According to the previous owner of my car he said that it was running synthetic, but did not specify a brand. There are not that many options out there other than Amsoil, Royal Purple, and other racing use oils that are 20W-50 synthetic.

 

I use Mobil 1 10w40 high mileage year round in Texas for my AJ16 1995 XJS.

 

Using 10W40 is not going to make that much of a difference compared to the 20W-50? Here in Vegas the weather starting to get hot. Will the type of oil used matter is such harsh weather?

 

I have used 0w40 and 15w50 in mine, both Mobil one full synthetic. From my observations on the psi I would recommend 0w40 for cold weather and 15/20w50 for warm weather

I've never used dino oil in mine but I'd expect the psi to be a bit higher obviously. However I prefer to use Synthetic since an oil change is fairly expensive on the 5.3 and I feel better with synthetic if I don't get it changed right at 3k miles.

I'd like to remove my cats to free up some power and be able to use a zinc additive.

EDIT: that being said if you have an oil leak you are probably better off with conventional until you fix it. Synthetic has a way of squeaking into tighter spaces, so it leaks more and carries a slightly different pressure.

 

Mobil 1 0w40 in winter
Mobil 1 15w50 in summer

I live in the Washington DC area.

 

Assuming you have a 4.0 6 cylinder 10/40 should be fine.

The V12s (and their owners) traditionally like the xx/50 weight oils.



By "type" do you mean viscosity, brand name, or conventional vs. synthetic?

As for viscosity the near universal recommendation is heavier weight in high heat situations.

As for brand name and conventional v. synthetic....well...seems like everyine has an opinion (often very adamant) and a favorite (often fiercely loyal). Me? I'm very liberal minded....or some might say a bit slutty. I'll go to bed with whatever brand is on sale that day :-)

Broadly speaking the synthetics are known to do well against high heat. Nothing wrong with that, obviously. Can't hurt, can only help...especially if you're a hard driver.

OTOH, long before synthetics became commonplace Jag owners and the residents of Las Vegas were getting along perfectly well with conventional oils :-)

Cheers
DD

 

May I ask why?

 

I found some 20W50 Synth

 

In Houston it gets to the 20's in winter can get up to 100 in the summer. The Mobil 1 full synthetic High Mileage 10w40 works well. I changed over from dino oil at 90k miles and it did make my cam cover and the o-rings on the motor oil cooler lines weep more, but after I replaced the cam cover and cooler line o rings, I have had no more leaks since then (2 yrs ago)

Personally , based on what I know about oils (which may be wrong) I would never use anything over 10w on any car made after 1970, including my V12 e type. If I had owned the cars from new , the XJS would be on REDLINE 0w40 year round and the E type on Amsoil Z rod 10w30. But because they weren't mine from new they are both on Mobil 1 high mileage.

 

In short this engine was designed at a time when oil had zddp and it no longer does due to catalytic converter restrictions.

Whether the design of the older cats matters less, if it was unknown that zddp was bad for cats, or if its just that manufactuers want cats to last 150k+ before being replaced, fact is that is what the engine was designed to run and I'd like to use it.

 

Understood- this is a concern with many older engines with flat tappet lifters. The latest oils still have ZDDP, but potentially not enough to avoid cam or lifter wear. The typical work around is to buy an off the shelf dual certified oil with the API certification of CJ-4, with Rotella from Shell being the most widely available.

Saves buying an oil with possibly insufficient ZDDP, then blending in an additive and hoping the end product is 'good enough'.