With massive thanks to Marty, yesterday we swapped my heater box, core, and replumbed the whole cooling system... by chance, we found the cause of my cold heater at idle, and it wasn't the LPG plumbing.
Heater box and core swap was the straight forward bit. It was when we got to changing the heater return and expansion tank line as I'd said about to put the vapouriser in series with the heater and simplify things a bit, Marty decided to remove the thermostat entirely to fit a hose on (coolant all drained as I had new top/bottom/pump hoses to chuck in too). Then he saw this...
Just cut it apart to see from the other side:
Pretty thick defect:
That be the heater/expansion return port... as you can see, not much is getting through that!
As luck would have it, Marty had a new spare Britpart or possibly Bearmach stat in his stash, so we took a chance on that, and put it back together leaving the LPG in parallel. The ID on the ports on my OMVL vapouriser is really, really small. Given the restriction on the stat, it seemed logical to stay parallel. Because my car is weird though, the expansion/heater return hose wasn't standard, and doesn't look like the normal Thor part, so we improvised and lost the metal pipework and old rubber hoses. It's nice a simple now, just need to get a 19-19-19mm T to replace a few bits we had to stick together to join things up.
Most importantly... no leaking heater, and heat at idle! Plenty of it. I was quite excited :)
Southampton with a Nanocom for Thor/GEMS P38s
1996 4.6 HSE, then became a 4.0, now cubed.
1997-8 4.6 HSE Motronic/Wabco prototype vehicle. Now M57 powered. Still auto.