Coolant Use

[Wheelz]

Simply raising the level of the expansion bottle may not achieve much for two reasons:

1. Because of the way it is plumbed into the system. The coolant in the bottle is still below the entry point into the radiator so coolant may not flow into the rad to fully top up by gravity.

2. Also the end of the metal expansion pipe inside the radiator is not at the top but goes down into the coolant, and so any air in the system cannot escape as it would with a higher level 'header' tank.

Just for my own sanity, one day I will get round to making an illustration, as they say a picture is worth a thousand words!

[DJT]

If you want a diagram of a simple HT installation for a Stag, then here it is. No need for the over complicated bling supplied by the two companies who sell them.

This works:

1. Raises the coolant level above the water pump, ensuring supply of coolant at all times.
2. Thermal circulation occurs through the HT - you can see it happening.
3. Instant confirmation of the coolant level as soon as the bonnet is lifted.
4. Easy filling of the coolant system with little chance of airlocks.
5. Any local radiator shop can add the two spigots for a small charge.
6. Brand new Volvo HT can be purchased online for about £50, including internal float switch for low level alarm. I bought my original one from a scrapyard for next to nothing, but have now replaced it with new.
7. 12v alarm/buzzer readily available online. Simple bracket to hang HT from strut mount easily fabricated.



I have been using this for the past 15 years (54,000 miles) in my current Stag and a further 3 years (12,000 miles) in my previous Stag. No overheating - even when a head gasket was failing in 2013. Kenlowe fan has only come on once (briefly) in that time, in a traffic jam on the M5 in 30 degrees C after a prolonged high speed run in June this year. OE viscous fan fitted.

Screenshot 2023-10-18 at 11.17.09.png

[Wheelz]

Great stuff David. A picture is worth a thousand words but you just beat me to it! Here is my version of the comparison of raising the bottle, with a header tank system.

IMO the feed from the HT doesnt necessarily have to involve fitting a spigot to the rad. but it is a nice way to do it.

Firstly the raised bottle idea: This does not work as a header tank because the level in the bottle is below the top of the radiator, so it cannot top up by gravity..

Note that level check and top up in two places is required. Also, any air in the system can get trapped in the top of the radiator and will not automatically bleed out.


image.png

[Wheelz]

Compare the expansion bottle system with the header tank system shown below. Note that there is only one level check and top up point. Also any air in the system will bleed automatically, and replaced by gravity fed coolant, so the radiator should always be kept full.

image.png

[trunt]

I soldered the fittings onto my radiator tank myself, having a bit of confidence from years of plumbing around the house. I got some PEX barb connectors as they are brass and have a nice flange to give the soldering some strength, and cut of most of one side that went inside the rad. Some real lead solder and it was not terribly difficult. Though I'm sure a UK rad shop would do this, here in USA old style radiator shops are few and far between and not so cheap..



.

[DJT]

Compare the expansion bottle system with the header tank system shown below. Note that there is only one level check and top up point. Also any air in the system will bleed automatically, and replaced by gravity fed coolant, so the radiator should always be kept full.

image.png

So simple and effective it makes you wonder why some commercial suppliers have persisted with an over complicated system for years

[richardthestag]

Lord help us. He is on his soapbox again.

with an eewp and no real need for the radiator to be brimmed, Surely the "trapped air" is useful for the expansion of the coolant as it heats and subsequently cools. What is the difference between that and the large shiny external vessel?

I have never understood the obsession with "trapped" air in the top of the radiator.

a low coolant sensor could be easily installed to alert when coolant gets too low. top hose or maybe a reed switch fitted into a boss soldered to the side tank of the rad itself.

Alternatively, a squeeze of the top hose when cold should help you tell if it has coolant in it, and a glance at the OE expansion bottle will tell you if the level is correct. too high a level and you may then need to check the top of the rad and also understand why the coolant is not being drawn back into the rad as it cools.

a true HT on the hot / inlet side of the rad could and, Did for me, allow coolant to bypass the radiator. Is this why most are plumbed into the cold / outlet side of the radiator and as close to the rad stub as possible?

a high level and better (than oe bottle) quality plastic vessel, so the level can be seen at a glance, is a cheap and effective upgrade to the stag coolant expansion vessel connundrum.

Nice, cheap and oh so simple.

[Wheelz]

I have never understood the obsession with "trapped" air in the top of the radiator.

With a high level water pump, having little concern about a drop in coolant level seems a tad reckless?

[richardthestag]

With a high level water pump, having little concern about a drop in coolant level seems a tad reckless?

But the OP doesn't, hence my original question about EEWP and H"le"T being belt and braces

If you were so massively concerned you might suggest that owners unsolder the expansion pipe and resolder it flush with the top of the rad. No trapped air then is there? even cheaper and easier. Do it at home with a basic kit of flux, solder and blow torch that heating engineers across the country use.

So when there is no trapped air your solution would be.......

[Wheelz]

If you were so massively concerned you might suggest that owners unsolder the expansion pipe and resolder it flush with the top of the rad. No trapped air then is there? even cheaper and easier. Do it at home with a basic kit of flux, solder and blow torch that heating engineers across the country use.

No, I wouldn't want to knowingly mislead anyone to do something that would not work.

Try it for yourself - you will find that even if the pipe was moved to the top of the rad, the coolant in the expansion bottle will still NOT flow into the radiator by gravity. (hint: the coolant would not run uphill by gravity).

To achieve a reliable gravity feed, the coolant feed pipe into the cooling system should not run uphill as you suggested. That is why the guys have fitted a spigot to the rad lower down so that it can top up by gravity. It is also advisable IMO to have a return pipe to the 'header' tank that allows air to be removed to make space for coolant.

[richardthestag]

No, I wouldn't want to knowingly mislead anyone to do something that would not work.

Try it for yourself - you will find that even if the pipe was moved to the top of the rad, the coolant in the expansion bottle will still NOT flow into the radiator by gravity. (hint: the coolant would not run uphill by gravity).

To achieve a reliable gravity feed, the coolant feed pipe into the cooling system should not run uphill as you suggested. That is why the guys have fitted a spigot to the rad lower down so that it can top up by gravity. It is also advisable IMO to have a return pipe to the 'header' tank that allows air to be removed to make space for coolant.

If the system setup and functioning as the factory designed it then, maybe it is magic but it does work. The factory did not design the system with a gravity feed in mind. BUT if you so wished to have a gravity feed from an expansion vessel then it can be achieved within the cost of a round of drinks. at Wetherspoons of course.