Jaguar V12 Cooling Issues

In a recent club magazine, there was a rather disturbing, ill informed article concerning over heating issues with a V12.    I feel this misleading information needs correcting.

We may all run classic vehicles but that doesn’t mean we have to remain with classic thinking or out dated technology.    Makes no difference if you run an XK engine or a modern V8 or V6, they all need proper servicing with the correct coolant to stop corrosion and transfer heat out of the engine to the atmosphere.

We will deal with the V12 as this was the basis for the gentleman’s comments but the same applies to any engine whether it be cast iron with an iron head, cast iron with an alloy head or totally alloy as most modern engines are. To run an expensive and massive engine such as the Jaguar V12 without the proper coolant is tantamount to driving a time bomb and will eventually wreck the engine beyond salvage.

The ‘gentleman’ experienced ‘furring’ of a six year old radiator core (these are a ‘cross-flow’ design in alloy with either metal or plastic side tanks) because he has most likely used plain ethylene glycol with ordinary tap water which in most parts of Australia is a definite NO,NO!! Tap water in this country in most regions is extremely hard containing a lot of calcium, mineral salts and other chemicals and minerals that are detrimental to the cooling system and the coolant within.

You should never use just Ethylene Glycol by itself as it will, as the gentleman has pointed out, become destructive as it heats up and changes it’s molecular structure to form acids. Always mix coolant concentrate with ‘de-mineralised’ or ‘de-ionised’ water (basically, distilled water). Tou wouldn’t mix your 20 year old malt whiskey with tap water now would you? Well, the same applies to top quality coolant!

All vehicles will get the maximum benefit by using modern up to date coolants which have a complete chemical package to virtually stop cooling system corrosion in it’s tracks IF the manufacturers instructions are followed to the letter! They also provide protection for rubber seals and glands within the system.

There is no point using new coolant if the cooling system is dirty; this is defeating the purpose. The complete system, including the heater matrix must be ‘reverse flushed’ which is flushing against the normal coolant flow, preferably using a combination of water and air which ‘turbulates’ and shifts any sediments lurking in various places. Just opening a tap or plug and letting it drain under gravity, does not remove damaging sediment deposits or pockets of old coolant trapped within.    If an engine block has been poorly maintained, you will need to remove core plugs and scratch around with a bent wire to dislodge hard deposits.    Same applies to radiators which need their tanks unsoldered to scour the matrix, or preferably replaced with a new core.

Professional engine builders will usually strip bare a block and have it acid dipped to completely remove scale and hard deposits which form an internal ‘insulation’ as it were, preventing efficient heat transfer which is the point of the exercise in the first place.   The block and radiator should always be flushed separately to prevent cross contamination.

It is preferable but not always essential to use a cooling system flushing agent before draining as this helps to remove scale, sludge and sediment build up before flushing.   It is most important to do this before changing to a modern coolant concentrate to maximise the full benefits of modern technology.
NEVER EVER mix coolant types!!

It’s no point in just looking at a thermostat, they need to be either tested for their proper operating temperature sequence, or preferably replaced as a normal service item, Ideally at the same time the coolant is changed.   They’re cheap enough, so why take the risk with such an expensive engine?
All Jaguar engines prior to mid year 1998 should use a green or yellow coloured coolant which meets the following specifications:    JAGUAR SPEC: Part No. JLM20404-3     FORD:   ESD-M97B49A

I make no bones about using and promoting NULON products as they are  Australian owned and manufactured and are amongst the best in the world to serve our precious vehicles: see I personally recommend using their “Long-Life Concentrate” which is green in colour and meets and exceeds the above specs.
For engines after Sept. 1998, you should use the RED Long-life Concentrate which meets and exceeds the following specs: NULON: RED Longlife Coolant Concentrate:    AS/NZS 2108.1:2004 Type A UPRATED JAGUAR-FORD SPECIFICATION: WSS-M97B44-D

It is not recommended to use a pre-mixed coolant as these do not offer enough protection.     Most are only 33% mix, whereas Jaguars need 50% mix to be truly effective, that’s why concentrate is the best course of action, meaning 1 litre of distilled water to one litre of coolant concentrate, mixed in a jug before administering to the system.
I have had some people complain to me that their system leaks after changing coolants, this is no fault of the coolant but a mechanical fault in the cooling system caused by old age, poor maintenance and using the incorrect additive. That’s why it pays to make sure you have a mechanically fit cooling system before you start.

There are no short cuts here!! Get it pressure tested, replace all cooling hoses that are below par and replace all those horrible factory fitted spring clamps with proper stainless worm drive clamps; not the cheap Asian slotted type either, the proper ‘Jubilee’ type of clamp. I ran a 1982 Rover 3500SE which has an all alloy V8 for 20 years and 386,000klm using the correct coolant mix and the inside of that engine was clean enough to eat off!    It still ran it’s original radiator and water pump because I religiously flushed and changed the coolant every two years, despite what manufacturers state!   My present 1998 XJ8 4.0 litre Sovereign has covered 176,000klm and the cooling system is perfectly clean because it has been maintained properly by the original owner and myself.

The Jaguar V12 is no different to any other cooling system but because of the prodigious amounts of engine heat and the minimal cooling system, it needs every advantage it can get if it is to survive our Australian summers and heavy city work. Make sure all your fans, whether they be engine mounted with a viscous drive, or electric (as on the later versions) and some will be fitted with both!

The V12 as other engines will need to be ‘bled’ properly to eradicate any air trapped in the system as this can be very damaging to components by turbulating the air trapped within the system to act like a form of abrasive.    There are usually bleed screws available for this purpose; check your appropriate manuals for the variations on any engine. Usual procedure is to undo bleed screw with engine running to allow any trapped air to escape and close bleed screw when coolant begins to dribble.
One of the biggest killers of V12’s is leaking cylinder head gaskets which were basically eradicated on later HE and six litre versions.    When replacing thermostats, don’t forget the all important pressure caps; replace the lot!

Another important additive that is used a lot in the racing game is a ‘wetting agent’.     These can be obtained from various manufacturers and actually make the coolant do its job better.

With the cramped engine bay of any V12, there is a lot of under bonnet heat which is hard to get rid of and a very successful product produced by another great Australian company, Davies Craig is their electric coolant pumps which are fitted ‘in line’ to the cooling system.   These electric pumps can be manually switched, or thermostatically controlled and work wonders on a big engine like the V12.
As you will know, an engine driven cooling pump is governed by engine revs and when you need to pump the coolant around the quickest, the pump is running at it’s slowest at idle in a long line of traffic!    Later series V12’s were fitted with an electric fan to augment the engine driven fan but it is still border line.   KEEP ‘EM COOL!

** Please read the very comprehensive fact sheet produced by NULON along with this article.      Make sure you read it as there are a number of enlightening facts concerning cooling systems **
Cheers, Maximus