I replaced thermostat, waterpump, coolant temp sensor ,flushed system, I get heat alot of it . no leaks what so ever I'm at a loss the van heats um past 260 in 3 mins but radiator doesn't boil over I can release the cap even! Please help whats next

 

First, did you have this issue before you did the work? Does the temp drop with the heater on? Did you bleed the air out of the system? Can you feel circulation from the engine back to the radiator? Is the radiator open to the road, in other words air flow not restricted to it?

 

replace the rad cap. The system needs to be pressurized. If the cap leaks, coolant vaporizes and vapor doesn't cool.

Also the vortec 4.3 eats intake gaskets like crazy. What a terrible idea it was to put those in full size vans. No wonder the v6 was phased out.

 

I think these still use a separate sensor each for the dash gauge and the computer. When the sensor on top of the motor fails it tends to read cold, mine thought it was -68'F when I put a scan tool on it to check. The dash gauge read the same as it always did before and after.

I would borrow a scanner with live data capability from somewhere or buy one from Harbor Freight and see what it tells you. If it's not boiling over it's probably not that hot.

But you could have an air pocket in there, as the coolant warms you get steam and that will make it read crazy things.