hello new user ....

I have a 2003 Astro RWD cargo work truck, it has 354,000 kms on it. I reside in southern Ontario Canada  I replaced the engine in April with a 2005 Blazer 4.3, it runs great but... ive had a problem since day one. 

it under cools..... every time I have replaced an engine it overheated on first start, this one didn't it undercooled and has ever since.

I put a new stat in , put new coolant in new heater hoses the works. it never heated up correctly. and still doesn't.  

heres the conditions today ... 

its 31 F today 

it heats up normally , there's plenty of heat from the heater over 100 F at the duct. 

the temp gage never go's up to the same level it did before the new engine. 

the ECT temp reading fully warmed up is 185 F via scan tool 

The temp gos up slightly if you turn the heater off , gos down slightly when turned to full heat 

it makes no difference if its a 80f day or 31  it doesn't over heat 

but ... the upper rad hose is cold  you can remove the cap with no problem there's no pressure you can squeeze the rad hose its not solid. 

I used a Fluke temp gage .... the heater hoses are 160 at the water pump  Rad 118 engine block at thermostat housing 125F

ive replaced the thermostat three times , 1  AC Delco   1 Stant   and motercraft the motercraft worked the best  All were 195 oem stats 

each time air bubbles came out when I loosened the thermostat housing 

ive tried everything I an think of to bleed it including jacking up the front passenger corner higher than the engine (the fill for the rad is on the passengers side ) air did come out but no change 

I'm thinking of putting a 180 stat in it with a jiggle pin to bleed air , but im not sure that will help 

any suggestions ?

Alex