I put 10w40 in my 1993 XJ40. The owner´s manual didn´t specify any particular oil as it did with my S type.
A Jag tech later told me that he always uses 20w50 in these cars. I thought that might be a bit thick in cold start up so went with the 10W40 especially since the car´s maintenance history was unknown to me.

In the 1992 XJ40 I got a couple of days ago, the owner has been using 20W50 from the get go, so I will continue with that.

Is it ok for me to use the 10W40 in the first one,,,,at least for this oil change? It has exactly 100K miles on it. I live in a warm but not extremely hot climate.

 

One time I used 10W 40 Castrol Magnatec in my '88 3.6 but my Jaguar Specialist insisted on that such a visco would do nuttin but bring some harmful effect on my ride due to its thickness yet insufficient pressure
Unlike what you read above , we do use 10W60 Castrol , it was recommended all of my mechanics not only my Jaguar Specialist .

 

I have a 1993 XJ40 which I have had serviced since new by a Jaguar main dealer. They (in UK) have always put 10W40 in it. After ninety-odd thousand miles the engine is still factory fresh so 10W40 has not damaged it.

Do you have the original handbook for your 1993 car? There is a recommended viscosity / ambient temperature chart on page 289.

David

 

Thanks. David. Well I had a Jaguar tech who lives in a cold weather state tell me that they only use 20W50 in XJ40´s in his dealership and the owner of the 1992 XJ40 that I bought who always has used 20W50 both recommend that viscosity to me.
Generally I thought 20W50 would not be beneficial because it would take longer to lubricate the cylinder head in a cold start up.
However being new to Jaguars I took their advice and today I dumped the 10w40 and filter that I put in just a week ago and switched it to the 20w50. That´s a lot of oil down the drain (ok recycle bin). I hope it works long term. I don´t know the history of the 1993 so I figured I better play it safe. If it had the thicker oil in it all along switching to the 10w40 might not be good. If it´s always had the 20w50 I guess I have nothing to lose.
If anybody else would like to share their experience I would appreciate it.

 

I have always used 10W40 for both of my cars (Jaguar and Toyota) all year around. However, I use the oil for high millage cars. I periodically add Marvels Mystery Oil to top off as necessary. That reduces the weight of the oil slightly but help lubricate and cleans the engine continuously. Therefore, during the winter month, I don't have to worry about cold starts. The Marvels Mystery Oil keeps the top cylinders lubricated. I had always thought that 20W50 was a little too thick and should only be used if you have seals or rings that are going.

I've never heard or seen 10W60 oil.

 

After doing a little research from older threads I´ve found these from the jag techs here:


me personally have always used 20/50 castrol in all of my pre 97 jags
as well as this is the oil viscosity most if not alljag dealers use on pre 97 cars both 6 and 12 cyl (from IBJAGS tech certified)

and:


ibjags is correct, 20W50 is best for XJ40 in warm climates. Use 10W40 only if you live in a climate where you regularly see weather below 40 degrees F. The 20W50 turns to peanut butter below 30F. (from JAGTECHOHIO tech certified)

 

I put 10/40 in my 170k 4.0 XJ40 and once warmed up it had low oil pressure, on warm days the oil light came on on tickover, i added a good quality oil additive and now the problem has gone. I think i will be going for a thicker oil on the next change.