Originally Posted by Greg in France

All quite true about the heater. Also VERY true about electric fans from Grant. There is one point though:

As standard on the XJS, turning on the heater turns on the aircon, so that gives the engine more work to do in traffic. However, turning off the heater turns off the aircon AND turns off the auxiliary fan until the temp rises quite a bit. If you have the mechanical fan (which does practically zero at tickover) the engine gets quite hot - aircon off - before the auxiliary fan activates.

So FWIW, my best solution is:
Like Grant says, do the twin large electric fans mod. But also wire them to be switchable on manually regardless of heater settings, as well as one working automatically whenever the aircon is on, and the other big fan being normally thermostat controlled.

If you have the mechanical fan, a decent solution as long as the mechanical viscous hub is 100%, is to change the OEM fan (very old inefficient type) for the largest and most powerful you can find that will fit the shroud hole. THEN while keeping the OEm wiring, also wire it with a cabin operated manual switch. At the same time, fit an "off switch" to the aircon compressor earth wire, also cabin activated, so if you select "heat" from the system, it WILL function and heat the heater matrix but NOT cool the evaporator.

Then, in a hot coolant scare, this last mode enables you to turn off the aircon but turn ON the aux fan, AND keep the heater going! Then you get (a) extra cooling, (b) no extra engine load and (c) the extra heater matrix radiator cooling!

By the by, under these last circumstances, you should select DEFROST, which calls for MAX heating and over-rides any temp selected.

Greg

Originally Posted by Grant Francis

Nah, never been to your bit of dirt.

I conceded the temps there are different to here by a long stretch.

The Summer here is usually 5 months of 35c and above, with NO let up. In that time about 15 days are above 42c, so we are a boozy mob at best.

Mind you, I am in Sth Aust, "the driest state on the driest contiment", other parts of OZ are different.

Mine has the RH fan thermo wired, and a safety ON inside the cabin that simply switches that fans relay earth terminal. The LH fan is A/C only.

With the A/C on, the LH fan runs constantly, and I have NEVER had the RH fan come on whilst the A/C is ON. The fans are that good.

I also run 82c thermostats, and they are NOT Jaguar stats, they are Ford stats, as the Jaguar units at the time were too short, and did not shut off the by-pass ports, and the engine would/could run hotter than I wanted. This I have written about at length many times, and is freely available on request to your email address.

Originally Posted by plums

Another yes vote here. It's an old trick.

If your hood is hinged at the front, popping the hood open to the first
safety catch can also help.

Originally Posted by paulyling

That scares me Plums. I was driving in traffic when i first got mine and the hood flipped up and i had to stop in the middle of the road in traffic to close it ha ha ha. Funny now but was crapping myself at the time lol!

Originally Posted by JagCad

Yup.


I second or whatever the number as to Plum's comment. Trouble is the heat issue is liklely on a hot day. Not very comfortable to add a good blast of hot air to the cabin.
Time to drop the top and/or open all windows!!


Front hinged hoods/bonnets do help. No risk at all of a "blow up". jaguars as well as most cars suffer from a limited means of exhausting hot air from the engine bay.


Older USA critters had louvrers in one place or another to do this.


If one can, pull over and douse the radiator with water.


Caveat. Some pull over in a n overheat and shut the engine down Counter productive!!! No air flow and no water pump[ action not to mention no fan.
But if it's bad and you gotta, p[op the hood!!!!


Caveat II: Never open the radiator cap when the engine is hot. No positives, all negatives.


As I grew up in a desert, I learned a lot as to hot cars. both meanings actually.


Later, I lived and worked in CA's Imperial valley 125 F, from time to time. One Friday afternoon, my wife called me at my office. Great distress, the house AC quit. She and the kids "cooking". Rushed home. No service man available!!! 57 Chevrolet company car marginal cooling at those numbers. But, it had AC!!! Stopped at the ice house and put a block of ice in the handy space in front of the radiator and AC condenser. Wife and kids in car and off to the coast, San Diego. spent the week end there and returned to find the temps somewhat tolerable and an AC guy available.




PS: Even popping a rear hinged hood/bonnet to the safety latch is Ok, if road speed is kept down.


Lots more to share on dealing with high car temps in a hot climate.


Carl

Originally Posted by orangeblossom

So I will start off with a manual on/off switch for the electric fan and also the same for the Aircon Compressor, as I've noticed when the heater is on, you can almost feel the Compressor Working.

Originally Posted by orangeblossom

Do you mean actually drive along with the Hood/Bonnet open (to the first safety catch)?

Originally Posted by Greg in France

Indeed you can feel the aircon when asking for heat. The system works as two initially unconnected parts: the aircon part tries to maintain the aircon evaporator matrix at X degrees C (maybe about 4°C). It will do this regardless of what the cabin temp selected is.

Second the heater part pushes hot water through the heater matrix, also all the time, (except for when really cold cabin temps are called for when the system switches off the water tap on the engine bulkhead to ease the load on the cabin aircon - but for the purposes of this discussion ignore this wrinkle).

Putting these two aspects together are the air blend flaps: the entire system works by blending cold air from the evaporator with hot air from the heater rad to give you the selected cabin temperature.

So, when the heater is on, the aircon will be maintaining the evaporator at (say) 4°C regardless of whether you actually need cold air or not to achieve the selected cabin temp. For example in sub-zero mid-winter (unheard of in South Australia !) with the heater going full blast, the aircon matrix will still be being kept cold by the compressor!

FYI, OB The Great Palm's book has a bit about how to make the compressor cabin-switchable independently of the heater system. As for wiring the aux fan to be cabin switchable, be careful as you can inadvertently 'back feed' other systems (eg trigger the compressor). But loads of people here can help you with that.

Greg

Originally Posted by Greg in France

I am sure that he does, and it works. BUT, big but, there is an area of lower pressure above the bonnet when rolling and the bonnet is sucked up pretty hard against that catch! The catch itself is OK but the bit it clicks onto on the actual car body is held on by two pretty flimsy pop rivets. I changed these for small bolts and if you plan to open the bonnet at anything above walking pace, I recommend you do it too!

TWR when they raced the XJS (according to Allan Scott's fantastically interesting book) raced with the bonnet popped (or somehow made it so it would "accidentally" pop a bit) and the suction actually broke one of the fixings they had rigged up to allow the bonnet to open only so far !

Greg

Originally Posted by PhantomsPhorever

Long ago, I used to do this with my Jensen Healey in south Florida when stuck in traffic. Certainly helped then.

Mark

Originally Posted by Bc xj

Of coarse it would help. One of the first things our shop teacher told us. Ive done it on a hot hot day. Its not very comfortable but it works.

Originally Posted by baxtor

slight difference but very similar, I drove series I xj12 for many years and the bonnet WILL lift open at speed even though it looks as though it can't possibly do that. Once that happens it is very difficult to see where you are going.

Originally Posted by orangeblossom

Do you mean actually drive along with the Hood/Bonnet open (to the first safety catch)?

Originally Posted by Greg in France

TWR when they raced the XJS (according to Allan Scott's fantastically interesting book) raced with the bonnet popped (or somehow made it so it would "accidentally" pop a bit) and the suction actually broke one of the fixings they had rigged up to allow the bonnet to open only so far !

Greg