Hi Folks,

I have recently been beset by overheating due to what I believe is air in my coolant system. I have gone with an expansion tank, with its own high pressure cap. Now, all I need to do is block the rad openings, since I have plumbed everything to the coolant lines (lower hose teed to the thermostat housing, and the upper to the highest point in the system - the line that went to the heater, which is not there anymore), with a non vented cap.

What cap can I order to remedy this, so that the expansion tank now has the rad cap? Welding shut the opening is not an option for me right now.

Everybody wants a make/model etc so they can order one. Somehow, my car is not in their databases! http://www.locostbuilders.co.uk/images//smilies/sad.gif

anyways, thanks again.

[Edited on 14/5/13 by RK]

I used one of these for mine, maybe you can find stant over there Stant Radiator Cap - 21-25 Lbs Lever Type | eBay

I have a similar issue with my header tank system.

Might be head-gasket, but I suspect it's in fact the thermal expansion of water is significant. I.e. airspace in header tank must be large enough for expansion or water will be pushed out of the system.

Thermal expansion of water is 4.2x10-2 from 4 to 100C.

My system is 14 ltrs, so assuming coolant is at 100C.

14*4.2x10^-2 = 0.59 Ltrs,

So you need more than 0.59 Ltrs of air space to allow for the water expansion... Any trapped air in the system will expand more than the water causing more loss of coolant...

If you have a 15psi pressure cap, as 15psi corresponds to atmospheric pressure you will need twice the volume of air if you don't want the pressure cap to vent, i.e. for my 14ltr system I would need 1.2ltrs of air above the fill level on the header tank...

Cheers

Dan

Assuming you have a radiator with an overflow spout on the filler neck just fit a blanking filler cap and and block the overflow hose.

Before you do fit a a blank bayonet fitting cap to the rad you would have to check and see if the overflow stub pipe on the cap fitting is a proper soldered in brass tube as most 1970s and 1980s british manufactured rads used a push in plastic stub pipe.

A simpler get it working fix would be to would be to cut disc from rubber insertion sheet or leather to fit between the rubber washer at the spring loaded end of the cap and the raddiator filler. This should stop ait getting drawn back in at the rad as the system cools down.

In the longer term blanking off the filer on the rad isn't that difficult, it just involves soldering using a low melting point solder.

Excellent! Thank you!

It is hopefully the last piece of the puzzle of getting my car to run properly. It might be for sale though, as I have discovered how much fun track days are in the tin top - you know, an Audi A4 Avant is a good car for that; not too powerful, but stable and takes a bit of work to pass anybody.

from memory, the austin maxi had a blank cap on the rad, and pressure cap on the expansion tank
a quick search found this list
http://www.ebay.com.au/itm/Radiator-Cap-Alfa-33-Austin-Allegro-Maestro-Maxi-Mini-BMW-2000-3000-FC53-/190602880315

(ok its in au, but good list to work from)

edit:
it is in uk, but does appear to be a pressure cap, not blanking, - oh well

[Edited on 14/5/13 by gremlin1234]