PRRT install and expansion tank connections

[fergus]

I have a Dry sumped 1.8 K series car (Caterham DS, with gold pump). I have no heater, so currently have a bypass hose from the water rail round the back of the engine to the current stat housing.

If I am planning on installing a PRRT, is there anything wrong with connecting the (bottom) expansion tank hose to the thermostat housing bypass inlet? I will remove the stat from the housing and replace it with the correct restrictor. The small bore take off from the inlet manifold to the top of the header tank will remain. I'll replace the current submarine with an ally tube. I'll also cap off the end of the water rail.

Thoughts? Can anyone forsee any problems with the above setup?

[Shaun_E]

If I understand your description, you will have no water flow through the block when the stat is closed. The water flows from the old thermostat housing, through the water pump and then the block, exiting the block at the water rail, flowing through the bypass hose and back to the thermostat housing. I would draw out the water flows before you make this change - I always have diffculty picturing it. I am fitting the QED remote thermostat shortly and will be keeping the bypass hose. An additional bypass is introduced with the QED kit going from the thermostat housing (in the radiator top hose) to the radiator bottom hose. I have bought a 2 outlet submarine from Caterham (it's for a Vauxhall car) that will allow the header tank and the thermostat bypass to connect to the bottom hose.

[fergus]

As part of the PRRT conversion the std stat is removed. This turns the stat housing into an external chamber if you like. When cold, the water flows from the pump, out through the water rail towards the top of the rad. However, there is then a bypass circuit built into the PRRT stat which allows water to then flow back to the current cold water feed into the old stat housing. When the stat opens, the bypass circuit shuts and all the flow goes through the rad.

My question really relates to a neat installation. Rather than cap off the current bypass inlet to the existing stat housing and also retain the sub pipe with the feed from the expansion tank, i was thinking i would connect the current bypass input to the stat housing to the bottom of the exp tank and use a straight piece of tube in place of the submarine pipe.

[Shaun_E]

I think I understand and it makes sense as, if you leave the existing bypass in place, there will be 2 bypasses! Where will you plumb the new PRRT bypass into? The QED install supplies a miniature submarine to go into the expansion tank lower feed. You need to plumb that somewhere so, if you do what you propose, I think you should plumb the PRRT bypass to the existing submarine and bin the supplied miniature one.
I've sketched the flow out: https://picasaweb.google.com/lh/photo/TJBJRYjDaqEx...
Let me know if I've understood correctly.