I believe my engine was overhauled in about late 70's to 80's. Has had very little engine time since then. It seems that would be about the time they went to unleaded fuel. Would it be adviseable to use a lead additive? Suggested brand?
59 XK150S

 

If it was overhauled properly it will have the hardened valve seats. Additives to some are needed but unless you are driving hard or racing all the time it is not necessary. I have driven the pre-70 Jags to 200K miles and never had a valve problem to no lead fuel. Bigger problem is pinging from too low octane. The pinging can really tear up the aluminum head.

 

It's very doubtful the valve seats will have been replaced; this is a big job, and in the 70s would have been very unusual.

As Jagfixer says, it is not usually necessary on these engines as the valve seats are normally hard enough for the kind of useage these cars get nowadays. Jaguars have been able to take unleaded since the mid-sixties,, although your cylinder head is earlier. I believe, though, all these engines had chilled cast-iron valve seats from the start. I may be wrong thogh.

However, if you're a bit nervous, try Castrol Valvemaster: -


There are two types, the "Plus" variety also has an octane booster. I use it all the time in my MG Midget engine. The bottle has its own measurement device. It just takes slightly longer to fill up at the filling station, that's all.

 

Hello,

Addtive is never needed on the XK engines.
All heads received hardened Valve seats from Day one!!
I use Euro 95 ( unleaded fuel ) for more that 15 years on my 3.8 S-type now.
Valve clearance is still OK, after all these years ( about 25.000 Km )

Regards,
Peter Jan

 

If your really keen on converting your unleaded to leaded as opposed to merely using an additive i can recommend this TetraBOOST: Product Information

Not cheap but it does what it says

 

Thanks to all for the input. Looks like it is unanimous.
Does anyone know where to purchase gas without ethanol? I think someone said you could buy it in the Seattle area. Would rather stay away from Avgas considering the cost.

 

Ethanol-free gas stations in the U.S. and Canada
Vector