Heater core ans spark plug / timing

,,,,the 1st question is,,,,,,,,,do you have the correct 2nd gen cooling system set up,,,,,

Yes. Its like that , but I have electric fan .  same radiator and same tank on the top, was redone 3-4 years ago but the last owner .

do you have the bellypan on it,,,,,,

The vented pan under the van ? Yes . I have it ! I just see in the repair manual that the thermostat original is a Harrison 195 deg . So , may be I have a 195 inside because it always at 195 except idle, down to 180-185 . If the last time the thermostat was changed , if replace by the original temp . May be a 180 will be better ? I never run the van on winter !

My question is : if I change plug from 45 to 43 ( cooler plug , and the recommandes plug by acdelco ) , I will see the temperature go down ? If temp go to 210 , 2 time when climbing hile , its not dangerous ?

plugs got not much to do with coolant temp,,,,,,the different heat ranges are for burning the gas,,,,,,,which depends on compression,,,,,oil burning,,,,how long your trips are,,,,,,gas octane,,,,,,,you want plugs that the tips dont foul out or melt,,,,,,,

220 is pretty common on our vans,,,,,,,over 250 will overheat it if you got the 50-50 coolant mixture and right radiator cap,,,,,,,,hotrodders use other types of coolant,,,,,,

Ok so, if run at 195 , and rarely at max 210, I don't have to be afraid ?

,,,,,and how accurate is the gauge you are using,,,,,,,,,200 degrees dont bother my van any,,,,,,do you have a fan on the water pump and a fan clutch,,,,,,what controls your electric fan?

Only one electric fan control by a thermostat in the core . On at about 185 and of at 180

I changed my thermostat this evening. For a 180. But it was a 180 . So !!!! Its not the problem ! Maybe the spark plug will do a little difference ! Maybe my electric fan is not enough ?