At the moment I am using Magnetec 10/40 in my 1989 XJS V12 and getting an oil pressure of 40-50psi.

This Car has done 58,000 Miles. Now due for another Oil Change.

If I were to use 5/40 instead of 10/40 would I get a lower oil pressure reading or would it not make any difference?

I've got a couple of unopened cans of 10/40 which I could use in my Merc, as from what I have been reading in some other posts 5/40 is the Oil of Choice for an XJS V12.

Someone please correct me if I have got this wrong.

 

OB
I always use the cheapest major brand fully synthetic I can find, 5W, 10W makes absolutely naff-all difference to the car. At least for the 120,000 miles on the engine to date.
Greg

 

Yes, the number rating on the oil is the viscosity. The lower the number the "thinner" the oil is. However we run oils that change viscosity rating with temperature. So an oil with a rating of Xw-Y would mean at colder temps it acts as if has a viscosity rating of X and as temperature increases it transitions into a viscosity of Y. The viscosity and temperature of the oil and the journal bearing gap size directly relate to your oil pressure. So with all of this in mind I wouldn't run anything lower than 10w-40. I run 10w-40 in the winter and 20w-50 in the summer. Without going into much journal bearing theory, if you choose too low a viscosity rating you risk damaging/wearing out your journal bearings, due to lower oil pressure. The lower the oil pressure the higher the risk damage will occur as the bearing are merely a film of oil supporting the rotating components. The only trade off in running a thicker oil is it takes a little longer to warm up in winter which is why I run 10w-40 in the winter. I remember seeing a chart jaguar produced that shows the recommended grade based on the average outside temperatures. I will have to search for it.

 

From the Jaguar service manual......

15ºF and higher : 10/50 15/40 15/50 20/40 20/50

-5ºF to 60ºF: 10/30 10/40

15ºF and colder: 5/20 5/30 5/40

Obviously there is some overlap, as you can see.

FWIW I also ran 20/50 in the summer and 10/40 in the winter, as mentioned above. In below freezing conditions I could tell the engine was laboring a bit to crank with 20/50

Cheers
DD

 

OB,
This may be the chart 86jag was speaking of.

 

Hi Greg

As I mentioned in another post, I found 2 Cans of Magnetec 10/40, so since I already have this, I may as well bang it in with a new filter.

 

I have already got a couple of Cans of Magnetec 10/40, which I found in the Shed, so I think that I may as well use that and top up with 20/50.

Thank you for replying that is all very useful to know.

 

Hi Doug

Many Thanks for replying, as I have 9 litres of Magnetec 10/40 I may as well use that and then top up with Magnetec 20/50.

BTW Did you put a photo up of your White XJS when filling up with gas at the Garage?

That was a great photo! which I thought was very Atmospheric and really captured the Spirit of the car.

I haven't been able to find it (as I don't know all the ins and outs of how these forums work) but it would be appreciated, if you would like to put it up again.

White does not suit every Car but that XJS just looks Awesome!

 

Hi Bill

That was very useful, so Thank You for putting that up.

 

Must've been someone else. I haven't owned an XJS in years....an unfortunate situation I'd like to remedy one of these days


Cheers
DD

 

5W40, 10W40 is fine for your car... lower the first number the better for cold weather starts. The second number is the viscosity at warm engine... I currently use Mobil 1 HM 10W40 but will be switch to 5W40 on my next OCI... May even try Mobil 1 0W40.

 

0 W 40? Is there such an oil?
RagJag.

 

I have been using Mobil 1 0w40 for quite some time now.

Fairly easy to find.

 

Lets hope you get one soon Doug

 

With the Changeable UK Weather, 10/40w seems to be middle of the road and as I've got a couple of Cans, I may as well run with that and see how it goes.

 

How does your V12 like the 0W40?


My 90 XJS seems to run very smooth on Mobil 1 HM 10W40 and so far has zero leaks. LOL. I have heard from many collector car sources that Mobil 1 0W40 is a fantastic oil.. I'd try it but its hard to switch from one that has performed well. I do have the itch to try something different though. Maybe at the end of the summer. LOL. Thanks.

 

I have the six.

The zero is only a factor at startup. Once the engine is warm, it is a 40 weight, just like yours.

I typically use Mobil 1 15w40 for the summer months and then 0w40 for winter.

 

Here in Wisconsin I store my XJS for the winter months. I do know of a few XJS owners in TX that use 5W30 in there cars but I'm sure I do not want to do that. I may give M1 0W40 a try in a few weeks here for the Summer... Thanks.

 

Also, my oil pressure has not dropped at all from going from a 50 weight down to 10W40... But, I only have 32K miles on my car.