Overheating

[Martec]

Just to add my pence worth, I'm with Alec on this one. It all comes down to what the cooling system was designed to do and what parts of the cooling system are not doing their job now.

The rapid burning of fuel in the cylinders creates heat energy, unfortunately a petrol engine is only about 35% efficient in turning this into rotating energy and so the rest is washed away by the coolant.

The thermostats job it to try and maintain a temperature decided upon my the engine manufacturer, in our case about 70 degrees C, but its other job is to redirect the water flow as the engine warms up and to try to ensure coolant circulates around all the cylinders particularly the rear ones, more difficult to direct cooling to.

The pump.......it circulates the coolant.

The radiator when clean (new) allows the air to cool the coolant.

The front of the MkII is not good for directing air in the grill and through the radiator, hence it is essential to keep the rather large engine driven fan (I fitted one from a BMW but later found out the steel Jaguar one is quite good)

The radiator in practice is marginal, so by raising the pressure to 4 psi rather than an open system it raises the temperature before which it will boil to give you a chance when heavily working the engine. Again in practice the pressure cap is dependant on the depth of the neck of the radiator (my early one is the deep neck one and so has a 4psi deep cap).

The correct type of thermostat is essential usually the sliding sleeve type for the older manifold and modern moving plate type for later engines and manifolds (I think 4.2 engines had them). I paid Annie Jenkins a fortune for an original thermostat to get mine on the road 13 years ago.

From experience I have not been able to sufficiently clear a clogged radiator by chemical flushing so had an uprated core put in.

As Oldtimer says the best level of antifreeze is just below 50/50 (from experiments of another member over 50% antifreeze the cooling effect of the coolant started to reduce, so now I try to get about 45% antifreeze. Again the reason you change 2 year bluecol in these engines or 5 years with modern engines is not because of loss of freezing protection but because the anti-corrosion package in the fluid is all used up and corrosion will start and clog the radiator. Aluminium, cast iron steel and copper, what a lovely corrosion cell. My local tip will take antifreeze to recondition it!!

The whole system need to be kept in good condition to work faultlessly. Just to turn the above on its head I found a strange occurrence a few years ago.

I wasn't happy about the loss of coolant from the radiator as I couldn't see what was left in the system, so I fitted an expansion tank from 'something' in the scrapyard and was amazed by the displacement of fluid between hot and cold. I had the pressure cap on the radiator and the expansion tank open to the atmosphere, all was well and it maintained 70 degrees, but when I fitted the pressure cap to the expansion tank and a simple cap to the radiator it quickly went up to 90 degrees. When cooled down I reversed the caps and it has remained at 70 degrees ever since???

My level of engineering knowledge doesn't explain that, so I stick with what works.

Best of luck
Brian

[PPV]

Just to let you know that my local garage removed the radiator and tried caustic solution but when they back flushed little came out but they felt it was restricted internally. They sent the radiator to their friendly specialist in Stoke who advised that in their view the flow was down approx 30% and recommended a re-core.
Rang around (incl SNG etc) and found they were competitive so agreed that the work go ahead.
Just got the car back and been for a long test drive and found the temp stays stable at about 75 to 80 on the gauge so very pleased. Only disappointment is that the original fitment drain tap fitting has not been used on the radiator.
Thanks to all for advice.
Regards,
Paul

[piman]

Hello PPV,

regarding your drain tap, it would sound as if it was not a re core as that entails refitting the top and bottom tanks which would have retained the drain tap.
It's worth trying them to see if they still have the old radiator and refitting that tap is just a five minute job for them?
I do think that it is a nice feature with it's remote lever to operate the tap.

Alec

[Martec]

Hi PPV,

Glad to hear your overheating problems are vastly improved.

I note that you say the temperature gauge is now reading 75-80, Last year I experienced my temperature gauge reading moving up and down a little, also the fuel gauge, I run on lpg and have never seen a Jaguar make fuel!

Both gauges are feed a supposedly stable 10volts from a mechanical voltage stabiliser, in practice the gauges are heavily damped (hence the slow rise on start up) and the mechanical stabiliser just cuts in and out with the alternator voltage.

I made up a few electronic voltage stabilisers (you can buy them online for about £10) and that gave a steady reading on both gauges. This resulted in a consistent reading of 70 (cooler conditions than at present) confirmed by a remote thermometer and an alcohol thermometer in the top of the radiator. Ken Jenkins later said that below 70 the engine will wear more.

Best wishes

Brian

[PPV]

Hi Alec, it was a recore but they used a new bottom bottom tank as they were concerned at the thickness of it once dismantled. I was more familiar with the top end and that is the same one as I recognise the one or two dents that were there before. I do have the drain tap and remote link which was returned to me though for future use.
Hi Brian thanks for your note. The temp variation is I think because it has no thermostat and just varies when it is running hard and then I slow down.The fuel gauge is rock steady so 'touch wood' I think the current voltage stabiliser is ok. I will keep note of your info though.
Regards,
Paul

[piman]

Hello Paul,

it's not advisable to run without a thermostat as it upsets the balance of water flow in the engine.


Alec

[Martec]

As per Alec's comment.

The XK engine is very long so the rear two cylinders are a long way back from the water inlet/outlet and if water doesn't circulate then the cylinder will overheat and pick up and possibly seize (probable scrap engine). The thermostat is essential to help direct water to that area.

Brian

[PPV]

Alec/Brian, thanks for advice re thermostat. I will try and find out which one I should have and fit it asap.
Regards,
Paul

[oldtimer]

And some Anti Freeze at 50/50 mix I hope

[PPV]

Yep, 50/50 antifreeze duly installed!