Jaguar XJ-S. Manual - part 46

 
 

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FILLING THE COOLANT SYSTEM:  The ROM and the Haynes both provide a detailed coolant fill procedure and 
give dire warnings about engine damage caused by hot spots if the procedure is not followed.  Allow me to add: they 
ain’t kidding.  Reportedly, one indication that the system has not been properly filled and bled is that the coolant level 
light comes on every now and then while driving.  Another is a temp gauge that seems to wander around. 

Of course, you could just take your car to the Jag dealer and let the experts change the coolant so you don’t have to 
worry about it, right?  Get real.  Stefan Schulz:  “In my experience (in the bad old days, that is, when I still let garage 
mechanics near my car), they never seemed to follow this procedure because the coolant level light would behave as 
you describe after they messed with the cooling system.  When I started doing my own maintenance and followed the 
procedure to the letter except for the leak sealer I never got the low coolant light on when the engine was running.” 

Steve Gallant:  “Same for me here.  My car was serviced by a very reputable main dealer as part of a pre-purchase 
service.  After receiving the car, I noticed the low coolant light came on on my first drive.  I performed the factory 
procedure for filling/bleeding, and the light was extinguished.  I must have added close to a quart of coolant.  So even 
dealers don't take the necessary time to perform this operation 100% successfully.” 

Wally Magathan:  “My car was also serviced by a reputable dealer, but I didn't know it was routine for them to ignore 
the bleed procedure until now.  I've now bled the system, put in almost a gallon, and hate to think what's been going on 
in the engine in the month since they "fixed" my radiator hose.” 

Jim Isbell provides a great tip on filling the coolant system:  “Getting the water into the system has always been a 
problem on the XJS because of the two fill points.  I always tried to do it on level ground before and spent many 
minutes shaking the car to get all the air out of the system.  Today, just by accident, I was parked in the driveway with 
the nose of the car elevated and I didn't feel like moving it.  So I pulled the cap on the header tank and filled the car 
(about two quarts) then I pulled the cap on the crossover pipe and added another quart.  The air bubbled out quickly and 
the car was completely full in no time.  I recapped both vents and it's finished.  From now on I will park the car with the 
nose uphill when I fill the radiator.” 

The engine is deliberately designed for the coolant to flow upward with no air pockets, but when parked on level 
ground it just barely flows upward.  Tilting the nose up should make the air clear out a lot better.  Offhand, it’s probable 
that you can’t have the nose too far up until the air bleed port on the top left of the radiator is higher than the fill 
opening on the crossover pipe. 

Be sure to bleed the air out of the heater circuit while filling the cooling system.  See below. 

 

AIR BLEED VALVE:  At the top left corner of the radiator is a small fitting used to allow air out while filling.  Mike 
Morrin says, “The first few XJ-S (1975 model year) left the factory with a threaded plug.”  Then they switched to a 
little winged valve for most pre-H.E. cars -- but for H.E.’s, they went back to the plug.  Morrin:  “The owner’s 
handbook and manual give instructions for both types of fitting.”  Both items were the same thread, 1/8” BSPP -- so if 
you’re here in the US, don’t lose that plug!  If you’d prefer the convenience of the valve, C45587, it will fit where the 
plug fits; the valve sits a little higher and therefore closer to the hood, but this doesn’t seem to be a problem. 

 

AIR BLEED AT THE HEATER VALVE:  There is none, but there should be.  Since the line comes out of the right 
side coolant manifold, goes upward until it gets to the heater valve and then downward until it connects to the bottom 
left corner of the radiator, it forms a big bubble when filling the coolant system.  Therefore, you need to disconnect a 
hose at the heater valve to let the air out when filling.  A disconnected hose creates two openings, one on the end of the 
hose and the other on the end of the fitting it was attached to.  As you fill, coolant will start to pour out of one of the 
openings first; put a thumb over that opening and continue to fill until coolant starts to pour out of the other opening, 
then reconnect the hose.  

Of course, it’d be more convenient if there were actually a bleed port.  Douglas Dahl says, “2 clamps and a $0.99 5/8" 
connector at any auto parts store.  It is the same as the T's used in the flushing kits out there and comes with a screw 
top.”  These black plastic “flushing tees” are commonly available in 1/2”, 5/8”, and 3/4” size, and you’ll need the 5/8” 
for this job.  The straight section of the tee has hose barbs of the specified size while the connection off the side is a 

 
 

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male garden hose fitting, and it comes with a blank-off cap with a rubber washer inside.  It really could not be any 
simpler to install or use.  If your local auto parts store doesn’t sell these flushing tees individually, it may sell the 
flushing kits which contain three tees -- one of each size -- plus one cap and a few other items, all for less than five 
bucks so it still won’t break you.  Note: you might want to check the passages inside the tee for plastic mold flashing 
before installing. 

Please note that installation and use of an air bleed in the heater circuit does not mean you don’t need to follow the 
prescribed procedure for filling and bleeding the cooling system.  You will still get air in the system when filling; we 
just hope that you will trap less air in the system by bleeding air from the heater circuit. 

When filling the cooling system, it is suggested that you run the car for a few minutes with the climate control system 
off.  With it off, the heater valve will remain open, so the cooling system will have a chance to push the air pockets out 
of the heater circuit.  With the system on, it may just close that heater valve as soon as the engine is started unless it’s 
cold enough inside the car for the system to call for heat. 

 

ANTIFREEZE:  Don’t operate the Jag or any car without antifreeze in the cooling system.  The name “antifreeze” is an 
unfortunate misnomer, and pure water is a totally unacceptable coolant -- even in Hawaii.  Antifreeze not only prevents 
freezing, it also retards corrosion and crud buildup, helps prevent boilover, and serves as a water pump seal conditioner. 
 Running pure water will result in early water pump seal failure.  Also, replace the antifreeze annually, because the 
inhibitors in it wear out and it becomes corrosive. 

Scott Fisher sends the following wisdom:  “In the context of the automotive cooling system ethylene glycol is not an 
anti-corrosive agent; it is in fact corrosive.  To offset this fact, manufacturers add anti-corrosives (inhibitors) to the 
glycol.  These preparations, while in good condition, perform well in both minimizing corrosion and preventing 
freezing of the coolant.  However, over the life of the coolant the anti-corrosion properties of the inhibitors are depleted. 

“Water aids corrosion in three main ways:  1) bringing free oxygen in close contact with the metals so that corrosion 
(oxidation) can occur.  2) Water is conductive.  Once water has been flowing in your cooling system for some time, its 
conductivity will rise as it picks up metal ions.  The water may serve to promote electrical activity which may erode 
metals by galvanic action.  3) Some of the metal ions in the water may also react directly with the metal surfaces. 

“Apart from supporting the above three processes, ethylene glycol has the added unfortunate property that it oxidizes 
through several stages to oxalic acid.  The products of ethylene glycol oxidation by oxygen and subsequent reactions 
include: aldehydes, carboxylic acid, nitric acid, glycolic acid, glyoxylic acid, oxalic acid, formaldehyde and formic acid. 
 Most of the series of oxidation products to and including oxalic acid are directly corrosive to metals.  Added to this, 
oxalic acid is highly toxic. 

“To combat the above acids and other corrosion activity, antioxidants and alkaline formulations are added to the glycol 
mix.  These include many compounds which are used in cooling systems where antifreeze properties are not required 
and include primary, secondary and tertiary amines; organic and inorganic phosphates, silicates cresols and other 
phenolic substances; a wide variety of sulfur compounds; soaps; alkali metal salts; and borates. 

“These inhibitors slow down the corrosion process caused by the glycol and the water.  They may coat the metal 
surfaces and prevent corrosion by passivation.  Passivation is the process where the a protective film forms on the metal 
which prevents further contact with the solution.  Unfortunately, in all coolant preparations (with or without glycol) the 
inhibitor system (during engine operation) is being continuously depleted in the performance of these actions.  For this 
reason, proper cooling system maintenance is critical. 

“One aspect of cooling system maintenance that we can all easily follow is to minimize “aeration” of your coolant.  
Aerating accelerates the uptake of free oxygen from the atmosphere.  As free oxygen is one of the essential ingredients 
for corrosion, the importance of minimizing it’s uptake is clear.  To this end you should make sure all your hoses are in 
good condition and clamped tightly.  “Closed systems”, where an expansion tank and recovery system closed to the 
atmosphere is used, also help in this regard. 

“If you overheat (boil) glycol-based coolants they must be replaced immediately as this accelerates the oxidization 
process of the glycol to acids.” 

 
 

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LONG LIFE COOLANT:  Peter Cohen says, “I noticed that the manual called out “phosphate free” coolant.  The 
statement I am referring to is on Page 26-03 of Volume 2 of the XJS Service Manual (JJM 10 04 06) under the heading 
“ANTIFREEZE”.  The V12 HE motor is essentially unchanged since long before the existence of non-phosphate 
coolant.  Ergo, the Jaguar V12 has been doing fine on normal coolant for all these years, so why ask for non-phosphate 
now?” 

“After much searching, the only non-phosphate stuff I could find at the time was Prestone 460 Long Life coolant.  The 
Prestone 460 has the distinct disadvantage of being brown, so now coolant leaks are the same color as oil leaks (and the 
same color as rusty old coolant).  I have since found Texaco Havoline Long Life, which is orange.” 

Jim Belkoff answers, “Beyond the phosphate-free issue and the long-life issue, Texaco DEX-COOL (and I assume the 
Prestone equivalent) contains no silicates.  From what I understand, silicates are abrasive and gradually eat away at 
water pump seals.  Texaco and GM have done tests to prove this new coolant results in fewer water pump 
replacements. 

“The reason the new coolant lasts so long is the carboxylate inhibitor system that’s added to the base ethylene glycol.  I 
would suggest taking a look at Texaco’s website (

www.texaco.com

). 

How important is phosphate-free coolant?  Apparently we should ask the folks at Saturn.  Cohen:  “In their first year of 
production, Saturn recalled and destroyed all of the first cars they sold because "they were shipped with the wrong 
coolant, which could destroy the engine block".  Given that they could simply have issued new motors, this was an 
impressive waste of money.” 

Peter Cohen says, “DEX-COOL apparently eats silicone sealants.  If you are replacing your water pump, do not use 
silicone sealant on the gasket.  Either use no additional sealant, or use Permatex.” 

 

LONG LIFE COOLANT -- MAYBE NOT:  That orange long life coolant sure sounds good, but eventually enough 
negative reports appeared to convince many owners to stick with the traditional green stuff.  In fact, enough negative 
reports appeared to convince many auto mechanics to avoid the orange stuff like the plague.  Gary Penovich says, 
“Chevrolets and other late model GM cars have been affected by brown sludge.  It seems that extreme driving 
conditions and/or low coolant situations lead to a gelatin-like thickening of the stuff.” 

From the 

http://www.imcool.com

 site comes a report about a presentation made at the MACS 2001 Convention and 

Trade Show in Orlando, Florida.  Remember, the presentation was made by GM and Texaco reps -- but that doesn’t 
mean the info provided isn’t useful.  The report is too lengthy to include in entirety here, but a few points can be 
summed up: 

ƒ  They’re giving radiator caps the lion’s share of the blame.  “Drop-center, vented radiator pressure cap.  GM found 

this cap to be less helpful than a spring-center cap in controlling the formation of contaminants in the cooling 
system.  If contamination forms, the debris fouls the valve and restricts its ability to seal.  In turn, the coolant boils 
at a lower temperature.  Coolant loss is accelerated and so is the accumulation of contaminants.  You must replace 
all suspect radiator caps, especially those with a Drop-Center design, with a Stant Model 10230 or 11230 (Spring-
Center type).” 

ƒ  There is a 14-minute GM training video available that is considered a “must see” for techs working on late model 

GM cars.  The title is “Understanding Radiator Cap and Cooling System Contamination”, part number 
RADCAPK.  GM and Texaco are claiming “The coolant problems found in this survey were caused by system 
contamination, and not due to the breakdown of DEX-COOL.” 

ƒ  Keep the cooling system filled.  In fact, fill the reservoir bottle to “Hot” level when the system is cold. 

ƒ  Always make sure the antifreeze/water mix is at least 50/50. 

ƒ  “In...applications where the radiator cap is mounted at an angle to the ground, the vehicle is more susceptible to 

radiator cap contamination and its related problems.  The Stant 10230 is a wise choice for these vehicles.” 

 
 

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Wally Plumley, on the Porsche 928 discussion list, discussed coolants with Texaco reps and learned that long life 
coolants are not suitable for “open” cooling systems in which air is present in the cooling system.  In other words, it’s 
not suitable for systems that don’t have a coolant overflow tank -- such as the pre-H.E. XJ-S.  It’s also not suitable for 
systems that leak.  “Silicates in conventional coolants will "plate out" or coat metal surfaces inside the cooling system.  
If the cooling system gets low on coolant, the plated silicates will give some corrosion protection to the metal that is 
then exposed to hot, moisture-saturated air.  DEX-COOL has no silicates, so if the coolant level gets low, the metal 
exposed to hot, moisture-saturated air has no corrosion protection, and will corrode relatively quickly.”  Of course, this 
wouldn’t matter to anyone whose car never got low on coolant. 

Bernard Embden argues that DEX-COOL is not only inappropriate for systems that don’t have an overflow tank, but 
for system with unpressurized overflow tanks -- which would include all Jaguar XJ-S’s.  “On my 88 Grand Prix with 
its non-pressurized expansion tank, (tank does not have a "pressurized radiator cap") a nasty sludge built up around the 
expansion tank filler cap with DEX-COOL installed.  The crap was hard and not easily removed.  Based on my 
experience, it appears that DEX-COOL reacts with the atmosphere to form this sludge.  GM agrees that low coolant 
resulting in radiator contamination is the death bell of DEX-COOL.  A "low coolant" condition creates an "air pocket" 
within the radiator that allows a deposit accumulation unique to DEX-COOL.  Once this deposit attaches itself to the 
radiator cap, the cap loses its sealing ability and a vicious cycle of low coolant/more deposits starts. 

“Without a pressurized radiator cap, the cooling system has a large and variable "air pocket" in the non-pressurized 
expansion tank.  This allows DEX-COOL deposits to start to build up immediately in the expansion tank and is 
ultimately drawn to the radiator cap.  Once on the radiator cap sealing surface it prevents proper sealing.  From this 
point on your radiator is on borrowed time.” 

 

LONG LIFE COOLANT -- MIXING WITH CONVENTIONAL COOLANT:  Jim Belkoff quotes the DEX-COOL 
literature as claiming the stuff “is compatible with regular coolant, but the long-life properties are somewhat negated.” 

Well, maybe not.  Brian Vaughn found this report at 

http://www.imcool.com

:  “"As a laboratory compatibility test, we 

intentionally mixed DEX-COOL with a conventional coolant and subjected the mixture to a sample of fresh aluminum. 
 The resulting data suggests that aluminum corrodes at an accelerated rate when subjected to this mix compared to pure 
DEX-COOL or pure conventional coolant.  As a result, Amalgatech recommends that the coolants not be mixed."  The 
commentator is Ed Eaton, Chief Engineer of Amalgamated Laboratories, Phoenix.” 

Texaco reportedly disputes such findings.  At the presentation made at the MACS 2001 Convention and Trade Show 
(mentioned above), GM and Texaco reps said:  “Mixing a “green” coolant with DEX-COOL reduces the batch’s 
change interval to 2 years or 30,000 miles, but will otherwise cause no damage to the engine.  In order to change back 
to DEX-COOL however, the cooling system must first be thoroughly drained and flushed.” 

 

RETROFITTING OLDER CARS WITH LONG LIFE COOLANT:  Jim Crider says, “A few years ago, someone 
thought a long-life coolant (original plan: life of vehicle) would be a Good Thing.  This leads to Organic Acid 
Technology coolant (OAT), which is marketed as "DEX-COOL" by GM and has been factory-fill in their products 
(except C4 Corvette -- not sure about C5 Corvette) since 1995.  It's the orange or orangy-red stuff.  Someone along the 
line decided the word "acid" was a Bad Thing to try to sell, so OAT was recursively changed to Organic Additive 
Technology.  It can go 5 years/100K or 150K miles -- provided it's not mixed with other coolant.  OAT has less 
cavitation resistance than silicate-based coolant, and can attack certain sealing materials, so it's not a good idea to 
convert a green-coolant car over to OAT unless the manufacturer says it's okay.  OAT also has a tendency to stain 
translucent plastics in things like overflow bottles and pressurized de-gas bottles with a funky brown crud.  Oh, and 
OAT from one manufacturer isn't necessarily compatible with OAT from a different manufacturer.  Texaco is GM's 
OEM supplier and is licensed to use GM's "DEX-COOL" trademark on their aftermarket packaging. 

“Many European automakers use a hybrid of OAT -- HOAT (Hybrid Organic Additive Technology -- clever, huh?), 
which is the OAT package with a small amount of silicates added to increase the cavitation resistance and make it less 
aggressive against those seals and gaskets.  This is often pale yellow in color.  DaimlerChrysler is using it in several car