Interesting about the water levels being different. My Chummy had what you would call a modern core, the ‘zig-zag’ pattern that I ran for 28 years. Three years ago I thought I would give her a treat and had a new original pattern core with new top and bottom tanks made up (the price still brings tears to my eyes). At first I thought I had a leak as I was putting in much more water than I had previously with the other core. It blows it out of the overflow pipe until it is about ¾” above the core and then stays at that level. However I cannot resist filling it up on a regular basis because it just seems too low, though it never overheats. Strange that it should run at different levels in different cores. Any ideas?

.

Ian,

I would hazard a guess that the overflow was set low in the top tank when the radiator was rebuilt. It should not be too difficult to soften the solder and raise this (if you had a mind to) with the rad removed from the car.

Another point with a modern core is that it cools more efficiently. I run with thirty percent of mine blanked off with a piece of talc, except in the hottest weather. Runs at about 85 deg. normally.

Mike

G'day Ian,
It is all the fault of "Boyle" and his pressure/volume/temperature laws. After filling the system entirely, when cold, a "run" heats the water which then expands and chucks the surplus out the overflow. Now, while still "running", the entire system is still full of expanded water - no gaps. After stopping & cooling down, the water contracts & sucks air in to the equivalent expansion volume change (if there is no way in for air, it will compress the hoses etc). When you check the level, you let the air in, and sure enough, it is just above the core, but you are hot checking it at normal running temperature (which is not recommended as it can get quite exciting!), when the level will be "full".

As to why it is different after the re-build is all a question of volume & shape, temperature & pressure. for example, the smaller the top tank, the lower the cold level will be. Since you had new tanks made up, there may be slight dimensional differences.

Of course modern cars solve this problem with either a remote header tank, or a watter bottle that collects the ejected water when hot and sucks it back in when cold so the system always looks full.

I hope this helps.
Cheers,
DG

A bit Extra.....

As well as header tanks and expansion bottles , moderns also take advantage of the aforementioned thermodynamic laws by running with a pressure cap. This raises the pressure in the system (because of the expansion) and allows more "heat Energy" to be taken by the water before it changes phase to steam.

A bit like the dear old pressure cooker.

Steve.

p.s Although not yet on the road, during sea trials the colander also chucked out its coolant to a level around about were you say, and coincedentally I too have a modern core fitted.

Thanks for your input so far, for the record the Rad is an exact replica of the original Austin part in all respects, I have just checked the overflow (something I hadn’t thought of), it ends level with the bottom of the thread for the cap so cannot see a problem with this.

.

That's OK then!!!

but was worth a look.

win#

Don't know what type of radiator is on my Chummy, but I have the same problem - especially in the summer down here in south of France. I too kept filling it up, just to see it dribble out the overflow. Thanks to Dennis from OZ, I will no longer have sleepless nights over this issue!

With reference to the expansion with heat, how much actual expansion is to be expected?. My 31 Box coolant seems to verging on the boiling after only a 10 minute fast idle whilst tuning the engine. Rad has the clip on type of cap which lets out a lot of pressure (and hot water!) when released. Steam was previously observed coming out of 2 opposing small holes in the header filler just below the level of the sealing washer. Thus when driving along, steam was happily escaping via these holes like the Flying Scotsman!. In my ignorance I filled these holes in to stop this but now I have the pressure build up.

Is this an indication of a blocked rad? Just wondering if the holes were drilled by a previous owner to relieve the pressure caused by overheating?

Is there not an overflow pipe? I bought a seven some years ago and found it was blocked with all sorts of rubbish, I used a net curtain wire to clear the tube, now any steam escapes down there and of course conversly prevents a vacumm building up when every thing cools down - just as important.

Naomi, just back from holiday......

I saw water escaping via the overflow which I put down to the expanded water reaching the level of the overflow outlet in the filler cap so assumed it was clear. Good point though so will check that out.

No obvious obstructions in the overflow pipe so I guess the rad will have to come off for a proper look

I'm no expert, David, but it certainly sounds to me that something is not right somewhere. You shouldn't get pressure building up in a thermosyphon system, and for your engine to be getting to near boiling after a short run at tick-over suggests that something is amiss somewhere. Don't forget to flush out the head & block whilst you're at it.

There was an item in the Essex Clubs magazine about a year ago which showed the side water manifold was basicaly completely blocked with rubbish.

I 've found two of my blocks had hardly any opening in the water jacket between the bores, the heads were not much better. I managed to disturbed a great deal of rubbish from the block in one case.

That is an advantage of the screw in core plugs, easy to get into the block and then seal it again.

Let alone what might be blocking the rad care...

Naomi (still sunburnt, but salsa's fun in Cuba, and there was a Jazz festival as well).

My 33 box's engine has got screw-in core plugs on the block. Am I right in thinking that they were discontinued in about 1927? It must be a bitsa because the crankcase is a '35.

Still getting my head around the physics thing. If there was a blockage say in the rad, this would cause the overheating. Then the water would expand but the pressure should vent overboard thru the overflow pipe?
I have been careful not to overfill as pre previous posts.

I have certainly seen water come from there so assumed the overflow pipe was clear. (I have yet to try the curtain wire trick)

Has anyone found the 2 holes in the filler neck below the level of the clip on cap seal thus allowing water/steam to excape from there? Or is that a bodge to try and solve aformentioned problems

Hopefully mysteries will be solved when I dismantle at the weekend

Having removed the rad, flushed everything thoroughly, cutain wire through the overflow, all I could find was a slight kink in the bottom hose. The side water branch elbow is angled such that the dynamo is in the way of a natural curve of the hose causing a flat spot. Didnt look that bad but I suppose it must have had an effect cos it all seems OK now. Replaced with one of those flexible jobs to get the bend underneath the dynamo