Even bottom of the food chain 911s like the 912 and SC are worth something and the owners are extra serious.

At the end of the day no matter what you have under the hood you’re still driving an XJ, it’s not a desirable vehicle to most people.

 

The reason your 4.0 works is the six is seriously lighter than the V12 yet puts out nearly the same amount of power as the V12. ( the advantage of a modern 4 valve head ).
Since it’s about equal to a Chevy 454 in power output ( which only has 230 SAE Net, but seriously more than a 350 with only 160 SAE net )

The smoothness and torque of the V12 has to be experienced to understand. While I love V12’s I wouldn’t recommend One to you. Since you don’t do your own work you would be at the mercy of the mechanic and they have to make house payments too.
For those of us who do our own work the V12 is affordable and not particularly more complex. Once you understand how a one cylinder works, it’s just 12 instead of 8 6 or 4.

Yes the quality of early V12’s was poor. That’s because Jaguar was loosing over 100 million dollars a year in the early days. Once Jaguar joined BLM things got worse instead of better.

With Fords investment great strides were made in quality.

 

I sold my 81 SC last year for $28k, about 3x what I paid for it 8 years earlier. It was in very good condition but was still a 40 yr old car and had a lot of oil leaks.

This clown has a POS 78 for sale right now asking $22k. So outrageous I had to email him. He said he just sold the engine for $20k. Dear lord I hope no fool paid that.

https://greenville.craigslist.org/ct...219670916.html

 

I recently saw two V12s in BRG and very nice cars on ebay. Had I not already purchased mine, I would have considered them and perhaps taken a chance on them. I have a very good mechanic who is honorable and trustworthy, but again he is not a Jag or V12 expert. I will say that my 4.0 already runs warm enough here in summer with AC on, which I have learned is just how they are, so my main concern would be even more of a temp issue. From what I've read on here heat seems common to both engines. It's manageable on mine, and perhaps others, but you do not live in SC where we see mid 90s for months. Any other car engine temp is not something I even have to think about, and would rather not.

 

This is so true...a more modern S/C Jag V8 is much more like an upgrade rather than a Chevy lump, plus at least as powerful, or more, as any good Chevy lump is. But, with either choice, you want to do this with a face lift car for starters (i.e. 3.54:1 vs. 2.88:1). Back, when the V12 cars were dying like flys (70's and 80's here in the USA) the Chevy V8's were pretty much the only option, but nowadays, with so many accident destroyed, modern NA and SC Jag V8's available is a no-brainer and you keep your baby 100% Jag.

 

The upgrade really is only for those who insist on 500+ horsepower. The reality is that there are plenty of good solid V12’s with nothing wrong except some hose connection or simple sensor.
OBD2 didn’t come to Jaguar until after the V12 was out of production. Without the ability of having the car tell them what to repair owners and mechanics gave up on otherwise nice cars.

A few enterprising mechanics retrofitted the carbs of the earliest Jaguars for the sake of simplicity and found a lawn mower simple solution that still produced 10% more horsepower than a Chevy 454.

For those who insisted on retrofitting a small block Chevy they found that a stock 160 horsepower V8 didn’t offer anymore reliability, or Or as much power than the V12 did. In fact for the Chevy 350 to make the net power the V12 did required serious and expensive modifications to the Chevy, further reducing the reliability of the Chevy.
Further, HVAC and other issues with the Jaguar continued at the same pace. So spending $20,000 on a car purchased for a few hundred really doesn’t make sense. Far better off spending that $20,000 on a newer faster more powerful Jaguar that has benefited from Fords massive quality control investment.

 

You shouldn’t have to worry about temps on the 4.0. Should run in the high 80s mid 90s no matter the ambients.

 

The 4.0 with AC on, on a summer day with temps in the 90s, will begin to creep up uncomfortably on the temp gauge when idling in traffic. Maybe past N is considered ok. I’ve read enough on this forum to know there are many others with same concern. Consensus is past N is ok on these cars and considered normal. How much past N is not clear but I don’t want to find out. I’d feel better if the temp needle didn’t move at all when idling on hot days. No need to tell me to recore the rad or some other nonsense. It’s how it is and others concur. Less of an issue with AC off.

 

Working as intended. That’s why the X300 XJ switched to a “dummy” type gauge to solve the problem of overly concerned customers. With that setup it reaches moves to normal at 70ish and stays there till 100C.

All cars have this setup now for pretty much the same reasons.

 

So that's what I have gathered. Question is - how much past N is ok? And just how far will it go if I continue to idle? I'm too scared to let it get too far past N.

 

Water boils at 212 degrees when you add coolant it increases approximately 10-20 degrees depending on concentration. Then you add pressure you continue to increase the temperature before the coolant boils.
Why all the technical stuff? Because that’s your answer. As long as it’s not boiling the coolant is pulling heat from the engine.

To keep it simple? When the needle gets all the way to the right you should do something differently. Before that be aware but stop worrying. If Jaguar thought you you’d be better off knowing exactly what the temperature is they would put numbers on. If you want to know in spite of what Jaguar engineers determined, buy a infrared digital thermometer and aim it at the top radiator hose and then at the lower radiator hose. If there is a difference the radiator is doing what it’s supposed to do. The water pump is doing what it’s supposed to do. The coolant is doing what it should.

 

if it’s an AJ16 just use one of these.


https://www.ebay.com/itm/153187642003

 

Knowledge will end your fear. Buy a $20-30 digital infrared thermometer off Amazon. Wherever the red dot is it will tell you what the actual temp is. Aim it at the upper radiator hose to tell what the temp is coming out of the engine.

Aim it at the lower radiator hose to tell what temp it is going in.

You can aim it at the exhaust manifold one cylinder at a time and confirm all 12 cylinders are operating. ( it will shock you how many can be dead and still have a decent running engine).

 

OR switch to Evans waterless coolant,, does not boil till 375F , eliminates head temp HOT spots that contribute blown head gaskets!
ron

 

What is the downside of Evans waterless coolant?

 

Extremely poor heat transfer, flammability and inferior freezing protection when compared to 50\50.

https://www.norosion.com/evanstest.htm

 

well my experiance with Evans is with a hi boost Mazda turbo rotary engine ,Dynod close to 500HP, 12 yrs in the car, NEVER an overheat, remote temp digital gages!
finally took the engine apart, and showed absolutly NON corossian, amazing inside cooling jackets COMPARED to water!
after reading that report from a Chemical company , i say THEY are not 100 % accurate, to many contradictions!
also they dont say why the Evans coolant was 1st developed, for the US Military, for cooling the Blackhawk helos, hydraulic systems,(not the engines they are shaft turbine units)!
ron

 

And...I couldn't disagree more. That's essentially saying that 100% of the character of an XJS is tied up in the engine and engine alone, when the V12 was actually shared amongst other Jaguar models and all XJSs didn't come with the V12.

I bought my XJS specifically because it had already been converted to a V8. I won't go into all the reasons why—they've already been discussed. My car has the same Jag styling as one with a Jag engine, the same Connolly leather interior, the same wood, the same incomparable ride...almost all of the key elements of what makes a Jaguar a Jaguar. Yes, the engine is different.

I also love 80s Pontiac Trans Ams. The fastest one made was the 1989 Turbo Trans Am, and it came from the factory with a Buick engine. All other 80s Trans Ams came with Chevy engines from the factory. When shopping for an XK8, I compared it to the Maserati 4200 GT, which came with a Ferrari engine from the factory. Are none of these cars "real" because they used engines from another brand?

Can we all admit that the engine is a PART of the car's character, and not the totality of it? I mean, NO ONE tells the guy that swaps in bigger sway bars, stiffer springs, and a manual that by altering the factory suspension from Jaguar's original compliant ride that his car is no longer a "real" Jaguar. We know that the legendary, comfortable/compliant ride is part of the car's original character, but in no way comprises the totality of its identity. If it's changed, plenty still remains to appreciate of the original car's character. Same when the engine is changed.

 

To each his own. But talking any GM product is just badge engineering and a moot point. A Trans Am engine is no different than a Buick, Chevy, GMC or other. They're all essentially the same and from the same mfg.

But a Ferrari with a GM 350 engine is NOT a Ferrari. It would be a laughing stock. A sad joke. A Joe Dirt Special. Is a Pontiac Fiero with the most correct Ferrari body kit somehow a Ferrari? No one cares about Ferrari (or Jag) springs or sway bars. Ferrari = Engine. So yes, pretty much 100% of the character of a Ferrari is tied up in the engine. Same with a Porsche. Alfa. And many others.

There's a very beautiful, impressive Alfa GTV that keeps popping up in my Instagram feed. It's a remarkable custom - the best I've ever seen. But it's been converted to an electric motor. I'm sure that's neat in its own way. But it's not an Alfa anymore. And so it's not for me. And the comments from the proletariat on that post largely agree with me.

That formula % may vary somewhat depending on the marque, but does not change the fact. The character of the car - handling, balance, sound, smoothness, exhaust note, power, refinement, torque, revability, weight, and so on - are directly relational to the powerplant.

You may indeed have a very nice Jag with a V8 in it, with its own merits. But my preference would be a Jag V8 if you had to do a swap at all. Not a transplant from another brand. A Corvette with Ford engine is a ******* that no one wants. A Mopar with any engine other than Mopar = wrong. A 350 in a Range Rover Classic - that's fine in my book. Essentially it's a truck motor doing truck things. The Rover V8 was originally a Buick design anyway. Trucks are different so let's not go there. But a 350 in a 911 = wrong. A 350 in a Ferrari = wrong. An AC Cobra with a Ford engine = yes! An AC Cobra with a 350 = why? An Alfa with an electric motor = no thanks. A 350 in a Jag = meh. It's not a hard and fast rule, but you get my point.

 

Apologies for culling your remarks down to just two lines. But they're the most salient.

This debate has raged on since....forever. It's entirely subjective.Your own analysis is subjective even though you assert "fact" and end your remarks with the word "Period".

There are a millions ways to enjoy the car hobby. May it ever be thus. Let's embrace it rather than fight it !

Cheers
DD

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