Overheating, losing coolant but not sure why...

Hi everyone,

So the new engine is in, running very nice with no oil problems so far. Fingers crossed.

However, now I am having overheating problems on stop start/traffic journeys. I have done the following:

- checked thermostat - working fine
- replaced both radiator caps with sprung ones (not the normal type)
- bled the system (and do this every time it needs more coolant) using the funnel and pipe process with the bleed nipple under the driver seat, squeezing hoses, etc.
- run up to temp both before and after a drive to check for leaks, none seen
- flushed radiator, top and bottom pipe run hot

I can't figure out where I'm losing coolant. There's no gunk in the filler cap now. The only thing I can think of is that the front radiator cap needs to be a normal one and not a sprung one - could that be the problem?

Any ideas?

Big debate about this, my 2p worth is don't use a sprung one there. Others may disagree.

For the £2 a new one costs it's probably worth replacing.

Any other ideas?

Right well I found the problem, the bleed nipple was bust. Of course I couldn't see the leak until the other half had a look after a ride and it was right there... I think the van did it on purpose to make me look stupid. Anyway it's fixed now, and I can confidently say that it's running the way it should. Sounds great, no smoke, no gunk, no overheating. Like a Hijet dream! After a LOT of effort (and help!). So thanks everyone!

The sweet smell of success -  or the smell of hot anti-freeeze in your case. Well done  to both of you for all your perseverance. I was 100% happy that the engine was a good one. 

I just got the Invoice from Hampshire Freight Saturday morning for sending the engine up to you.  I had better get that promptly  paid today in case I need them again.  Although it is now unlikely that I will carry on with the Hi-Jet business when I can hopefully can get back to the Garage. I haven't been there since the Stroke. 
My wife and son have been picking up the letters and checking the Security Cameras  for unwanted visitors.