Full ester synthetic in early Jag XK engine

[RogerK]

I'm deciding on a long-term oil to use in my 1955 Jaguar XK140 engine, now that it's done 1500 miles since rebuild on Castrol 20W 50 classic oil. Main bearings are at around 0.001-0.0015" clearance, big ends at 0.0015-0.002".
I have an old Mustang which has always run on Fuchs Titan Pro R 15W 50 full ester synthetic, and even after 22 years and 60k miles the insides look like brand new when I drop the sump. I'd like to use this in the Jag, mostly because of the far better cold start protection (the car is likely to sit for 5-6 weeks between start-ups) and the better protection if the engine gets hot in traffic.
The likely problem could be leaks - the old Jaguars used a scroll 'seal' for the crank rear main, and I'm concerned that a synthetic oil will leak more from this point than the old mineral oil. Also, I guess the oil pressure will be a bit lower, but if the protection's better that's not much of an issue.
Any ideas on this?

 

[wings&wheels]

I have used Mobil1 15w-50, their motorcycle 10w-40 or 20w-50 and Delvac1 on my old fleet for going on 30+ years with no issue. Maybe a bit more leakage on the TR, but I will gladly trade that for the benefits of a quality synthetic. Have at it! Love the old XK's.

 

[Brian123]

I'm deciding on a long-term oil to use in my 1955 Jaguar XK140 engine, now that it's done 1500 miles since rebuild on Castrol 20W 50 classic oil. Main bearings are at around 0.001-0.0015" clearance, big ends at 0.0015-0.002".
I have an old Mustang which has always run on Fuchs Titan Pro R 15W 50 full ester synthetic, and even after 22 years and 60k miles the insides look like brand new when I drop the sump. I'd like to use this in the Jag, mostly because of the far better cold start protection (the car is likely to sit for 5-6 weeks between start-ups) and the better protection if the engine gets hot in traffic.
The likely problem could be leaks - the old Jaguars used a scroll 'seal' for the crank rear main, and I'm concerned that a synthetic oil will leak more from this point than the old mineral oil. Also, I guess the oil pressure will be a bit lower, but if the protection's better that's not much of an issue.
Any ideas on this?

Do you have Pics of both Cars? What year is your Mustang?

 

[RogerK]

It's a '68 fastback GT, which we've taken all over Europe.

...and the Jag's just out of restoration.

 

[addyguy]

That Jag is beautiful! Well done!

 

[Triple_Se7en]

That was always my-most favorite looking Mustang. A most similar look is Steve (King of Cool) McQueen's Bullitt