Putting highly detergent oil in a heavily sludged engine is not a good idea. Steadily up your oil quality & halve your drain interval & the sludge will be suspended in the oil & flushed out unless chronic in which case stripping & cleaning is required.

Then run on premium synthetics & your engine will remain spotlessly clean.

Old Mercedes M112 V6 3 valve, twin plug per cylinder SOHC at over a million Km's (roller rockers on cam & hydraulic tappet tip. Still in service in Kuala Lumpur and driven hard in airport to hotel service. Serviced by Cycle & Carriage as advised. 15,000 Km oil drain interval. Prior to quadcam M272 4 valve per cylinder single coil on plug. Run on 229.5 Synthetic oil.

 

Glyn, Though it was in conflict with the monogrades they recommended, Jaguar did list 20-50 oils in their recommended lubricants charts in the mid or late 1960s. They aren't in my owners manual as it's too early, but I've seen them in later ones. They are in my service book. In view of the inconsistency with the 20/30/40 winter/summer/tropical monogrades, I can only imagine they (and other manufacturers) either saw the grades as a good compromise and/or didn't believe the VI improvers would survive very long.

 

They are not shown in my handbook or on plate. This is what is shown for S Type. See Mobil & Regent/Caltex/Texaco columns & note after table ~ I could not be more mid '60's if I tried. As best I can ascertain car was no 4 off the local line in Jan 1966. Never rconciled early licensing.

GTX & Duckhams were available in multiple viscosity grades e.g. 20W-40 which I ran my Alfas on until I realised we were selling them the adpack (our Oronite additive Division). Regent/Caltex/Texaco spell it out correctly,

 

It's not a great picture, a clip from a photo I found on the net, but it gives grades for Castrol XL and Duckhams Q.

 

All that tells you is that Jaguar were totally inconsistent. Mobil, Exxon & The Texaco conglomerate got the message and note comments below table of "advantages gained".

These engines were never designed to run on treacle unless you wish higher cold start wear (highly undesirable on an overhead cam engine}. Jaguar officially recommended a highest viscosity of SAE 40 & only in tropical zones. When the XK was conceived.

I think they just tolerated the Issigonis era due to what the average UK service station carried. The rest of the world did not.

What Jaguar intimates is if your engine requires rebuild you can run it on any old crap to shut the noisy thing up. Also a bit of an answer to their worn out tooling & sloppy tolerances.

 

In practice, would the difference between 20/40 and 20/50 have a significant consequence for an engine? Also, why are they so worried about 10/30 and others with the asteroid, in 'worn' engines?

Irrelevant, but I remember early Ford V6 engines that could shear their oil pump shaft if revved when cold.

 

An SAE 10W-30 Synthetic as Jeff runs & I have cases of in my garage for after run in is the ideal grade in a moderate climate. There is not anything wrong with 0W-40 or 5W-40 where summer to winter changes are more extreme.

A 50 would certainly slow oil flow at cold start accelerating wear. The joys of high VI synthetics. They flow more quickly because they are thinner at low temperature and thin less at operating temperature.

I imagine their worries in worn engines are Jaguars trailing clouds of blue smoke behind them. Not good for the Brand. Remember these were published in the pre synthetic era.

 

This clearly shows Jaguar's thinking for the XK engine which is why I return to it. Their intention was never to run thick oils in this engine. Running 20W-50 oils in this engine indicates a worn engine.("worn engines requiring overhaul" in Jaguar speak ~ meaning more wear at every cold start)

Peter's documentation that came with his car I'm sure echoes this.

 

Just for reference, this is from the last edition (1991) of the owners manual for the Daimler DS420, Jaguar's last car to use the XK engine.

To me there is some very odd recommendations. Why is 5W-40 only suggested up to an ambient temperature of -10°C, yet 20W-40 is good to beyond 40°C? Similarly using 20W-50 at -10°C is just asking for trouble.

 

JB ~ That's just a load of BS isn't it? or a misprint. Jaguar are really poor at that sort of detail.

There is also something on that plate I show above that no one ever notices where if ever getting viscosity right mattered. It is out of their pool of racing engines. XKC ~ 034. Why it shows a CR of 8 to 1 God only knows ~ endurance?? like Le Mans. Better longevity??

I also bang away at this for all the detractors that in their ignorance think that synthetics are "too thin" ~ which shows a complete lack of understanding.

If your engine is buggered it is buggered ~ rebuild it to modern tolerances with new parts. Plastigauge it etc. to ensure that tolerances are correct. Possibly why my engine is so quiet ~ too quiet I thought originally so I rechecked all the cam on tappet clearances but they are correct. 4 thou inlet & 6 thou exhaust ~ hot.

"Preferred Brands" my R'se ~ We sell them all the adpacks used. (Oronite our additive company). Nothing special about BP/Castrol. Good Marketers.

 

The grouping of the grades seems very strange.

It's fairly obvious that the draftsman who produced this piece of art stopped work for his tea and forgot about completing it. The bars without points on the ends should extend a lot further.

For a moment, I thought it might all have been aimed for some sort of match with Castrol products, but they don't coincide, so we can't blame Castrol.

The world seems a bit short of understanding on choice of oil grade and the compromises involved, especially for cold pumping, cranking, and circulation.

 

It sure does Peter. Seems when the small engineering team were around selecting monogrades they got it right.

 

Given it was 1952/53, perhaps the compression is 8:1 because there wasn't fuel with high enough octane to support 9:1? Just a thought.

It really is a shame that the oil recommendations that late (1991) for the XK are still out to lunch. I would have thought that there should have been someone in the Engineering department who could have given some technical advice? Or call Castrol and ask?

 

Yes at the pump you could well be right. High Octane fuel was certainly available for aircraft but for the humble motorist close to my birth you probably hit the nail on the head. I don't have a Le Mans etc. rule book from the era either. (oils maybe specified like modern F1 ~ locked down tight)

The document you show is actually a disgrace.

 

The first C types used 8:1 c.r. and later they used it when expecting poor fuel quality. That car has a mixed history. For a while, there were two XKC 034.

 

Correct! Most racing Jags had mixed histories. Where did you look that up. I'm interested to read. Google?? I was born 6 September 1952

There are very few people here that would understand ASTM D5293 Apparent Viscosity of Engine Oils and Base Stocks and ASTM D5133 test method used to analyze the flow behavior of engine oils at low temperatures.

 

Two XKC 034, I found from a quick Google. Even racing cars that have relatively simple histories often end up as bitsas. It's hard to believe, but its story includes being broken for spares.

For JB's oil chart, in it's last year's the DS420 was no longer a mainstream operation, a few people, mainly coachbuilders, so perhaps we should not be too hard on them...?

PS You're two and a half months younger than me.

 

That's close enough to be the same age Peter.

I will still continue to consider it a disgrace because I'm pretty sure it's just a carry over from the past and not unique.

 

I have access to various manuals, and that chart starts in 1987. Just for reference, the last XK engine in the XJ6 was 1987. The 1972 and 74 DS420 manuals simply list "recommended lubricants" by brand, and give no temperature chart. The oils range from 10W-30, 20W-40 to 20W-50.

Here is the 1980 -83 recommendations:

 

If you look hard to see the full stop in the viscosity rating after 20W/50 (?) and realise the temperature ranges don't align (lousy tech editing?), it makes a bit more sense. Yikes, it's hard work.