil viscosity.

 

This is the recommendation for my 2003 4.2 XKR. Unsure if this differs to the XK8.

 

the 3.9L 30/35 used 5w20

not a big deal move on with your life

 

Oils all thin down significantly at operating temperature to about the same viscosity. Yes, the 40 will be slightly "thicker" when it thins as it started a little higher, but not enough to factor into more prevention from destruction. In the days of non-synthetic oils, there was the issue of the lower starting viscosity beginning to shear which was a problem. There was a top temperature where the oil could not perform, essentially a cut-off. The 30 in conventional was rather close to the maximum temp expected, so if there was some overheating or hot spots, there could have been an issue. The synthetic versions, the cut-off is so high that the engine would be destroyed by other issues related to temperature too high. Why do i bring this up?

The higher number 20, 30, 40, whatever is part of the cold start pump up situation. When an engine is cold, its clearances are wider. The thicker oil when it is also cool fills these spaces, gets pressure up quickly to isolate the movement of these temporarily looser moving parts. As the engine heats up the clearances get tighter, requiring the oil to thin down in concert. Note that this was what happened even in the days of straight weight oils. The lower number with the "w" is merely a performance test. Some oils actually pass this test for lower numbers but do not get the cert because of all sorts of rules regarding additives which must be present. Translation: many 10w and 5w are as good as 0w in cold performance even though labeled otherwise. I think that the Jaguar chart is merely making it easier for someone who lives in a hot climate to consider 5w-40 as 0w-40 might not be sold there for obvious reasons. Note that there was an old argument that the broader the range, the less likely the oil would hold up over time in various ways. True for some conventional and a good idea to consider with them, however not an issue now ... except.

Enter the 20, especially the 5w-20. This oil can be created and certified as blended product or conventional. The problem is that a truly good 20 cannot be created with any conventional contribution to the product. This is why the OEMs went to 0w-20 and made it backwards compatible with their 5w-20 specified cars. It is not possible to certify a 0w-20 unless it is full synthetic. In essence this creates a better user experience as the 0w-20 will protect the vehicle much better than the marginal products in the 5w-20 range. Thus, for the OP, simply make sure that the 5w-20 used was full synthetic. If not, dump it.

A while back someone here asked me why Aston Martin using the same basic engine specified 0w-60 and our units were held around 5w-30 and 0w-40. The reason is simple. Very efficient and smooth engines are tight engines. Very powerful engines are loose engines. If measured at cold spec, the AM version will have higher clearances and require the thicker product at pump up, and a slightly overall higher operating temperature viscosity.

The 20 viscosity has represented for automotive engineers a kind of holy grail in that it is the perfect operating viscosity for most uses as tight clearances have many wear benefits and other operational benefits, efficiency being one of them. Engines were designed for the 30 viscosity because making a good 20 for temperate and hotter climates was not possible before synthetics. For my old 67 Firebird the owner's manual listed the 5w-20 of the time for extreme cold climate conditions, yet cautioned not to drive at sustained highway speeds while using it. The conventional 20 maximum operational temperature is below the standard operating range of most modern engines of the past 40 years. This is why synthetic blends were used to make usable but marginal versions when it was brought into greater general use in the early 2000s. The manufacturers in many cases required their own oils to avoid failures by having control over the product. 0w-20 took a while to become common and available.

The key to lubrication involves pressure as only part of the equation. Flow is much more important, and excessive pressure is merely a bunch of wastes and potential damage. The faster the oil flows through the races, the better it separates parts.

Now we get into boundary lubrication which can occur in any engine, oil and viscosity. The oil gets so thin that the film breaks. The save from this are solids and other compounds added to the oil to essentially dry lubricate in these off chance or designed-in situations. This is why a while back i impressed upon people to use the Euro-spec oils with the highest amounts of these solids as long as they met the other API and other vehicle required standards.

So, why do i prefer the 40 in my sample of this car. It actually has as much to do with the brands of oil which i use as much as anything else. Most synthetic 30s are on the thin side of the range for a 30. Remember that the peak operating temp for this oil is still quite high and above anything which would be encountered. It is merely hedging a little to the thicker with a 40 that is also on the thin side based upon what i saw with oil pressure readings.

Lastly, why did the OEMs shift to 20 viscosity using the same hardware and specs and even back rate older engines. For the first part of this question, one must look at the USA EPA fuel economy and emissions testing. It is done from a cold start. They are splitting hairs here looking for very small increases in test numbers. The second part of the question is to make it easier for dealers to have bulk supplies. BTW, dealer bulk oil is not often the top of the line product.

I would never go below 30 in these cars.

Some very inexpensive full synthetic Euro spec oils (Full SAPS) are excellent performers. M1, Cas Edge, etc.

 

Very educational and interesting post WhiteHat. The oil in the car is Pennzoil Platinum Full Synthetic 5W-20. It is made from Natural Gas instead of crude oil. I have had a good experience with this oil in its 5W-30 specification on the XKR and as a 0W-20 in the Jeep I had.

This is the spec sheet for that oil:

 

That is a great oil, hard to do much better. Yes, i get the Natural Gas aspect, however the key is what they do to make it, not necessarily the base. The NG is just a way of not dealing with impurities which are a major factor in very high performance applications or touchy situations such as with pre-ignition. It is basically too good for our application.

My preference is for an oil which meets the A3/B4 spec for SAPS such as M1, Edge and Amsoil Euro, however Pennzoil adds other things which more than makes up for it. I need higher detergent and base number for my usage, perhaps when that changes will go to something else.

Stick with that brand, and you cannot go wrong. Next time just get the usual viscosity.

 

Yes, I know it’s good oil and it isn’t as expensive as the Liqui Moly I was using a couple years ago.