Warm compression numbers!

Even though Kirby said it couldn’t be done, I got warm compression numbers! (I cheat because I don’t have an AC compressor.)

Car was 190F coolant temp when shut off. It took me only 40 mins to remove throttle pedestal and all plugs, and rig throttles to be wide open, and remove fuel pump relay. Then took me 20 mins to collect numbers. Engine coolant temp was 160F throughout test.

Oh, and I’m quite happy with my numbers!!! 215 - 225.

(1988 xjs V12 with about 50K miles)

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Greg,
Your post got me curious, so I looked up the cold compression check numbers when I restored the engine bay of my wife’s 1990 XJ-S convertible (5.3L V12 with Marelli ignition) in April 2017. At just over 126k miles the cold compression numbers ranged from 204-215 PSI which are a little lower than yours, but still decent absolute and relative numbers (plus or minus 3% of the 211 PSI average). If this engine was warm like yours I would expect the numbers to be a bit higher. I did this compression check after I adjusted the intake and exhaust valves because 12 were outside the 0.012 - 0.014 inch spec. I adjusted them all at 0.013-0.014. All of the ones that were out of spec had closed up, one down to 0.009.

I remember being thrilled with thevresukts at the time because it meant that I didn’t mess up anything when I adjusted the valves. That was a big technical challenge for me even after adjusting valves many times in my I6 cylinder Jaguars.

Paul

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Yeah, it’s a super nice feeling seeing high readings on a compression test, especially for such an old engine.

My cold numbers were in the 190s back in October, although that was when I first got my XJS after the engine had been sitting for 7 years and was barely running. That’s why I did a re-check, now that I’ve got things tuned up and driven about 1000 miles.

Those are good cold numbers, Paul, especially at those miles. I’m realizing that these V12s are built like a tank. Besides the misc weaknesses surrounding the engine (like ignition, cooling, etc), the valves and rings seem to be high quality? Most cars I’ve owned, with that kind of mileage or even age, the rings and valve stems start burning a bit of oil. Knock on wood, since I changed my oil three months ago, it hasn’t budged on the dipstick!

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Greg,
I keep track of oil usage between oil changes on all of our Jaguars. Our I6 cylinder 4.2L XK engine equipped Jaguars use about 1 U.S. quart for each 300 miles driven and the two 5.3L V12 Jaguars use about one quart for each 1,200 miles driven.

Paul

Burning only? Or does that include leaks like RMS?

Greg,
Those oil consumption numbers are from normal usage. I don’t have any Rear Main Seal oil leakage problems.

Paul

Surely a misprint Paul - 300 miles per quart for the 4.2 litre cars?

Frankie

Frankie,
I will review the oil consumption records for my 1969 E-Type, 1984 XJ6 Vanden Plas, and 1987 XJ6 Vanden Plas all with the 4.2 L inline six cylinder XK engine and post back their specific numbers. In the meantime, what oil consumprion are you experiencing in cars equipped with the 4.2L XK engine and what are those models and years?

Note, I am talking about the Jaguar XK engine developed right after World War II and produced from about 1949-1990 and not the 4.2L V8 produced much later and installed in more modern Jaguars.

Paul

About what I’ve seen most XK engines do: Tweety, even after his rebuild, did 500-600/quart. I was happy!

Ouch! Is that valve stem seals or piston rings?

IIRC, the factory spec was just about that: in Tweety’s case, he had within-spec bores and pistons, but not perfect, and intake seals that didn’t seal that well.

Plus, the rope seal did its share!

Paul,
Yep, those I6 Jaguar XK engines use oil and were developed in a time when that was OK and didn’t matter much. I think that Frankie must have been thinking about the 4.2L V8 engines produced 50 years later.

Paul

I know, and how times have changed!!

I clearly remember most cars consuming oil, and the general attitude was, “Meh,”

Now, when a car uses ANY oil in their 5000-10,000 change interval… hair on fire!!!

I have a 1971 4.2 litre 6 cylinder XK engine in a series 1 Daimler Sovereign with about 65,000 miles (probably genuine) on the clock. AFAIK it hasn’t had a total rebuild, but I see evidence that the head has been overhauled at some time. I have never bothered to check the oil consumption (but will keep records form now on!) but I top up probably once between oil changes which I carry out every 3,000 miles. AFAIK the original Jaguar estimated consumption was 900 miles per UK pint.

The range of my S1 is about 300 miles on two full tanks if fuel, so if I was needing a quart of oil every 300 miles I would be topping up at every fuel stop. I am assuming one US quart is about 1.6 Imperial pints (UK).

Frankie

Greg,
I would attribute the relatively high Jaguar XK engine oil consumption rates to the technology that was available in the late 1940s when that engine was developed as well as the low price of oil and the lack of awareness of the environmental issues at that time.

Paul

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Or just leakage out onto the road?

In Australia it’s illegal to leak oil. Their contention is that it creates a safety hazard, coating intersections with oily pavement. I’ll bet when they passed the law, though, a few car companies had to rethink their gasket designs.

My 1957 Jaguar MKVIII with a 3.4L XK engine has an aluminum tube leading from the front crankcase breather port to the left front wheel well where it vents hot oily crankcase gases. The engine was designed and built before intake valve seals were used. I am still working on it’s restoration and it hasn’t been driven since 1975. But someday…

Paul

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Yeah, even racing programs don’t permit that stuff. Gets the track oily. They’ll require you to have a “catch can” on the end of that line.

Frankie,
I reviewed the oil usage for the six drivable Jaguars (1969-1990) that we have owned for at least a decade and driven each for tens of thousands of miles, one for over 100,000 miles.

My original estimates in a prior post were pretty good. The three 4.2L XK engine equipped cars got about 300-400 miles per U.S. quart (1.66 Imperial pints) and the two V12 cars about 1,200-1,500 miles per quart.

I do all of the oil changes myself, and use 20W50 brand name oil. The 4.2L engines get their oil changed every 3,000 miles or 1 year whichever occurs first. The V12 cars at 5,000 miles or 1 year whichever occurs first. All these engines have roughly 100,000-200,000 miles on them. Four of them are required to pass California Smog Tests every two years and they all pass with numbers well below the limits, often well below the average for cars tested.

Please let me know if you have any further questions.

Paul