Great info!
I was looking at this thermostat while I was building my Exocet since I have no heater core. I decided not to bother since the benefits of the bypass with a BP6D head gasket seemed controversial. I ended up just running a running a bypass hose between the heater core ports.

This page is an interesting read as well:

'+'

Which give us this image:

http://web.tiscali.it/elise_s1/statal3.gif

"To PUMP' would be from the head
"BYPASS" would be to heater core (with the opposite end of the HC routing to the mixing manifold per stock config)
"TO RADIATOR" would be to the top of the radiator.

Cold, the water leaving the head goes through the heater core only
Once warm enough, the thermostat opens, and heat core is still getting some flow
Once hot, the heater core is cut off except for metering holes, and radiator gets the vast majority of flow

Unless I am missing something or am overly tired, that works, right? The "pressure relief" part, I'm fuzzy on that tho. Not sure how that plays into the operation.

Yes.

For the vast majority of all road-worthy cars, the traditional rear-therm reroute will suffice.

Also, I recant my last post. The idea I put forth there is no better than a traditional rear-therm.

That having been said, I encourage ingenuity. I sketched up a quick diagram. If you want to build the absolute ultimate cooling system, which cannot possibly be improved upon (assuming an OEM-style water pump), then build this:

https://cimg9.ibsrv.net/gimg/www.mia...cbedeb8535.png

Joe, Thanks for the diagram. What I am trying to do is to avoid buying an "expensive" (that's relative I guess) rear spacer in the hopes that costs are reduced. Use the front neck in the rear (no thermo) and use a 'cheap" bypass ($15-20 sure counts as cheap) like the Rover unit to handle thermostat and heater core connections.

I think they way I proposed it would work, perhaps at the cost of reduced heater function once hot. Not sure that's acceptable though.

I'll play with those two pieces when they arrive and see if that sheds any light on usability.

The first one arrive, the metal body unit. It does in fact seal off the angled port when the thermostat opens so the only way to make it workable would be to drill some bypass holes in the angle port disc which would maintain coolant to the heater when the thermostat opens. The angle port disc is spring loaded (the "pressure relief" feature) but coolant would have to be pushing the opposite way that I suggested connecting (coming from the angle port towards the other two ports).

Next up: RoverStat when it arrives.

Ok, RoverStat arrived! Tested it, could very likely work. The pressure relief in our scenario is irrelevant. The bypass port labelled above is spring loaded as shown, so you would need flow entering the unit from the right to press against the spring loaded bypass seal. The drawing above (at least for the unit I got) is not correct as the bypass seal is never open, your flow is limited to only the two bypass holes. Stone cold (which at the moment is sub zero here in Michigan) the bypass looks to be sealed. I need to poke around a little with a screwdriver to see for sure but it looks tight.

So at all times the heater core flow would be limited to whatever goes through the two bypass holes (which could be enlarged to be the same as the cross section of the heater core hoses if you wanted to maintain the same flow). When the thermostat gets hot enough, it opens and the majority of the flow would go to the radiator. The cooling system would be a pressure equalizing type deal, same as the factory config. Cold factory, the water pump pressurizes the head with the only possible outlet being via the heater core (and those tiny hoses at the thermo neck but I'm ignoring those for now). Same with this unit. Hot factory, the thermostat on the front of the head opens and the heatercore is one of two possible paths for the water, flow dictated by the capacity of each and the resulting backpressure I guess. Most of the water flows to the radiator and some leaves the back of the head to the heater core. Hot with this unit, the waterpump pressurizes the head, the only outlet being the back of the head. Rover thermostat when open, water can go either through the thermostat to the radiator or through the bypass holes to the heater core.

I can post up some pics or whatever anyone wants at the moment while the unit is loose. I'll draw up a new sketch and post it and you guys can tell me if it is stupid or the cheapest workable non-spacer with heater core option I think it might be. :)