Coolant level in radiator.

[Markvh]

Probably another daft question!
I always top up the radiator (Mk2 Stag) right up to the brim. Now, I know that there is a slight leak of coolant into the vee, but whenever I take the rad plug out, the water level is approximately half way up the top hose. if there wasn't a coolant leak should the water level be higher?
What I don't understand is that the overflow pipe across the top of the rad to the expansion bottle passes below the top hose. So how can the coolant suck back from the expansion bottle to a higher level than the overflow pipe?
I could understand this might work perhaps if you have a perfect vacuum in the system with not the slightest air ingress and the pressure that is built up in the expansion tank due to the expansion of the hot coolant is retained long enough to help push the coolant back into the rad and into the space above the overflow pipe.
Surely in a 37 year old car it will be virtually impossible to maintain a 100% sealed system?
Is my thinking correct or am I missing something here?

[V Mad]

Mark, its not a daft question at all. The system does rely on being completely air tight or it all goes pear shaped. Many stag owners are still operating with the original system, and see no reason to change, but many other owners have changed to a high level tank which keep the system topped up by good old reliable Mr Gravity.

I hesitate to use the common term hea*er tank as the mere mention of the words can cause the forum to erupt. When you are a full member you can search and you will find lots of info as well as all the 'banter'.

So its your choice whether to keep it original or fit a ****** ****.

PS: top hose half full is typical with original system.

[Lingen]

Mark. It is a common misunderstanding, but the coolant is not sucked back into the radiator. It is designed to be blown back by the pressure that should build up in the expansion bottle as the engine heats up. If the system has the slightest leak anywhere, and this pressure falls away, then the level in the radiator will not be maintained. It can't be sucked back as this would cause a vacuum in the expansion bottle, and the top hose would probably flatten first. The level you are getting in the top hose is probably level with the end of the pipe from the bottle where it enters the radiator, and this seems to vary a lot. If you can get the system properly airtight, it usually finds its own level and then stays there, or that is what I found anyway. A header tank-properly piped in- which many are not, is the other option.
Mike.

[V Mad]

It can't be sucked back as this would cause a vacuum in the expansion bottle,
Mike.

Not quite true as the pressure cap has a valve which opens to allow air into the bottle.

[marshman]

Not quite true as the pressure cap has a valve which opens to allow air into the bottle.

Chris is correct radiator caps have an air inlet valve, sometimes called a low pressure valve or vacuum valve to let air into the system. See pic.

Roger

radiator cap.jpg

[Lingen]

You are right there, but have you ever tried to see how much vacuum you need before that valve releases? I suspect a soft top hose might flatten first. Mike.

[Stagsongas]

Eventual failure of that valve could be one reason why expanded coolant does not return to the system.

As has been said, if the pressure in the original expansion bottle is not greater than the pressure within the system when it has cooled, the displaced coolant will not return. If the valve reduces that pressure, a problem arises and we end up with an unintended effect;

Effective pumping out of expanded coolant over successive hot/cold cycles which never goes back to the system, and a less than full top hose.

Regards

Steve

[Robin Searle]

On topic somewhat,my AF/water system which was only two years old had a tendency to need a top up occasionally, but no leaks could be detected,but when I removed the two hoses to the thermostat and water pump,noticed with horror the aluminum edges were corroded away somewhat, then with me wondering what was actually going on inside my aluminum engine?? The result of digging through alternatives brought me to deciding to use Evans Waterless, as we do have some 35C degree days in the summer months and minus 35C in the winter.I removed all the hoses except for the in and out heater hoses,removed both drain plugs below and the radiator.Ran my compressor and blew air into the heater hose and waited until all the AF/water had gone,blew through thermostat and water pump connectors,hooked my shop vac hose to the rad with the tap removed,left overnight and no drips evident.Filled with 3 US gallons [ smaller than Imperial ones] of Evans Waterless,with the balance going into the overflow bottle.This past weekend the Toronto Triumph Club had an event in Elicottville New York and as it took 11/2 hours to cross the border, my Stag was the only TR not to overheat,needle was on N even with the engine running all the time in order to keep moving up the line.
No pressure in the system,can even remove rad cap whilst engine running,no freezing at minus 40C or boiling up to 180C, and never needs changing.Now have 1,200 miles with it and am impressed when a car renowned for overheating does not, and her brothers of all TR models did.

Maybe in the UK you do not get those temperature extremes that we 'enjoy', here in Canada but it was those images of the corrosion of the aluminum that pointed me in this direction and happy that it did.

Steve if your car had wire wheels it would be a twin of my 73 Stag, now fitted with the ZF auto gearbox so no more BW clonks, and at 70mph engine only turning 2,000rpm rather than the 4100 with the BW.

Cheers from Canada

Robin

[Staggard]

There has been a lot of talk on waterless coolant, I personally do not see it as answer to Stags overheating or corroding plus the fact its bloody expensive. I have run mine on Bluecol for the last 4 years and the PO did the same for the 27 years prior to that, temperatures here spend a lot of the time around 35 deg and commonly rise to the lower 40s . My temp gauge normally sits on the E. I have just removed my heads after 40,000 mls without a problem. I change the coolant every 2 years and take the opportunity to flush out the system. I guess its each to his/her own but for me the huge drawback for me is ( apart from Bluecol working perfectly well) if something in the cooling system went AWOL and dumped all that money in the road I would probably be temped to take my own life

[V Mad]

H2O with a good additive gets my vote. It works well and saves me money.

[KOY 23]

You are right Chris. Malt whisky is a good additive.

[DJT]

You are right Chris. Malt whisky is a good additive.

Mine's a double.......

[Stagsongas]

Steve if your car had wire wheels it would be a twin of my 73 Stag, now fitted with the ZF auto gearbox so no more BW clonks, and at 70mph engine only turning 2,000rpm rather than the 4100 with the BW.

Cheers from Canada

Robin

Robin,

I LOVE my ZF!!!

For me it has transformed the car, no clonks into gear, better shifts and more flexible gears depending how the kickdown is set. And then there's the OD RPM, so much lower. That gives me extra pleasure as I know it is saving engine wear, fuel and less heat is released as a result. Win win, win win....

Wire Wheels - Hmmmm, I remembered the hours I spent cleaning them on my S1 E Type and chickened out. Maybe I'll weaken yet...

Best Wishes from UK

Steve

[Robin Searle]

I agree that it is not cheap,here it costs around $200.00 but seeing the corrosion on some of my connectors and also watching Jay Leno who has a real extensive collection of cars,including buying the Bentley fitted with the Merlin Engine from the UK. ; https://www.youtube.com/watch?v=KRLXKW2ph0w with his Dusenburg and AF caused problems on aluminum and stainless steel.

To each his own but compared to all the other TR models that could not take the heat, mine with the reputation of overheating I was convinced I made the correct choice.

Cheers

Robin