I'm a little afraid to ask, but I know I should so here goes. I have an '86 XJ6 w/ ~100k miles. I've been driving almost daily for the last few months since I got it. When I crank her up in the morning from cold I can hear a knocking sound for ~10 seconds or less, then it goes away. I have had the stakedown kit installed. I don't believe I hear this noise when starting any other time, wither hot or just warm.

Is this sound normal or should I be looking at something?

Thanks,

Eric

 

Sometimes a loose timing chain can cause a knocking sound. Usually more of a whir/grind...but you could check it anyway.

Does the oil pressure seem ok?

What weight oil are you using? And how cold is "cold"? If you are running 20/50 and the temp is freezing or below you might be starving the bearings.

Sometimes piston slap sounds like a knock.

*Assuming* it's a bearing knock or piston slap you don't have many choices. Do nothing or do an engine tear-down, inspect, and go from there.

Cheers
DD

 

Thanks for the feedback Doug.

Currently running 10W-30 dino oil, not synthetic. Cold was ~60 degrees F this morning. Oil pressure, after reaching operating temperature (and assuming my gauge is reading correctly) was 20 lbs/sq" at idle, 30 in city traffic and 40 on the highway.

Another question, what is normal operating temperature? Again, assuming the gauge reads correctly, it was ~90 degrees F on the way home today, coming back via the highway, and my gauge was sitting at the next hash mark to the right of 90 degrees C, so I assume that means 100 degrees C. Does this sound right to everyone?

Thanks,

Eric

 

Well the oil pressure seems OK. Just for the jeck of it I'd try 20/50 oil. Might help. The old XK engines like 20/50 unless the temps drops to near freezing.

Normal temp is 88-90ºC. On a hot days (like 95ºF) some increase is normal but at highway speed I wouldn't expect 100ºC. I wouldn't go into panic mode or anything but I'd consider having tha radiator cleaned.

Cheers
DD

 

I sympathise with your worries. The 1980 XJ6 4.2 I once had was quite noisy on start-up, I got clattering from the top end as the oil feed needs to get going and the head is on the end of quite a long oil feed line. I may have also have had piston slap.

Right from the start of production, these XK engines had to be selectively assembled by skilled fitters to make them as good as the designer intended, because Jaguar never really spent money on decent tooling to make the engine components accurately. This was maybe OK in the 50s and 60s, but I am sure that as time went on this aspect tended to be ignored, and the engines were not assembled as well as they once had been. So you may have a bit of piston slap before the pistons heat up and expand, but it is not really something to worry too much about. Take DOug's advice and use 20-50 oil, the modern "kerosene-like" oils are way too thin for old designs like the XK (designed during WW2 !!).

The lower timing chain can also clatter before the oil pressure gets to the tensioner. As regards this latter item, the feed has a little conical filter in the block where the tensioner bolts on, and this can get blocked up and slow down the speed at which the oil pressure gets to the tensioner thus causing a noise.

The reality is that the XK engine was regarded as very reliable and long-lived when it came out, but 100k miles, (your car !) was generally reckoned to be the time for an overhaul. This was perfectly OK up to around the mid-70s, but by the 80s was way too low as other luxury car manufacturers introduced engines and cars with much longer lives. Jaguar finally caught up with the AJ6 and AJ16 engines which seem to go on forever.

 

It's true that the XK engine is way too old to have seen modern precision technology but, still, they're a rugged old lump.

While an overhaul at a mere 100k might be done to ensure "as new" operation it is unlikely to be required for satisfactory operation, if you get what I mean. Do we overhaul an engine when performance has degraded a bit or do we wait until the old girl has heaved her final breath? There might be 50k-100k miles difference between the two ! :-)

I've seen countless XKs with 100k+ miles that were still running very well and obviously had tons of useful life remaining. Of course there are many variables that can reduce engine life on a case-by-case basis but to imply that an overhaul should be routinely expected at 100k isn't quite fair, IMHO.

One example, although not 100% typical, is my own Ser III. Although now under new ownership, it now has 160k miles. The owner reported using only one quart of oil on a 4400 mile road trip last year.

In Eric's case, if there's an actual bearing failure or piston slap at 100k miles, I'd honestly consider it an exception that could probably be traced to something in the history of the car.

Just my two cents :-)

Cheers
DD

 

I agree with Doug. Here is an analogy we use in the fire/paramedic service: "treat the patient, not the monitor". What we mean by that is just because there is a small arrhythmia, do automatically treat it unless the patient shows symptoms. By the same token, if your car has 100k+ miles on it and is running fine then you do not need to rebuild it yet. Wait for it to show strong enough symptoms that would warrant investing the $$$. Persistent routine maintenance will prolong that time frame.

 

I defer to Doug on this post, he has much more experience than me, and I am being a bit unfair on this magnificent engine that won Le Mans so many times. However, there were an awful lot of late year Jaguar engines that never got to 100k. This is probably down to lack of service and "tender loving care". I should have mentioned that I also had a Mark 2 2.4 litre before the XJ6. This was also a bit noisy when cold.

 

There *were* some duds, especially towards the end. Legend has it that the tooling was too old but Jaguar certainly didn't want to invest in new stuff virtually as the the engine was going out of production.

I think most of the duds were repaired under warranty and those that weren't are in the scrapyards. Those remaining on the road are the "good ones".

<shrug>

That's my take on it :-)

Cheers
DD

 

Thanks all for the feedback. Exactly what I was looking for. I will be changing the oil this weekend and see how that helps.

An update from this morning: outside temp was between 65-70 degrees F, I didn't hear any knocking, but maybe I missed it over some other noise.

My oil pressure readings were:
just after start up: 30 psi idle and 40 at pretty much any other speed.
warmed up (after ~25 mins driving): 20 idle, then 30 and 40 like I mentioned above.

My engine temp after ~25 mins of driving was in the just under to 90 degrees C range.

I'll monitor everything again on the way home. Another ~90 degree F day expected.

Let me know if these numbers are what you'd expect from a healthy engine or not.

Thanks again,

Eric

 

For what it's worth, I'm familiar with wrenching on older cars. My current line up consists of an '85 BMW M635 and a '56 Triumph TR3, along with the '86 Jag, but this is my first Jag so I am learning all the detail quirks of the car. Thanks for the help!

 

I religiously watch my gauges when driving. So far, my temp is at just under 90C when driving under normal conditions. My oil is close to 50 at just under 3000rpm and drops to just below 40 at idle. These numbers are after normal operating temps are obtained. I use 20/50 oil FWIW. One thing that I find interesting is that the voltmeter takes a while to reach "13" but my battery is fully charged. I am not sure if this is normal or due to age but the gauge seems to lag when I first start the car.

 

Lazy gauges are quite common...especially the voltmeters. I wouldn't give it any more thought.

Cheers
DD

 

Yeah, my voltmeter does the same thing.

I do wish my oil pressure were closer to 50 though...