Fluid exchange.

Filled the cooling system last night. All worked as planned. Appeared to have self bled too.

I spent a while pressuring the system to check for leaks, fixed a weap or two. I attached a foot pump to the header tank connections I added for this reason. I used some rubber tube and a old tyre valve and some hose clips. I attached the fuel pressure gauge in the cabin to the cooling system. This enabled me to "blow-up" the cooling system, not literally...

Anyway tells me the system blow's off at 17psi. As planned.

It also told me I had a small leak somewhere, or a couple of microscopic leaks.

I blew the system up to 15psi, left it for 2hrs for a leakdown test, this showed pressure had dropped to 13.5psi. I then deflated it and went to sleep.

Today I looked around for small spots of coolant on all the alloy parts...The coolant I am using is OAT, its bright pink so easy to see.

I note two microscopic drops of coolant on a weld on the headertank, so there is part of the answer. Although these are only equal to about half a drop of coolant in 12hrs (2hr under pressure-10 static), quick blob of TIG will sort.

Also there is a tiny leak on the water rail flange at the cylinder head...This only happens over 10psi, but will need to be fixed. I tried to fix it by "twatting" the flange with a blunt object in a dodge attempt to force a seal...thats worked for me before!

I need to whip the water rail off again once the system has been run and assessed as to the pressure and flow in different areas... to plumb the heater system, so I will cut off the 5mm flange and make a new one from some 10mm and get that welded on...

This is a problem on caterhams too, the flange can really only be one shape with two bolts, ideally it needs 3 bolts or 4 to even the stress on the flange. I have the original cast flange here I cut off the original water outlet, that might be weldable, the cast material is stiffer than alloy sheet you see. Anyway bar that it's ok bit of pain removing the strut brace and header tank again but, hey ho.... I decided to try the twat it approach after realising that replacing the flange was probably the only decent fix.

I'd just like the cooling system to hold pressure like a tyre, thats not too much to ask, no?