Which oil and additives for a old engine

Hi everyone.
Looking for some info on which is the best oil and additives to use on my 3.8 xk engine. Story is the head has blown but the head was rebuilt less than 1000 miles ago. After removing the head I found the head bolts to be too slack. Most likely the cause of the blown head gasket. Just getting the head skimmed but in the mean time I need to remove the creamy oil from the remaining engine. Do I remove it now while the head is off or wait till I can warm to engine up to remove it.
Best cheap engline oil to use for flushing out
Best quality oil do use after its clean out
And best additives to use as engine isnt brand new so I want to look after the block ect
Thanks guys for any help

Any good-grade modern oil, changed regularly, that’s on sale, will suffice.

Welcome to the club!

You’ll get aaaaaall kinds of breathless replies about the dangers of low ZDDP oils: on a stock XK, with its low spring pressures, I believe it to be vaporware.

My 3.8 and my Rover engine, combined, covered 10s of thousands of miles using modern low ZDDP oils, and have exhibited exactly zero. issues.

Modern oils are all lightyears ahead of what was the best, when the car was new.

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Cheapest oil to flush it out, whatever it is, even Diesel or atf would work (I’d use the oil from an oil change and just run it for a few minutes) then 20W50 for large machinery and with frequent changes. Doesn’t need to be anything fancy. I would remove the drain plug now and let it drip out.
The 3.8 are excellent engines and bulletproof. Don’t worry about age and miles. Some ridges on the bores are okay, unless you can feel them. Any issues while driving?

Were the head bolts retightened after some driving? Is the head warped or damaged by the blown head gasket?
Welcome to the forum!

Thank you for the warm welcome. The car is new to me but the engine I’ve known for 20 odd years. Now the engine is in my care I want to treat it and take extra care of it.
One concern is sight side to side movement on piston 6. But it is a TDC while the head is off so hoping it’s just slack in the bore at the top. No ridges on the bore and the head was rebuilt and is now being skimmed so fingers crossed it all good.
Engine did run and sounded fine

Oil can’t fix a rocking piston but I wouldn’t worry about it. Especially if it ran fine.
If you want to treat the engine well, don’t let it idle too long, drive off gently until it is warmed up, then drive it hard. Drive long distances regularly, and change the oil, filter and coolant frequently.

Was the head retorqued after some miles?
The head gasket settles down a little with some running in and the head bolts will lose tension. It has to be retorqued otherwise it might eventually blow. Could that be what happened?

I think that’s the reason it went as the guy sent it off for paint and it came back with a fair few miles on it.

I’ve got a 4,2 l XK engine in my Stype from 1964, and the oil pressure is good when I start with a cold engine, but a bit too low when the engine is hot, about 27 psi at 3000 Tr/mn. I use actually Gulf 20W50, may I try an another oil, i think of a synthetic one for example to fix this ?

If it were mine the first thing I would do is get a known good mechanical gauge and fit it where the electrical sender is and verify pressures with that. These Smiths senders can often be inaccurate.

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drain it now…flush it with thin weight oil. For running…while many say zddp is not needed, and that may be true, there are plenty of good engine oils that DO HAVE the proper parts per million of zddp in it.(1000-1200ppm) .so why not use those. It is a flat tappet cam…yes low spring pressure. Still…one oil on shelf without zddp, and…one with zddp …I select the one with. I choose Mobil 1 15-50 but there are others. As to old oil…the answer is no…combustion byproducts of acid etc do harm, so change it at least annually. As to old engine…keep rev limit low…3500? 4000 tops?

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Yes. I‘ve seen acid eaten bearings. The cars aren’t driven often and the oil isn’t changed because it’s still looking good and has low miles…

The S type engine may just be tired?

Yes, I have forgoten to mention that I have already replace the Gauge by a mechanical one, to be sure of the value.

My experience of low oil pressure in XK engines is to look first at the gauge, then the pressure relief, then the pump and last of all wear in the crank.

What’s the best oil depends on the history of the engine and what you do with the car. If the engine is recently rebuilt and the sludge traps carefully cleaned, there’s nothing better than the modern synthetics. That’s especially true if you plan on decent mileages and some long tours. If the car is doing only a few hundred miles per year, visiting a few car shows etc, regular oil changes (minimum once per year) are more important than what oil you use. You might then want to save on the cost of the oil and use a good quality mineral oil from one of the major oil companies.

William Lyons is often accused of penny pinching, but he didn’t save up on drilling holes to circulate oil around his engines. The valve gear has a more than adequate supply and I don’t see the concerns about absence of ZDDP.


Available at Walmart in 5Qt. jugs too.

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since it is available…why not use it. This one or the others like it. I rest my case.

That’s what I use in all my old cars.

With the low spring pressures of an XK engine, neither am I, and on two other flat tappet engines that I had experience with, both of which went over 200,000 miles, I just used whatever was on sale. The tappets and cams looked like new!

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Hi, Just another thought occurred to me. Maybe the head studs might have been bottoming out with the inside of the acorn head nuts before actual torque was achieved. I have had to remove material from the inside of aftermarket acorn nuts to not interfere with the studs while torquing the head.

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Honda actually had a recall with, IIRC, a 400cc twin motorcycle. Acorn nuts bottoming on excessively long studs gave a correct torque reading and leaking head gaskets.

The “new” acorn nuts I got had very poor consistency, with a internal vernier depth reading showed over .040" variation !

I was extremely lucky to catch this, as one of the nuts you could slip a .002" feeler gauge after a head gasket change

I subsequently found out it was cheaper to have my original nuts re-chromed locally