so 20 min of cam brake in and no temp gain (tested mechanical gauge prior to running). was thinking maybe runnin on hose could be part of it..took to water and same ran it for around 15-20min in gear varying rpm idle to 3000 and still nothin on gauge (starts at 130 has 190 themostat) intake manifold water passage area is goo and warm heads nice and warm exhaust manifolds good and warm but not to hot..hoses from thermostat housing to circ pump is warm and lines from stat housing to exhaust stay cold. goin to swap stats again but feel like i should be seeing some temp gain in 20 min of running with a load. anyone else had issues with water maybe bypassing stat a lil or? in a hardin marine mercury replacement polished housing.?

Which thermostat housing?

190 stat? why so high?

190 is what engine builder wants.

Thanks
Also do not see a 190 stat, but what motor?
Assuming raw water cooled, so what pump (standard, 2 stage, other)?

How about a pic of the motor?

Did you use the Merc type tstat housing gasket that grounds the tstat housing to the intake manifold ? If yes, did you use rtv which blocked the gasket rivets from making contact to ground the two ? Did you paint the intake manifold including the tstat housing mounting surface of intake manifold ? If so, this can block the ground needed for coolant temp sensor to work.

BTW: OE marine engines use 140f tstats predominantly. 160f for many others - typically fuel injected. Nothing higher.

It’s a gen 6 427 tall deck made into 502 stroker. 4.250 crank, long rods,.070 bore etc.

temp gauge is mechanical gauge mounted in intake manifold next to stat housing. No rtv
raw water cooled. Hardin marine stainless water pump sis gel stage

Like you, I don't see why its not heating up. Temp probe in the intake or the Thermostat housing would be the same.

Wonder if there is something wrong with the new housing?

Your pump goes to the T-housing first, then is distributed to the manifolds, etc. Is there enough "pressure" from the pump to force open the T-stat and dump fresh cold water into the engine (backwards) Just spit-balling here?

Or visa-versa, putting enough water pressure in block to push open the T-stat. (rethought it--hard to push open a one way door)

If the Stat was in backwards the spring would not heat up, and never open. There isn't enough pressure to open it otherwise
Take any Stat and try a push it open by hand, it takes some pressure