SortaFlush

You sure the temp switch isn't giving you false readings?

Crcale

Tested with a DVOM.. and I applied ohms to it to simulate temperature and it worked fine...

beer guy

i know its stupid but have you checked water pump.

Crcale

Yah it's flowing a lot of coolant. It sucked the lower radiator hose until it was flat.

Crcale

any more ideas'

Fabrik8

What? Exactly what were you doing when that happened...?

Crcale

i had a burp funnel on the car and forced the throttle open with my hand and it sucked the lower radiator hose flat...

slammed

I know you dont want to hear this but, If your coolant system is gaining pressure. Its usually from a blown headgasket. I hope its something else but I figured I mention it.

TNGChris

I know you said you've checked the cap pressure,but maybe try a new cap.It's a cheap option.Possibly the spring is weak when it gets hot?I had very similar experience on my car years ago when I first turbo'd it,and the cap was the culprit.Once the cap collapses and you lose some system pressure,temp goes up very quickly.
If the cap is,in fact,fine then you have to be getting added pressure into the coolant system under boost.There are "sniffers" that can detect combustion fumes in the coolant,so it may be worth it to call around and find a shop that can do this procedure-maybe run it hard down the street and [carefully!!]pull the cap off and test it.I could see a leakdown test missing an under boost headgasket leak with it's relatively low pressure-it may only leak during the high cylinder pressure it sees under boost.

Also,I had no issues with the stock single core rad,making about the same power you are,although it seemed to be right on the verge of it's capacity(I did eventually go to an aluminum 2 row rad).Do you have the stock fan or a slim fan on it?A slim fan can have trouble controlling a sudden spike in temp without a full shroud like the stock fan has.

Chris

backtoarms

Block test.