Coolant Overflow

[flyboy]

Hi everyone,
I’ve done a couple of thousand miles now in my rebuilt Series II and love driving it. I’ve had very few issues, but just want to clarify about the cooling system.
The radiator it came with isn’t an original one…It has “Coventry Radiator” stamped on it which I wasn’t able to find out much about. It’s about the only thing I didn’t replace or rebuild.
On long trips on the motorway, it seems to overflow. When I stop, there’s a puddle of frothy green coolant under the car and coolant thrown all over the engine bay.
I think I made the mistake of initially filling it to the brim, which I now realise without an overflow tank isn’t right.
Ive topped up the coolant to just above the tubes and when I look down the radiator cap, there’s a definite flow with frothing going on.
My radiator cap doesn’t seem to be air tight either, definitely no pressurising going on.
Can anyone shed any info on this and if it’s normal…?

https://uploads.tapatalk-cdn.com/20231022/d55950d7f720705535d1b84d23337bab.jpg

https://uploads.tapatalk-cdn.com/20231022/5691a9e39e36507df09e862460355172.jpg

https://uploads.tapatalk-cdn.com/20231022/522cb23c4f762b055ca51ab752ec1057.jpg

[JDNSW]

As you point out, this is not the original radiator. I do not recognise it. It looks to be designed to have an external pressurised header tank, similar to those used on the later 90/110, or possibly is designed to be unpressurised but only to be filled to the screw thread. As you correctly note, that cap does not provide a pressure seal, but looks to provide a seal between the upper and lower part of the tank - but has an open connection between them through the cap (very strange to me).

The normal operating temperature of the engine (75-80°) does not absolutely require pressurising, but without pressurising will require regular topping up due to evaporation and may boil when worked hard. Remember that this system was designed to use water not 'coolant', and required regular topping up until an unpressurised overflow tank was added in about chassis suffix 'C'.

In my view, while it would be best to change to the correct radiator (but these are very expensive), your current system should remain satisfactory provided that it is checked daily and topped up as necessary. If the level is kept at the threaded bit, there will probably be no overflow. In this case topping up should be with water (preferably distilled or rain water).

[Gippslander]

Just a thought the circular attachment to the right of the filler, does it have a hole in the side that a copper tube would attach to. My thoughts are the cap is not meant to have holes in the top. Thus if that is the case it is designed that the upper section of the radiator above the threaded cap is designed to be the expansion tank. You would fill to level with the thread then during operation the expanded water would occupy the header tank then resort to level when cold. There is no internal pressure in the system the upper section is designed to accept the expanded fluid and lower when cooling. A pipe is attached to the dome on top of the radiator to allow excess water to bleed out of the system.
I seem to remember something like this on an old Commer truck from the fifties, so to that end I rang Warragul Radiators who have refurbished both of our rebuilds. I asked the question and was informed this was common on early vehicles to which he added he had just repaired an early Riley with this type of arrangement. He then went on to mention Coventry Radiators as a manufacturer of these systems.
I would check if the domed attachment has access to the upper section of the radiator and if so fit a bleed tube to it then patch the holes in the top of the cap and see how it goes from there. Just make sure it can vent to atmosphere through the bleed pipe.
Hopefully it then will operate more efficiently and once it has found its level only require minimal topups.

[flyboy]

Thanks John and Gippslander for taking the time to respond.

There is definitely no breather/overflow from that centre dome and the holes in the cap look like they are factory. There is however a small bleed/breather tube inside the fill hole…

If you look in this photo at the bottom.

https://uploads.tapatalk-cdn.com/20231023/8db4673f7098896b06b5f5e420a443a6.jpg

[flyboy]

That bleed tube comes from the direction of the dome…

[Gippslander]

Fascinating so no bleed tube just an internal header tank fills through the cap and the system is not pressurised. Glad you showed us this system we see new things everyday.

[gromit]

What's inside the lower section of the radiator cap ?
You can see rivets in the picture, just wondering what's being held in place.

Is it a pressure relief valve in the cap that's failed ? If so this would explain the lack of pressurisation.

Problem would be finding a replacement as it's an unusual radiator.


Colin

[flyboy]

Thanks Colin,
Will have a look in the morning and get back to you…

[flyboy]

Ok,
Radiator cap rivets are just part of the cap construction. Nothing modified or missing there.
I did however take a closer look at this fitting…

https://uploads.tapatalk-cdn.com/20231025/74866997b34000a72a2598bf6d7d41fe.jpg

And with paint removed, found that a 1c piece has been soldered on [emoji51].

https://uploads.tapatalk-cdn.com/20231025/2981662afee75ae44c417a9f63c89798.jpg

I’m guessing an expansion tank would screw on here? Any ideas?

[gromit]

I think the top section of the radiator is the expansion tank just not sure how it works.
Obviously at the moment it doesn't work !

Colin