New pipe run is now complete.
First pic is looking up from under the front towards the new access hole.
This one shows pipes going back towards fuel tank. Zip ties are temporary until I can get a permanent solution.
Looking up towards the original shut-off valve. The vertical pipe is now deleted and needs removing. There are shut offs on the flow, just before the coolant pump, and on the return just before the coolant goes back into the engine.
Sump is on the left. Shows new pipes finally connecting to the pump outlet and the return to the engine.
So I ran the engine up to about 175F. I added 7 gallons of coolant. I ran it with the cap off and kept topping up as the fluid level fell below the sight glass.
On my recent trip to the weigh station, I think I lost 5 gallons of coolant through shut-off valves that weren't "shutting off" completely. The engine remained in range for all but the last 1/4 mile where I thought it was de-rating and I noticed the gauge rising just before I pulled into the yard.
All seems well now. Coolant is replaced and there appear to be no leaks at all from the new pipework (or anywhere else).
Front heater is blowing very hot.