Specifically, can these engines withstand reasonably high loads for extend periods of time ( Not high RPM ) without overheating ?

I have a nice 77 Chevy pickup that needs an engine and replacing the 350 is too easy. I've collected enough parts to install a 4BT Cummins but am now resisting due to noise. A 6.0 LS motor was a possibility but is too easy / boring.

The next step is a late Jaguar V12 simply because it will be an interesting swap with " what just went by? " exhaust note. My 80 Chevy 1 ton has a 292 in line 6 with good sound so I want to keep with that same format.

I'm resisting a Mercedes V12 mostly because I'm already doing the inline 6 Mercedes thing. Also the Jag uses a GM transmission so drive shaft flanges / shifter are a bolt on swap.

No in-depth knowledge though I've seen quite a few with high miles. Though in Europe due to high fuel costs they don't often get the use that say a diesel would - this means lower mile examples are easier to find.



They are famous for being hideously complicated and very expensive to fix. If, however, you are able to understand the systems and the complexities and are to approach the engine from a DIY I will adapt it point of view the engine itself is as basic as any other...


...I mean "what could possibly go wrong"


[cough cough COUGH]

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Hmm Mercedes v12tt would be sweet

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1993 e300
1995 e320
1994 e320
2006 s500 4matic
2004 Jeep wj overland
2001 Ducati 748
2004 Honda shadow aero

Yep, got it however I've done silly stuff before. The key will be to get a complete car, use all electrical for engine / trans and make this think it is still in the original car. The only real electrical adaptation beyond basic power is wheel speed signal.

Trying to piece meal an engine / FI system to an electronic trans / trans controller that it was not intended for is were electronic intensive projects become failures.

I could go with a 70's engine that uses a GM 400 trans making the swap a near bolt in ( use tail shaft from the truck into the Jag case ) and get the project done in a week however I'd be stuck with a 3 speed and ancient carb or FI.

I'd call this a much more complex and $$ swap. Plus the turbos will mute one of the project goals, the V12 sound.

My inline 6 truck has 2 36" glass packs inline on a 2 1/2 pipe, this makes for a pleasant non obnoxious sound.

Comforting words here =>

https://ralphhosier.wordpress.com/2011/10/02/de-mystifying-the-jaguar-v12/

If you haven't already got the engine and the plan is to use as much of the original systems as possible I'd be looking at the most recent versions

If you are used to American V8 spares prices I do think the costs of buying Jaguar bits will probably make your eyes water. I can't imagine for a minute it will be cheap especially if machining work is necessary.

There's a chap over on Landyzone who is playing about with a V12 in a series Land Rover - I can find the link if you want

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I know but of the v12s it’s the bees knees

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1993 e300
1995 e320
1994 e320
2006 s500 4matic
2004 Jeep wj overland
2001 Ducati 748
2004 Honda shadow aero

Load, hell yes. But cooling will need to be thought out carefully. An all-aluminum open deck motor isn't going to be tolerant of overheating. Cooling is your problem. A few fine points about cooling on these engines:

- this isn't really a 12, it's more like two sixes arranged on a common crank. The significance of this is that there are water exits in each head, each controlled by a separate thermostat. The killer on these motors is that the temperature sensor is on the right bank, which means that the thermostat on the left bank can be stuck closed and you will only notice a slight rise in temperature. Since you have a custom application, I strongly urge you to have two temperature gauges, one measuring output temperature on each bank.

- A consequence of the two-thermostat design is that the valve seats on the left bank tend to drop, that's what you need to be concerned with on a used motor.

- The primary native applications, XJ6 and XJS, had limited frontal area, descending hood lines and cramped space. This resulted in the most compromised radiator design in Jaguar's sad history of cooling system compromises. The radiators are small for the application, and they are a weird combination of two pass and one pass. ( The left bank flows from left to right in the upper rows, then joins the right bank flow, which then flows right to left in the lower rows).

-The radiators were also mounted lower than the motor, so there are bleed ports that probably won't be useful to you. But owners often overlook bleeding the radiators, so it's not unusual for them to be run with low coolant levels. Another result of the mounting is that the water exit is above the bottom of the radiator. It's just weird.

- Oddly, the radiators weren't redesigned over 20 years of production. As a result, the best radiator to use isn't the modern design, but the big radiator from the original V12 E-Type. (I can hook you up if you need help with this). Second choice would be the BeCool single pass XJS radiator.

- Kirby Palm's XJS help book has a lot of useful information on this motor. You can download it free here:

http://www.jag-lovers.org/xj-s/book/XJS_help.pdf

I have had the misfortune on working on a 12 cyl jag and had to replace the fan and the radiator and the thermostats - the later "stuck open failure" type thermostats are mandatory on them otherwise you can cook the engine.

You are right on the design though - it truly is a very poor execution of radiator design on the XJ. The engine itself delivers power almost like an electric motor - its very smooth.

Too bad jag couldnt take notes from mazda RX7 in making a cooling system for a furnace engine (rotaries run close to volcano hot)

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Learning a lot here folks, thanks for sharing the knowledge

The Jag v12 is an awesome engine with a fairly flat torque curve, and lots of torque. I had contemplated swaping one into a Jeep cj. Overall, if you address some minor design flaws and the coolong, they are very reljable engines, probably the most reliable production v12 ever made.. servicing is straight forward and easy if you have tge room, such as in your application, not so much stuffed in an XJ-S.

Other things to note, although all aluminum, the beast weighs in around 800 lbs. Also the earlier 75-82 engines are low compression 7.5 to 8.5:1, the HE engines 82-93? Are 10.5:1 compression but do run on 89 octane and are stout as well as easier to find stateside. The later 6.0 liter engines are also quite good. The transmission is a GM400 in the earlier HE cars, and GM 460le? In the 6.0 l cars. Both transmissions use a Jag specific case, so an off the shelf GM pattern box will not work. Chad Bolles, a reference in Kirby Palms book, does make and sell a jag to gm adapter that will allow tranny swaps to gm boxes. Also the Driven Man sells Tremec TKO 5-speed conversion kits, you could possibly source the bellhousing and tranny from him.
Fun project, but it is a project, if you have troubles sourcing an adapter, I have one of Chads originals, PM me, and I can see if I can dig it up

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

Thanks for all the great info everyone. If this project goes forward ( half the fun is research ) , I'd be getting a complete new as possible car so I have everything.

An auto 4 speed is a must, the 3 speed 400 does not have a deep enough 1st gear and by the time you use a deep rear axle to get any sort of pulling power, highway engine RPM is too high. At some point the truck would see towing a 20 ft box trailer so having an assortment of ratios is a must.

Late V12 used the 4L80E , which is more or less the 4 speed version of the GM 400. This gives me a choice of swapping tail shafts to match the truck. If this was using a ZF or other odd trans, I probably would not consider the swap.

As a side note, there is a turbo / supercharged later Jag that uses a MB 722.6 , this could be an interesting swap into a MB. Having at least something mechanical that bolts right up helps the project a lot.

The British transmission industry was well and truly dead by the time the XK8 came along. I believe all V8 Jags use 722.x transmissions. If you're looking for a powerful, modern engine, a supercharged AJ8 from an XKRS would be an interesting choice for 400+ HP. Be aware that the cylinder liners are not repairable, and there were timing chain tensioner issues on early engines.

Only the supercharged V8 jags had the 722.6 , NA V8's had some other trans. I know this from looking at where used parts lists and for a brief time was looking for a supercharged V8 with trans problems knowing it would be an easy fix.

I currently own 2 6l Jaguars. Nice engines but for a truck, I would suggest the LS swap.

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With best regards

Al