Hello to all,
Please forgive me if this has already been covered umpteen times, but my searches didn't find anything addressing my query.

I am considering fitting a coolant overflow bottle (or tank) as the original set up whereby (unless I've misunderstood things...) the only way to check the coolant level is to fill radiator which then results in the car dumping something like two litres of expensive coolant on the road as soon as you get it hot. I have purchased a suitable (long reach double seal 4 PSI) pressure cap and have been experimenting with an empty 5 litre container with the overflow tube going down to the bottom of the container. That's how I know that if brimmed the car dumps around 2 litres of coolant when you get it hot... This system is the same as fitted to Triumphs and Lotuses of the sixties - that's where I got the idea. The hot expanded coolant goes into the bottle, not onto the road, and then it gets sucked back in when the engine cools. The benefits are (a) no more loss of coolant, (b) you can see whether or not the coolant level is OK, and (I imagine) better initial cooling of the head on starting (as the top of the circuit contains coolant when cold, not 2 litres of air).

So here are my questions.
Is it normal that from cold fill to hot engine 2 litres of coolant is ejected?

Is there any reason (other than "originality") not to fit such a system, which seems to me to be very much better than the 50's design?

Does such a system already exist as a conversion? (NB I am not talking about a pressurised header tank - just a simple overflow bottle).

All thoughts and comments welcome (however rude) please!

Tony

 

It is most certainly not normal to dump two litres of coolant when the engine heats up. OK, coolant expands when heated, but not that much ! On Jaguars of this era, provided the coolant level when cold is correct, the radiator design is such as to provide sufficient expansion space. Later on, expansion tanks were fitted, but the radiators were then completely full of coolant with no air space at all.


There is obviously something wrong with the engine coolant circuit. If the thermostat is not working, the coolant in the engine could be boiling and forcing out coolant. Have you checked the thermostat, and also have you checked for head gasket failure ? What you are proposing is not a cure for the problem.

 

Thank you very much for your very helpful reply Fraser.

Obviously if I asked whether dumping 2 litres of coolant between brimmed cold and engine hot was "normal" it was because I do have a doubt about this.

I would very much like to know what is normal for an XK150, which clearly must dump some coolant each time it is brimmed full. And although I have a doubt, I do wonder whether it may in fact be normal, based on the following information.

I have no reason to believe that there is anything wrong with my car - the thermostat starts out closed and opens at the right temperature, the car does not overheat, the oil is normal, the oil filler cap clean, and the cylinder compressions are all both reasonably good and reasonably consistent. Equally important, when I initially started my expansion bottle experiment I purchased an expansion bottle destined for a Triumph TR6. This overflowed big time when the engine was hot. Its capacity is about one litre. The coolant capicity of a TR6 is 11 pints, including the expansion bottle. The coolant capacity of an XK150 is 23 pints, and that's without an expansion bottle. More than twice the volume of liquid to expand...
So can anybody tell me how much dumped coolant is normal for an XK150 that's had its radiator filled to the brim, please?
And a related question plaese. How on earth are you supposed to check the coolant level without at least bringing the coolant level up into the filler "neck"?
Many thanks

 

Radiators in these old cars are not filled to the brim. Like the older Fords, you fill until the tubes are covered and stop. My 3.4 is filled until tubes are covered and you feel fluid in the upper hose. Since you have a 2 litre overflow, put in 2 litre less and see what the temp does. ( carry extra fluid with you until you find the happy medium),

 

Many thanks for this info, Jagfixer.

It doesn't sound as if a 2 litre quantity of overflow surprises you, then?

In the case of the XK150 you can't really see the tubes due to the "neck" leading to the coolant filler cap. Perhaps with a little mirror - I'll look. I will certainly also try to see at what point I can feel fluid in the upper hose - presumably way before the coolant becomes visible at the bottom of the "neck" if there's meant to be 2 litres of air in there when the engine is cold. I probably won't get try the car again until Thursday now, though.

Reverting to the main point of my original post, is there any reason (other than its lack of originality) why fitting a 60's technology overflow bottle would not be an improvement to the 50's set-up?

 

#1. These old cars run with a cap pressure of 4 Lbs. #2. Not enough vacuum to pull fluid from overflow. #3. Finding proper cap that could be used for an overflow. #4. An increase in pressure could and will cause core plugs to blow and fluid seepage thru gaskets between the aluminum and iron components of the engine. Fill the radiator until you just see coolant on shelf inside cap opening. Been working with and owned these cars for 51 yrs., and the biggest problem is cooling, which is usually handled with bigger radiators and electric fans. If the 150 is not overheating, just back off on how much fluid you put in.

 

Hello Larry,
and thank you very much for taking the time to reply further.

I do have a suitable (long reach double seal 4 PSI) pressure cap and I was very careful to only get a 4 PSI one. I'm not sure, though, why the cap relief pressure being only 4 PSI would reduce the coolant circuit's ability to suck back in the expanded coolant? Could you explain that, please?

I will definitely keep to what you suggest regarding filling, thank you.

Thanks again

 

I would be under the assumption, that if the system was necessary the Jaguar engineers and race crews would have instituted them 60 years ago. Water and coolant mix is 8 lbs a gallon and a 4 psi system is almost like taking the old Ford Model A and running with no radiator cap. I am not an engineer, just wrenched on these cars since 1964 and I don't add any fans or bigger radiators to mine, as they are always up to snuff. Also, considering that no car in these years had an overflow. Cooling problems were usually lack of maintenance and the cars I get from the woods or garages are usually dropped from a small problem that is figured to be not worth the time or money. I just took apart a dash in a 62 MK 2 that I parted 35 yrs. ago and it's death was a short behind the dash at the ignition switch. Body and engine were good. Back to coolant, I am not going to argue, do as you want, as I don't have time look up the books and write a comprehensive essay on the physics of the Jaguar system that Sir Haynes developed and assemblied some 68 yrs. ago with the longest run of a single engine yet. 1948-1987 and some 4 million cars later.

 

There will be no harm done putting in an expansion tank and fully filling the radiator. My MG Midget of 1977 has such a tank, yet earlier cars don't. Maybe it had to be done due to the new use pattern of cars as they were able to drive on motorways and so on, and people unfamiliar with cars bought them and didn't expect to spend any time checking things over, like coolant and oil levels

 

INTERIM REPORT : SO FAR SO GOOD

I have been running my XK150 with a temporary two litre overflow bottle sited ahead of the radiator in the huge space between the radiator and the chrome grill. It is not an elegant location but it has served to show that the system DOES work. I would stress that my reason for attempting to fit an overflow bottle is not at all because I object to spending time checking things over, like coolant and oil levels. Rather it is because I really don't understand how on earth you are supposed to check the coolant level on an XK150 (with its long neck up to the filler cap that makes peering down onto the top of the coolant tubes impossible) without at least topping it up until some coolant is visible, which then gives rise to it's dumping the excess as soon as the engine is hot.

The benefits are (a) no more loss of coolant, (b) you can see whether or not the coolant level is OK, and (I imagine) better initial cooling of the head on starting (as the top of the circuit contains coolant when cold, not 2 litres of air).

All of which brings me back to one of my original questions - does such a system already exist as a conversion? (NB I am not talking about a pressurised header tank - just a simple overflow bottle like that fitted as standard to the likes of the TR6, but much bigger).

Tony

 

Hello all,
My atmospheric overflow bottle system still seems to be working perfectly and I commend it to you for all the improvement reasons that I have previously posted. I have also just come across this on the Jag-Lovers site - so I am not alone:-

Most new cars have "burp tanks" (a non pressurized reservoir) installed on their cooling systems. Old Jaguars like them too! Because the cooling system on the XK engine is large in volume, the tank capacity needs to be large as well. A half gallon would be minimum with a gallon being better. The reason burp tanks work so well is twofold: 1) You don't get air back into the cooling system (air doesn't cool anything) and 2) the oxygen from the air doesn't make hard water drop out as "boiler scale". The water jacket of the engine must be free of scale to transfer heat well. You will need a new radiator cap that allows the drain tube to draw water back from the burp tank. Then you'll need a canister of adequate volume with either a long tube that goes to the bottom of the canister or a bottom take-off on the canister itself. After filling the system with an appropriate antifreeze/anticorrosion material and water you should only need to top up the burp tank. When the engine is fairly hot the burp tank will be nearly full but as the engine cools, it sucks back the fluid keeping air out of the system. If it empties the reservoir when the engine is cold, then it's not big enough! On our race cars we've usually mounted the reservoir off in the left wing. A look under the bonnet shows nothing unusual other than the changed radiator cap and the longer overflow hose.

Tony

 

Using the XK150 model as an example for this discussion ... The (factory-stated) coolant capacity of the XK150 is 13 litres. Assume the car is at rest at 15C (60F) when the radiator is topped up to max. Assume the engine's coolant operating temperature rises from 15C to 90C (195F) as measured as the coolant exits the head past the temperature sensor bulb. Using a thermal coefficient of 210E-6/C (0.000210/C), then the increase in the coolant volume (assuming it is potable water) is not more than 205mL (a volume increase of 1.6%) if ALL of the coolant has an average temperature of 95C. The average temperature has to be less than 95C as the coolant is colder than 95C when it leaves the radiator bottom tank up towards the water pump. A further factor is the expansion of the entire engine and radiator as each heat up, and this engine and radiator expansion will reduce the volume of hot coolant being ejected past the 7psi radiator cap to atmosphere (or to an expansion tank if fitted).

Thus the theoretical expected loss of coolant when the radiator has been topped to max and then the car engine is run until it is fully hot, is about 200mL. Since this is a theoretical volume loss, the volume in reality might be greater. A possible (or even probable) reason for greater coolant loss is that the coolant temperature in the region above the combustion chambers is so high that local steam pockets are created, and these take time to collapse; in the meantime the steam pockets vastly increase the total volume of the coolant and the only 'way out' is the ejection of water/steam mix past the radiator cap. So if the amount of coolant expelled in reality is greater than ~200mL, then there's another cause.

 

Don't forget to flush the system every couple of years to flush out the oxidatiion of iron andnthe electralisis of aluminum to iron. Leaves a mess and can reduce the cooling capacity. Drove a XK 140 for hears with no problems and all my XK engines have never overheated.

 

Reply and Update from the O.P.
Thanks for your comments. I am unable to shed any light as to why the overflow from cold is so substantial, but nevertheless it is what happens. Shortly after my last post (back in 2016) I purchased TWO TR6 overflow bottle plus one chrome TR6 overflow bottle bracket. I cut the bottom off one bottle and the top off the other and was able to glue the one into the other using plumber's PVC cement. I then used the bracket to attach the thus formed double sized bottle to the lefthand lights wiring cover situated just ahead of the radiator (XK150, remember, so plenty of space and airflow). The bracket hides the joint where the two bottles meet, so it looks like one big bottle.

I have been using this successfully with no problems whatsoever over several thousand miles since 2016. Thus equipped I can check the coolant level without even opening the bonnet as the overflow bottle is just about visible through the grill. I do check the actual level in the neck of the radiator from time to time, but it is, of course, always right up to the overflow...

I can take some photos if anybody is interested.
Cheers
Tony

 

Aluminum Expansion tank installed in my XK150
On the radiator is just a sealing Cap.