Jump to content

Recommended Posts

I have a TR 3 1956
after a good run and leave motor runIng for a few minutes some times It pushes  coolant  out of the overflow
about 250mls of Coolant wasted

I have a 4lb cap on the radiator new thermostat new hoses 

no leaks anywhere 

can anyone give  any ideas  how to stop this happening 

paul

 

 

Link to post
Share on other sites

Hi Paul,

do you have too much coolant in the system.

There should be just enough to cover the bottom of the neck from the rad. - about 1" from the top.

If that is OK then have you got an air bubble in the system - have you recently taken the system apart.

 

Roger

Link to post
Share on other sites

Perhaps it’s a little overfilled especially if it’s a regular occurrence?

the coolant just needs to be couple cm covering the bottom of the rad neck extension.

you can fit an expansion tank. I did this mod. A blanking cap on the rad a suitable hose off the rad overflow to the expansion tank And the 4lbcap on the tank

Something  like this Looks period-ish 

https://www.ebay.co.uk/itm/362989569116

 

Edited by Hamish
Web link
Link to post
Share on other sites

Hi Paul,

my profession is being a civil engineer for house heating systems I try to explain.

The pressure in any heating system is caused of two different issues:

1. The pressure by expanding water.

Take any sealed water system (heating / cooling, no matter) with NO air in it and no expansion container.

The water expands with raising temperature and the pressure raises fast and extremely.

To avoid this you need air in the system to be compressed (in houses a container with a diaphragm),

so the pressure raises more slowly the more air you have in the system.

On our TRs (and other engines) this is about 1 liter of air.

So do not overfill the system, always keep enough air in the system.

Air in there is no problem!

2. The pressure by vapor pressure.

Take any sealed water system (heating / cooling, no matter) with A LOT OF air and only some water in it.

The water vapors with raising temperature and the pressure raises due to the temperature.

edit: for details about the temparatur when this starts to rule please see later post

This is where you want to go to with a car cooling system: let only the vapor pressure rule.

The vapor pressure in the air over of a coolant / water mix 50/50 is:

4 PSI (0,279 bar) at about 78°C

7 PSI (0,483 bar) at about 90°C

13 PSI (0,896 bar) at about 105°C

So that's simple: the coolant can be hotter (the safety valve / rad cap will not open) with a rad cap with higher pressure.

To tell you the truth: I have no explanation at all how a car cooling system of ab car can work with a 4 PSI cap.

I would risk to switch over to a 13 PSI cap and add an emergency overflow bottle - but this is up to you.

This is the set up on my TR4A:

- I always let enough air in there to let the vapor pressure rule!

  edit: this is the one and only urgend thing on the temperatures (mainly below 100°C) we drive our cars

- she comes with a 13 PSI rad cap, highest temperature I ever had was 110°C (electronic gauge) without any problems

- I added the TR4A emergency overflow bottle again (was missing when I bought her), but this is always try like a bone in the desert

- I have never any overflow in there or any loss of coolant in any case

Hope this helps, Marco

 

Edited by Z320
Link to post
Share on other sites
1 hour ago, Hamish said:

Perhaps it’s a little overfilled especially if it’s a regular occurrence?

the coolant just needs to be couple cm covering the bottom of the rad neck extension.

you can fit an expansion tank. I did this mod. A blanking cap on the rad a suitable hose off the rad overflow to the expansion tank And the 4lbcap on the tank

Something  like this Looks period-ish 

https://www.ebay.co.uk/itm/362989569116

 

I have always thought that the extended neck on a sidescreen radiator is the expansion tank. 

Rgds Ian

PS if I overfill mine it dumps the excess until the coolant is just covering the bottom of the neck when it’s cold. (Just like Roger said)

Edited by Ian Vincent
Link to post
Share on other sites
1 minute ago, Ian Vincent said:

I have always thought that the extended neck on a sidescreen radiator is the expansion tank. 

Rgds Ian

It is thats why you should only fill it so you can just see water lapping as you look down into the neck that leaves plenty of room for expansion.

Stuart.

Link to post
Share on other sites
32 minutes ago, Z320 said:

Hope this helps, Marco

Marco, I just want to thank you for your generosity. This explanation is painstakingly clear and accurate.

Link to post
Share on other sites

Agree with not filling the rad to the top, but if you want more coolant in there you can fit a pressurised header tank as described above, or (as I have done) fit an expansion bottle connected to the overflow stub on the rad, pipe must go to the bottom of the bottle, & you need a rad cap which seals perfectly around the top rim.

I don't know if these are available for the TR3,(which has a deeper 2nd seal) I made my own seal for the top.

You can then fill the rad right to the top, & water simply expands into the bottle, & then gets sucked back into the rad when cooling down.

Bob.

Link to post
Share on other sites
1 minute ago, Lebro said:

Agree with not filling the rad to the top, but if you want more coolant in there you can fit a pressurised header tank as described above, or (as I have done) fit an expansion bottle connected to the overflow stub on the rad, pipe must go to the bottom of the bottle, & you need a rad cap which seals perfectly around the top rim.

I don't know if these are available for the TR3,(which has a deeper 2nd seal) I made my own seal for the top.

You can then fill the rad right to the top, & water simply expands into the bottle, & then gets sucked back into the rad when cooling down.

Bob.

But do you need that extra coolant Bob?

When we were doing the LBL Rally last year the temperature was in the high 20's or low 30's for most of the trip and it included going up and down both the Stelvio and the Gavia twice.

At no time did the temperature gauge in my TR3a go significantly above the midway point and when it did the electric fan cut in and brought it down.  I checked the coolant level every morning and it was always just covering the bottom of the neck.

Rgds Ian

PS I did have fuel vapourisation problems on one occasion though when I had to stop to wait for a large campervan coming the other way as we were approaching the summit of the Stelvio.

PPS I also have a recored radiator with the starter handle holes removed

Link to post
Share on other sites
9 minutes ago, DavidBee said:

Marco, I just want to thank you for your generosity. This explanation is painstakingly clear and accurate.

Thank you Marco an informative explanation of the theories.  I had noticed the change in the rate of temperature rise in the TR when the cooling water system is fully filled.

A sidescreen TR issue - What happens when the cabin heater is positioned highest in the cooling water circuit of a vehicle and fills with air? (think also domestic/house water heated radiators here)   No or reduced cabin heat available.   So you introduce a vent valve (domestic radiator) to remove or bleed the trapped air out of the heater matrix, thus allowing the heater matrix to fully fill with hot coolant and allow for heat transfer when demanded. 

Why do modern vehicles use a fully filled water cooling system with an expansion bottle?

Cheers

Peter W

Link to post
Share on other sites
26 minutes ago, Lebro said:

You can then fill the rad right to the top, & water simply expands into the bottle, & then gets sucked back into the rad when cooling down.

Bob.

Yes this works,

but every time you supply the rust in the engine with fresh oxygen,

this is why they switched over on house heating system to a expansion container with diaphragm decades ago

Edited by Z320
Link to post
Share on other sites
1 hour ago, Z320 said:

Take any sealed water system (heating / cooling, no matter) with A LOT OF air and only some water in it.

The water vapors with raising temperature and the pressure raises due to the temperature.

This is where you want to go to with a car cooling system: let only the vapor pressure rule.

The vapor pressure in the air over of a coolant / water mix 50/50 is:

4 PSI (0,279 bar) at about 78°C

7 PSI (0,483 bar) at about 90°C

13 PSI (0,896 bar) at about 105°C

So that's simple: the coolant can be hotter (the safety valve / rad cap will not open) with a rad cap with higher pressure.

To tell you the truth: I have now explanation at all how a car cooling system of ab car can work with a 4 PSI cap.

 

The figures you quote are for gauge pressure  Marco - you have forgotten to add on ambient pressure. With a  4psi rad cap the pressure on the coolant is 4+15 = 19psi absolute, making the equilibrium/boiling point about 107 degrees (give or take for the glycol content). 

Edited by RobH
Link to post
Share on other sites

Yes,

with the coolant 78 deg C hot inside the rad the pressure is 4+15 PSI absolute,

while outside the rad, under the bonnet the pressure is 15 PSI absolute?

So 4 PSI is the overpressure.

 

If there is any interest about I post a simple everybody-experiment this evening 

Link to post
Share on other sites
47 minutes ago, Z320 said:

Yes,

with the coolant 78 deg C hot inside the rad the pressure is 4+15 PSI absolute,

while outside the rad, under the bonnet the pressure is 15 PSI absolute?

So 4 PSI is the overpressure.

 

If there is any interest about I post a simple everybody-experiment this evening 

Yes I am interested Marco.

Peter W

Link to post
Share on other sites

You are forgetting that the calculations of vapour pressure are for a sealed system Marco.  It doesn’t start from ambient pressure, it starts from zero.

At 78C the vapour pressure would be 6psi in a sealed system but in the radiator there is already 15psi of atmospheric pressure present so this excess pressure causes the vapour to condense back into the fluid. No vapour pressure can be added to the system until 100C is reached, where vapour pressure equals ambient pressure. At this point vapour ceases to condense and the pressure in the system starts to rise.

The extra pressure one experiences when removing the rad cap from a hot engine is mainly due to expansion of the water and air - not to vapour pressure.

Link to post
Share on other sites

Hi Rob,

thank you very much for your veto.

That let me have a closer look on the facts apart from that what I believed as the fact.

And this is a absolutely wonderful and humblene example how something that someone has been convinced about is wrong.

Because you are absolutely right,

the vapor pressure is below 1 bar / 15 PSI atmospheric pressure as long water is only 100°C hot, coolant mix 50/50% is below 105 - 110°C hot.

This meens for me:

- the only importend thing is always to have enough air in the system to be compressed by the expanding water

- it is possible to use a 4 PSI rad cap up to about 115°C coolant (50/50 mix) temperatur (vapor pressure is then about 15+4 PSI)

- a 13 PSI rad cap allows about 125°C

Allow me to stroke everything on my post what is not correct, so others can see what is right / wrong.

Experiment comes later, I have to make photos.

Ciao, Marco

Edited by Z320
Link to post
Share on other sites

Here are the photos.

As you can see by the pencil I do not overfill the rad.

P1160691-b.JPG.84573ca89032b38f18379fa91347d753.JPG

The diameter which gives pressure (and force) on the rad cap is some less than 29 mm wide,

that is about 1 1/8", the expanse of the diameter is pretty exact 1 square inch. Possibly this is not only by accident?

Next you see two rad caps, a 7 LBS (PSI) one, not in use, and the 13 PSI one from my TR4A.

P1160692-b.JPG.7570a00ee93ed01e79254b8564d48af2.JPG

When I press the seal down I can feel the different load of the springs,

on a scale, for example our bathwoom scale, I can play with it and see the load when it opens.

You have to try several times to got the feeling for it.

P1160694-b.JPG.c520593128a98688b080ef6f7b75d98d.JPG 

The 7 LBS cap opens at 4,5 kg, that's about 10 LBS, so this is about 50% stronger as stamped on it.

The 13 LBS cap opens at 6 kg, that's exacly 13 LBS! Well done, the 7 PSI cap with 10 PSI is no problem in my opinion.

Is the other way around also possible, a 4 LBS opens at 2 LBS?

What do you think about?

 

Edited by Z320
Link to post
Share on other sites

Why not convert to a modern system with remote header tank?

See my article in TR Action 112, or section B18 in the Technicalities CD.

I think that exceeding a setting of 7 psi is not a good idea as it over-stresses the hoses.  With a remote header tank, a 7 psi cap on the remote tank is quite sufficient, and 4 psi would not be a problem.

Ian Cornish

Link to post
Share on other sites

Indeed this 7 LBS cap is very special,

it reaches not deep enought down in the radiator nack, so it never seals it.

A 100% product of "we don't know what we are producing- but we do it anyway"

Edited by Z320
Link to post
Share on other sites

I made an opportunist purchase if a 7lbs rad cap locally last year to replace my 60 year old 4lbs cap and the composite head gasket blew in a minor fashion three weeks later.

Are these two events related?
 

james

Link to post
Share on other sites

I never had this, so just 3 thoughts.

Isn't the damage on a blew head gasket the heat and pressure from the cylinders, this is much more than 7 PSI?

My TR4A had that 13 PSI already when I bought it 11 years age, and probably also the 17 years before with the previous owner. This works without problems.

13 PSI is only the max pressure, you don't have that automaticly / always with the cap but with the missing air in the system (to be compressed by the expanding coolant).

What a lovely idea: I will fit a coolant pressure gauge on the car to see what the pressure does!

 

 

Edited by Z320
Link to post
Share on other sites

I'd still be interested to know what the top-hose water temperature is, after a run and during subsequent idle on a day when it blows water.  I had the same issue until the the radiator was re-cored* several years ago.  I use a 4lb cap with no separate expansion tank or other modifications.

*without the start handle hole.

Link to post
Share on other sites

I had overheating at over 60 mph because the engine rebuilder ,at the Seven Dials in Brighton, failed to set the liner heights correctly in spite of having the copied page from the manual delivered with the engine.

I then uprated the radiator with extra tubes and fins. I tried a 7lb cap and water leaked from the water pump, the heater hoses and the lower radiator hose. 4lb cap was OK. 

I then fitted an expansion  tank with the input at the bottom and a 4 lb cap and the radiator has a blanking cap only. There are two different lengths of cap and it is ,of course,  important to get the right one for your tank.

So I fill the radiator to the top and have about 1 1/2"  in the bottom of the expansion tank. It all works really well even though the expansion tank is lower than the rad filler.

Link to post
Share on other sites
49 minutes ago, mikej said:

I'd still be interested to know what the top-hose water temperature is, after a run and during subsequent idle on a day when it blows water.  I had the same issue until the the radiator was re-cored* several years ago.  I use a 4lb cap with no separate expansion tank or other modifications.

*without the start handle hole.

You could add a sensor in the thermostat housing for a low price LCD gauge in the car

post-13222-0-71417700-1523820126_thumb.jpg

post-13222-0-63164100-1523820137_thumb.jpg

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.