Just interested in the opinions of the brain trust on how often you use the ZDDP additive to an oil change. I’ve been using Mobil 15-50 in all of my v12’s both carbed and with EFI.
ortho3,
I recommend that you search the Jag-Lovers archives for “ZDDP” where you will find the hundreds of posts already written there with opinions every where from “a waste of money” to “the greatest thing since sliced bread, I wouldn’t leave home without it” and sometimes “WTH is ZDDP?”. 
Paul
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Mobil 1 15 50 ALREADY HAS the appropiate level of zddp, for flat tappet cam engines. The correc level is 1000 to 1400ppm. Do NOT add more. Other oils made for flat tappet cam engines…are available…from Castrol Classic, Valvoliine VR1, Joe Gibbs and others. Note that other viscosities DO NOT have the zddp level. So for Mobil 1, it is the 15-50, but NOT most of the others. As for oils not formulated with the 1000-1400ppm…the difficulty of adding a ZDDP additive is getting the ppm correct. Quite difficult if even possible. So just get the oil that is formulated alreade. OK…the debate about if needed…well maybe it is…the XK engine IS a flat tappet cam…but it can be argued that the valve spring pressure of tappet to cam is much less than V8 muscle cars…so that the zddp protective wear film is not needed…again…well maybe not…but there is NO harm, ZERO harm…in using a zddp oil, so why wouldn’t ya. I do not accept the arguments it is snake oil or marketing. There is plenty of evidence zddp is effective. Also…think of new cam install…one must ALWAYS use new cam lube on the cam or risk instant damage. WHY because it is zddp and puts in a protective film. Carbs, fuel etc are irrelevant. Zddp provides a thin molecular film in the pores of the cam/tappet metal. It of course is in contacrt with other metals in the engine wherever oil goals…the zddp film may be beneficial for any high metal to metal contact.
Nick
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To amplify what has already been posted you should beware of an excessive amount of ZDDP in the oil. It makes the oil acidic and promotes corrosion wear. Mobil1 15W-50 has all the ZDDP your engine needs. This is a case in which "More is Certainly Not Better
Google “is too much ZDDP harmful”, and you’ll find plenty of information like on this site:
https://aaoil.co.uk/123579-2/#:~:text=If%20you%20have%20too%20much,because%20of%20too%20much%20ZDDP.
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Correct John W…the correct range is 1,000 to 1400ppm…Valvoline VR is at the high range…but ok. That is why mixing an additive to oil is problematical. A good mathematician with graduated beakers could do it…oh…wait…they did…the oil companies that make it that way. If one was to err…on an XK engine, err low. On a 60s 70s hi perf muscle car do not err.
Nick
Thanks guys. I knew there was a reason I still had that small unopened bottle from years ago.
Soooo – since I am restoring my V12 and the engine has been near-totally revamped (original cams, BUT new pistons, cylinder liners, valve train pieces to include tappets , etc) is Mobil1 15W-50 the oil of choice for that soooo-scary initial start up?
When I reinstalled my rebuilt 4.2, I did the first 1,000 miles with Castrol 20W-50 conventional oil, mainly because I had a quantity of it on the shelf. My intent, and what I did, was to use Mobil 1 15W-50 after break-in. I probably could have just used the synthetic from zero miles with no problem. Modern car manufacturers that recommend synthetic oil, ut it in at the factory with no break-in issues.
I wonder what the well respected engine rebuilders, some of whom are on J-L, would advise?
Craig, frankly, any good quality oil that you put in it will be just fine!
You have original cams and tappets, which have already been worn in, and the rest of it simply is not a big deal. You follow the break-in recommendations that I will suggest, and the cheapest Walmart brand of oil will work fine.
To bed in the rings and bores over the first few hundred miles after a rebuild, it’s better to avoid oils with a lot of friction modifiers. Go for a basic grade mineral oil and after the first few hours of driving, give the engine a good to thrashing.
as Paul said…rebuild your prized Jaguar engine, spend a lot of money, pray it all is perfect and will run like a dream…and then save $12 by putting in the cheapest oil you can fine…makes sense to me…(I know …if it meets the API specs…oil is oil…well maybe not…oils can have specs that exceed that…better shear resistance, better thermal breakdown resistance, less foaming, moly, zddp, all kinds of formulas…do you pay for brand advertising yes…should you care when considering the oil that lubes your engine…No ! Hoping your new assembly has new assembly lube pre placed. Use a new engine rebuild specification oil… FACTORY new engines are run in AT THE FACTORY. The oil you get on deliver is NOT that oil.
Nick
Nick
Every engine in every Toyota, Nissan, Ford, GM, VW, etc? Sorry, but I’m doubtful. This article would lead me to believe a few do, most don’t.
I do not understand your comment…I do understand the link text…tho it is from “How stuff works”…and not direct from manufacturers or engine builders. Altho some run in the engine longer…some shorter…All ENGINES ARE TEST RUN before install. I will BET that that engine oil is drained along with filter. If you are gonna warranty an engine for a 100,000 miles, you want the swarf and new metal OUT. Then the break in can begin.
Nick
You first said all engines are “run in AT THE FACTORY”. Now you are saying “ALL ENGINES ARE TEST RUN” BEFORE INSTALL
A TEST RUN is a lot different from RUNNING IN AN ENGINE.
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ANY decent brand of commercially available motor oil will work just fine.
ANY brand of commercially available oil with the API seal of approval will work just fine for this engine: these engines are not highly -tuned F1 engines, but rather old school, fairly largely-clearanced street engines.
I stand by my assertion, backed up by quite a few thousand engines, that any decent commercially available motor oil will work just fine in it.
ANY commercially available motor oil today far exceeds the abilities of oils on the market 50 years ago.
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OK…semantics, word play…but OK…at the factory ALL engines are test run. Some are “run in” at factory, some partiallly “run in” , some not “run in” and left to new first owner. to “run in” .happy?
Nick
and some may be a little better or not than others…but for certain the formulas are not idendtical, as the formulations of ash, viscosity improvers, anti acid, anti sludge, friction modifiers, anti shear, anti heat…can be quite different. So save $12 bucks.
Nick
Perfectly OK to save those 12 bucks: you will not harm the engine when you do.
This whole hyperventilating about using the highest quality possible oil in these engines is nothing but smoke… and it ain’t oil smoke.
ANY oil with apropos ZDDP, irrespective of its cost, will work-- and allow me to repeat myself–perfectly OK.
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I’m not going to say whose opinion in this matter is correct or incorrect. I will say, however, that one should use the oil they are most comfortable putting in their car’s crankcase. That’s why I use Mobil1, and the added cost isn’t enough to reduce us to subsisting on cat food tacos.
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I’m generally as happy as a clam in high water. 
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