Bars leak is crap. Lesson learned.
Almost certainly the radiator. At speed nothing but the water pump and radiator assist engine cooling (and thermostat, but it does it without, so not the cause) and the water pump certainly hasn't failed (most can't, a leak is a seal failure) so without further information, radiator.
You cannot flush a radiator. To fully remove scale and corrosion you'd need something so aggressive it would eat the radiator itself. They can be rodded, but if the radiator is in this bad of shape, a new one for ~$150 is a far better option.
You don't mention year/make /model, if the engine is higher than the pressure cap, bleed any air out of the cooling system at the engine block.
Bars leaks is a temporary sealer for emergencies or minor leaks we can't pinpoint.
Water pump ought to have Ben replaced without using it.
However we may now have blocked waterways due to bars.. Eg rad fins, debris etc especially I ally if using no or low level antifreeze solution..
Assuming no air locks in system? Belt tension ok? We can try back flushing and do also flush heater matrix. Check hoses not collapsing ? ( internal restrictions) and after refilling idle few minutes no filler cap.( filler cap ought to be replaced anyway as cheap and can affect cooling values significantly)
Check flow to header tank..by revving couple of times. Do unsure and feed /air bleed pipes to header tank are clear and not blocked.
I would get a infra red thermometer and look for cold spots on your radiator if possible. Look for signs of flow thru the rad. Stop leak stuff can clog little passages as it was designed to do that. If when you have it overheating and you turn your heater on high and it goes down then it is the rad. Then again heater cores get clogged by stop leak stuff also. Think of this as the side effect of the quick fix.
You need to drain, flush and CLEAN the cooling system with one part powered acid cooling system cleaner to get the Bars Leak, corrosion, rust and slime out of the cooling system.
NEVER drive a car without a functioning thermostat!
Check the coolant level & add if needed . You never said what kinda truck you have ..... . I would change that thermostat right quick tho .
pluged radiator.
So I had a leak in my coolant system, used bars stop leak on it. Most of it bled out of the water pump which was what was causing the leak.
Anyways everything was fine for months after changing the water pump. Then it started overheating at idle. I had the fan clutch replaced. Now it does fine at low rpms and overheats on the highway, even without the thermostat in it.
Any thoughts please
