Checking oil engine oil level

There is mention on the forum of checking your engine oil level when cold and then there is SB168 which implies checking when hot. What is the consensus regarding this? I have a XK140

service bulletin 168 June 1955 …
engine oil level revised method of checking…XK140, Mark 7:engine
numbers B.5305-B/9999, D.1001 onwards, all engines.
On cars equipped with pressed steel sumps it is not desirable to
have the level of oil above the top mark on the dipstick when the
engine is hot and therefore oil level checks and topping up of
engine oil should be undertaken when the engine is HOT and not when
the engine is cold as has previously been our recommendation.

A later service bulletin on our 140’s specified that 13 qts of oil should be in the sump and that the dealers should remark the original dip stick to reflect the additional oil. Reason given was to prevent oil starvation on hard braking. Checking the oil level is best done on a cold engine. The oil will expand slightly as it heats which is bloody good!

Minor difference cold to hot…but the SB says HOT…and sumps should never be OVER filled. I am not aware of any later SB that reverses this one. The important issue is to be sure you have the CORRECT dipstick as there were several, with different lengths and marks. Any prior owner or shop could have replaced one with who knows what…so verify the one you have…several ways…by measurements, also a refill after a complete drain…with correct # of pints (quarts) …note US or Imperial spec, and then see if dipstick measures exactly as it should. Nick

For XK140’s, except the earliest ones, it’s 12.5 liters and the dipstick is C8781. I also note that I recently bought a sump plug from Mo** that has the incorrect pitch and will strip the hole if forced, so beware.

somewhere is a chart/article on dipsticks, with measurements from tip to add, to fill, etc and to handle There is an early Service Bulletin as well…to re-mark . …will try to find all to have in one place/one document.

Nick, you mean this one?

Please check my dimensions with the ones as provided in “Jaguar XK120/140 Explored” as there might be (minor) differences.

Bob K.


yes…wonderful chart…luv it…so…the SB that revises the full mark on the first dipstick C2348, simply…revises it to where it is on C2348/1 ? are the C part # actually on the dipstick?

Re " service bulletin 168 June 1955 …engine oil level revised method of checking…XK140, Mark 7:engine
numbers B.5305-B/9999, D.1001 onwards, all engines."

I couldn’t find any reference to engine numbers in SB168. In the 1960s my XK120 engine was replaced by a B series engine from a Mk VII. My interest is therefore whether I have the correct dipstick and am aware of the correct sump capacity.


In general there’s no number on these dipsticks, although I’ve once seen a number (stamped on the blade) on an XK 140 dipstick.

Bob K.

Great chart, Bob - thanks for that! I suppose the difference between the two types of XK120 dipsticks is due to the change from the full-length deep sump (oil pan) C2359 and the later stepped type? Curiously, my 120 has the early sump even though its engine number W2604-7 is later than the officially recognised change over point. It also has the early C2331/1 block which is supposed to finish at W2011, and the first-design intake manifold C2377, which should finish at W1250…


Here’s a photo of a dipstick that I have with a Mk VII block in a 120. I’ve no idea if it is the correct one for the engine which is a B series.

Regarding the “originality” of your engine (block), your engine W2604 (assuming the stamping is correct) is 593 engines later than W2011 which would be the last engine to have block C.2331 as the SPC indicates.
Engine W2011 was last used somewhere beginning September 1950. Your car was made beginning December 1950. In these 3 months about 625 XK 120s have been manufactured. So your C.2331 block might well have been used (like Rob says in the other thread) in the running production of engines. See also the “erratic” sequence of engine numbers in “XKdata” meaning there was no logistical control of engines during car assembly as they arrived from the engine department.
So we may assume that the use of blocks with the engine department had a similar character and in that respect a variation of 3 months is not impossible.

Bob K.

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As far as I can read the number stamped on your (C8781?), you have an XK 140 dipstick, which was also used on the later XK 150. This engine used the B-type head but the block remained unchanged, hence the identical dipstick.

Bob K.

I do have a related question. The 1959 3.8 engine I rebuilt for my MK IX came with an alloy sump which may be incorrect. Do any of you know if this sump has a different capacity? I want to make sure I have the correct oil level.

Thanks Bob. Yes, it’s C8781. It looks like what happened in the 1960s is the car ended up in a scrapyard (engine block damaged??). It was rescued and a B engine block from a Mk VII married to a 120 head.

That’s interesting and good to know, Bob. I didn’t know how literally one should take the cut off points for various engine parts. It seems anomalies are by no means unknown.


This is a much later (Sixties?) sump. I’ve no data about the correct dipstick for this sump. But if the block is still identical to the earlier ones, then the length of the dipstick and position of the marks shouldn’t have changed. But that’s only a (wild?) guess…

Bob K.

Do you have a photo of the bottom of the sump? Is it flat or ribbed? Does it have a kickout on both sides, or just on the right side?

Hi Mike.
My previous message included a photo. It is ribbed and has the kickout on both sides. I know it’s not from a 120 looking at the pictures in Porter’s book.

Looks like a Mk X sump to me.