Smoke, oil leaks, heat

Dear all,

I have a 1976 4.2 XJC (Canadian spec). My radiator fan having recently flung itself into the radiator (see thread Screech noise - fan or belt?), I have had the radiator replaced with a “high performance” aluminium model. At the same time the mechanic (not a Jaguar specialist, I did not have much choice, but a specialist in restoring older vehicles) took the opportunity to replace the leaky cam cover gaskets and tinker with the Stromberg carbs (previously running a bit lean, resulting in a flat spot until really warmed up).

Saturday morning I drove 40 miles of hilly country roads without incident, and no more flat spot, although when entering town and an underground car park at the end, the indicated engine temperature approached the “a” or “normal”. Ambient temperature high 20s centigrade. This was a faster pick-up in temperature than I had experienced before. I have air con but was not using it.

On the way home, I took the motorway and during the long upward slopes at approx 70mph noticed brown / black smoke behind and at the same time a drop in indicated oil pressure towards zero. Previously it would be around 20psi or so (it’s never been high). The smoke would disappear on the downhill stretches but pressure stayed low. Smoke came back on the uphill slopes. Engine temp displayed a bit above the middle of the gauge, but well within “normal”.

Stopped the car, temp rose to the “l” once stationary, observed oil leaking around the rear of the engine (not the cam covers) and burning off, and some residual brown smoke (not blue) from the right hand exhaust.

Didn’t want to risk it, so had the car towed. No other issues, no flat spot, that’s what I know so far. I don’t know if the mechanic filled the coolant using the correct procedure (he used a mix of coolant and water though, previously I used pure coolant).

I am surprised that the temperature rises more readily with the new radiator. I am using the same 88c thermostat. My mechanic claims that that is a feature of aluminium radiators versus steel but it is not overheating. He also favoured installing electric fans but following much debate I asked him to stick with the original set-up (including new thermal clutch), reasoning that it should work perfectly well if properly installed and I did not fancy upgrading the alternator to feed the fans.

So I am seeing views please on the issue here. Is it running too hot? Too rich? Why the sudden oil leak? Do I stick with the mechanic who by now knows the car somewhat, or is it better to start afresh with someone else?!

Many thanks,

Nick Hill

XJC 4.2 Series II (1976, Canadian spec)
Paris, France

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Coolant+water is better at transferring heat. That is good.
The radiator does its job. Good that you stayed with the original setup as far as possible.
What do coolant and oil look like?
Oil smoke if from the exhaust is blue, water white, fuel black. Maybe he set it to rich; talk to him on the phone… chances are he will set the uphill overfueling right in no time at all.
I wouldn’t mind the temperature. Rising temperature after shutdown is also normal.

The oil pressure reading(!) and smoke should not have anything to do with each other unless something unlikely is going on. Check the oil level and consistency, have the guy set the carbs again and keep an eye out for the oil pressure. A few seconds without won‘t kill the engine. You will hear it clatter when the oil is really gone, then stop.


in fact, unless you used pre-mixed or ready-mixed coolant before, it is way better to use the correct mixture instead of pure anti-freeze. Also, the standard viscous coupling + metal fan setup should carry sufficient cooling capacity for use in France.

At high 20°C ambient temps simple use of the engine (as opposed to extended use such as in mountains, racing etc.) should never take the car to water temps above the t-stat temp. So “n” would be right, “a” is too much for use outside, but does occur following spirited drives ending in city traffic like in your underground car park.

Second issue is the smoke/OP thing. David is right - there’s no sign of a head gasket failure (white smoke) and no sign of combusted oil (blue smoke). Loss of oil burned off on the grimey exhaust might lead to brown/black smoke. “Level” of the car - ie going up- or downhill - might take the oil further back where it meets the exhaust …

Even so, loss of oil and pressure would concern me a bit more than David. While the OP guage certainly is no precision tool it usually does its job well to monitor changes. Maybe start with the sender (there are two: one for the idiot light, one for the OP guage), check the connection, maybe replace it. Jaguar specs call for 40 psi at 2000 RPM. The drop to almost zero is kind of normal, but should occur only when idling and with fully warmed engine.

An OP drop on an engine used in a regular manner indicates either a failure of the sensor/guage or a serious problem in the oil circuit. To avoid more damage check oil level and quality regularly. How big are the losses? Are there strange smells (sweetish from coolant)? With a leaking master cylinder brake liquid could be drawn into the engine.

Does the brown smoke really come from (only) one end pipe? The y-pipe supplies both end pipes from only one tube. Has your exhaust system ever been changed?

I’d first suspect the oil pipe mounting from the oil filter basis up to the cam galley. If it leaks the oil pressure will react and the oil will run down at the back of the engine.

To check the carb setup take the car to a gas analyzer. They will tell you whether it is overly rich. German TÜV charges 80 EUR for a test, but it is money well spent for peace of mind (even though you can’t provoke high load pinging)

Good luck and keep us posted


75 XJ6L 4.2 auto (UK spec)

Make sure the dipstick is fully installed and not hanging up, the mechanic may have overfilled the sump and travelling uphill oil will gravitate to the rear and exit out of the rear crank seal.

The key word here is “…indicated…” is this an electric gauge of mechanical? The senders for the electrical pressure gauges have a short life. They often give low readings.

Your original radiator would have been of brass & copper construction. Aluminum is actually an inferior heat transfer material to brass/copper, but it is stronger, much lighter and much less expensive as a raw material. The downside is that it is generally more difficult to repair and it is not anywhere near as corrosion resistant. To get the same heat transfer from the hot engine coolant to the cool air stream aluminum needs either more surface area or more air flow.

As a practical matter, you should always use an antifreeze solution mixed to provide the freeze protection you require. Antifreeze solutions contain important corrosion inhibitors. Plain water is the best heat transfer fluid, but it will slowly destroy the engine via corrosion.

Black smoke under load, particularly going uphill, is indicative of an overly rich mixture. If your tuner changed the mixture to eliminate your flat spot, it may now be too rich under load. Oil smoke is blueish or white. White or blue smoking on coast down is indicative of leaking valve stem seals on the intake valves, where the high manifold vacuum generated with the throttle closed under coast down can pull oil past worn seals. There are no stem seals on the exhaust.

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Thanks all. So regarding the various questions:

  • both exhausts were smoky
  • not sure what kind of gauge it is, I think electrical
  • I think exhaust system was changed a few years back under PO so is not ancient
  • have not looked at coolant although oil looked ok

I am hoping that the alu rad was not an expensive mistake!!



  • both exhausts were smoky
    They are not 654, 321: they share a short run of exhaust pipe or have an X pipe. If you hold one shut the engine will keep working. Both tail pipes emit the same exhaust.
  • not sure what kind of gauge it is, I think electrical
    Yes, it is. If the idiot light doesn’t come on it is diagnostic but never trustworthy.
  • I think exhaust system was changed a few years back under PO so is not ancient
    Doesn’t matter.
  • have not looked at coolant although oil looked ok
    That’s a plus. Only look at coolant when cold. If the oil pressure drop was to the outside and read on the gauge the oil would be long gone. I suspect the sender here. The guy set the car too rich, and since all is new you’re now overly sensitive and worried, by the way: Aluminium is just fine. Keep being careful but don’t worry.
    Besides, if I count how often my dying engine ran low on coolant and got hot, or lost oil pressure braking downhill… cats have many more lives than just nine. Just keep an eye on the oil light and another one out for interesting and provokable misbehavior.

It sounds like you have more than one issue but being a 76 Canadian car you probably have the water choke versions of Stromberg carbs. They have a thermostatic device that is directly affected by coolant temperature from a coolant line as well as other systems.

These can be difficult and require careful setup for the water chokes to function properly. It sounds like your mechanic’s tinkering has resulted in a rich condition due to whatever he did to the system. Strombergs normally have very little mixture adjustment in the normal sense to keep the emission controls from being thrown out of whack. I would have the mechanic readjust them using a manual specific to those carbs. If he can’t, find a new mechanic that knows the ins and outs of emission carbed British cars.

Also I can tell you that I see many water choke Stromberg equipped cars that people ‘de-smog’ by simply disconnecting the air injection system. The carbs don’t like that either and will idle very rich creating other problems.

This system really needs to be intact and properly adjusted to work the way it was designed.

Oh and a final thought, this car should have a vacuum-retard distributor capsule that should be connected to ported vaccum on the bottom of the front carb that only functions at idle. Sometimes unknowing mechanics connect it to full manifold vacuum which means the ignition is always retarded - This will cause overheating.

I would look carefully at what sort of ‘tinkering’ was actually done to the car - just changing to a new Aluminum radiator (a good thing) and gasket replacement wouldn’t cause all these issues.


Hmm interesting, thank you.

It has a tendency to race in Park or Neutral, 1200-1500 rpm. This drops to something approaching the correct engine speed when Drive is engaged, maybe 750-850.

My feeling is that the set-up is not right, it has never been right since I bought it. Initially it was way too rich, didn’t even need the choke, then a bit too lean, now too rich again. Mechanic says the Strombergs are in poor shape and should be swapped or reconditioned at a cost of €800-€1000. But would it be better to switch to a more conventional SU set-up…?

I am not familiar with the water choke or air injection. But for the avoidance of doubt the AED was removed years ago in favour of the manual choke like pretty much every other SII.



1200-1500 is way to high Nick. If indeed you have manually converted water-choke carbs I’ve found they can still be problematic because yes, it removes the thermostat coil element but they still have other things going on in them that require proper setup. If your mechanic is unfamiliar with them and just started twiddling things he probably did something he shouldn’t have. There is alot to the whole emissions system in British cars of that vintage that can be an issue if things are just disconnected so maybe a good starting point would be to assess the whole system to see what is there and what isn’t.

Living in the US I’ve been dealing with them on Jags and other cars for years. Honestly, those water choke carbs are a huge pain and you would do much better to go to either SU’s or even the earlier Stombergs that just had manual enrichment devices. I personally wouldn’t bother to recondition them - a used set of earlier, manual choke Strombergs are cheap and you can get them running just fine.

But back to your original issues. I very much doubt there is some issue with the radiator and in fact I have multiple cars with aluminum rads and have driven around alot in really-hot South Florida without issue. One thing that could be a problem is if the mechanic did something to the thermostat. If he installed one of the wrong configuration - without a foot to close off the bypass - that would definitely cause an eventual overheating situation. Not apparent immediately but would show itself with some motorway driving for sure. When I first got one of my 72’s it had the wrong kind of thermostat as described which I didn’t know yet because I just got it. Drove it for a little shakedown and it was fine and actually running a bit too cool for a good 20-30 minutes on normal flat roads. Once I got on the highway it started to slowly get quite hot. Pulled off and oil pressure was super low and it was hot! after cooling back down all was okay again and when I finally got it home, opened it up, found and fixed the incorrect thermostat - the car never overheated or had oil pressure issues again.

I would be absolutely sure he put in a thermostat of the correct design. One quick way to see it without opening the system: does it take a long time to come to operating temperature when you are just driving slowly around town or idling? That’s a telltale sign in this car. Maybe get the mechanic to tell you what model number thermostat he installed and see if you can see an actual picture of it by googling.

If your gauge stays normally around 20psi at motorway speed and the car has not exhibited any other oil related issues I would think your gauge or sender isn’t quite right. A little too much heat in the system may be enough to get an already low-reading gauge to zero - if you don’t hear alot of horrible clattering it’s got some pressure.

The brown/black smoke is obviously over-rich air/fuel mix. You may have more than one thing wrong but I think you definitely have a problem with the way the carbs and emission systems are setup. That may be the best place to start assessing what is going on.


Ok thank you all. I didn’t think he had touched the thermostat but this is something I need to check. In any case, I reach operating temperature on the gauge promptly, within 5 mins of driving I would say.

I am paranoid about overheating given that one of the key tasks befalling this car is to survive a traffic jam on the motorway in 35c heat.

So I need to have the mechanic

  • check oil and coolant for signs of contamination
  • identify source of oil leak
  • check oil pressure senders and replace if necessary
  • check coolant correctly filled and thermostat
  • check sender for radiator
  • check vacuum at distributor capsule and PCV
  • check oil pipe mounting from oil filter to cams
  • check emissions for mix
  • check ignition timing
  • try to get carbs set up correctly; failing which consider replacing with earlier Strombergs or SUs

Unfortunately I am not 400 miles away so not much I can do myself.

Thanks again


All things considered on the Alu rad, despite the thermal conductivity matter, it’s likely as not that your old copper/brass one was a bit compromised with silt I would expect. I would get your engine back within bounds of normal operation before you make a judgement about the rad. I put an Alu rad in my Mk2 and the car behaves much better than it did with the original copper/brass unit (tank split after 55 years). Paul.

So, update from the mechanic.

There was air in the cooling system. He does not seem worried about that now that it is properly filled.

He actually does not think there is much wrong with the engine itself. Maybe running a bit rich as others have said but nothing too get too worked up about right now.

However, there was oil all over the place. He has had the car up on the ramp and identified the lip oil seal gasket seal (I think – in French, “joint spi”) between the engine block and gearbox as the culprit. He reckons this explains the loss in oil pressure. At any rate, the engine is not usable right now for motoring purposes, such is the rate of oil loss.

His proposed solution therefore is to get the engine out and replace the seals. There is also a leak of ATF from the gearbox itself which he was unable to locate last time and appears to be a bit random, possibly linked to the position at which the machinery stops (sometimes it does not spill a drop while parked up, but sometimes a lot). And a further leak from somewhere else down there.

He is estimating the procedure at 30-40 hours of work. This is not a negligible cost. It seems there is little choice if I want to keep the car on the road.

But before I give the go-ahead, any observations on the above welcome.

Many thanks,


If he is referencing the rear crank seal, that would not cause a low oil pressure issue.

I would replace the bypass valve and while the engine’s out, do a bearing check.


Low oil level would be indicated by a drop and recovery after hard braking especially downhill.
Were I doing the work 30-40 hours would be quick but it’s up to you; the oil leaks if that bad: do it (but what else while the engine’s out? So much to do!)
I assume you don’t want to do some of the work yourself? For a full engine and transmission gasket set and the fluids you would have material costs of around 200€ but it would take time and parts of the work are hard. Just make sure he promises that the engine will run reliably and leak-free (ish) after he’s done.

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Thanks. I would love to do the work myself but (1) no time; (2) don’t have the skills.

Anything else you would recommend doing while the engine is out? Is the received wisdom to deploy the rear seal converter unit?



Indeed, completely unrelated.

Does the 4.2 have the two piece seal?
If so, doesn’t reverting to a one piece seal requires work on the crankshaft?
Can’t it be changed with the engine in situ by just removing the transmission?

Yes the 4.2 does have a two piece seal.
It can only replaced when the crankshaft is out, that means engine out, and gearbox removed.
There is a modification on the market to get a lipseal, but involves modifying the crankshaft, and a new seal housing ( expensive )
It has nothing to do with the oil pressure.
Low oil pressure is mostly worn bearings ( crankshalf, bigend bearings )

Are these the right seal parts?

This seems to be the conversion kit but I am not sure I want to embark on this unless it is really the benefit from the marginal effort is worth it.

If it’s a rope seal wouldn’t a leak indicate a fault on the PCV system and not at the seal itself?

When Nick experienced a massive leak was when his engine overheated, combined with a loss of oil pressure.