Venture 2001 engine overheat problem

There is no hot air in the driver cab neither. When the temperature reached red zone, oil change signal came out. I have to stop and let it cool little bit couples of time, so that I can drive back home.

I knew this van has problem of the coolant leaking, so I tried to add leak stopper into the tank(I was wrong, it was supposed to be added into radiator directly) and also added some coolant. But the overheat still happened.

Next day I had my van towed to mechanic, and he added some coolant using below funnel. After the van run around 5 minute, overheat problem solved and the hot air came out to the driver cab.

http://www.princessauto.com/workshop/garage/lubrication-equipment/funnels/pans/8225880-spill-free%E2%84%A2-funnel

But the van was running OK in one day only, the second day the overheat problem happened again. When I opened the coolant tank cap, the coolant is full. I had to tow it to the same mechanic, he checked and found a gasket is leaking. So he opened the coolant entering hose and put the leak stopper (looks like soil). Then added coolant again running around 5 minutes. This time the overheat problem seems solved. But actually the van only ran well in two days. Now the overheat problem comes again (with no heat).

The fan can work when temperature is very high, but the radiator cap section is not hot.

Looks like the coolant can't enter the engine cooling section (as I can see the coolant tank is full).

What is the problem? Is it the head gasket problem or thermostat problem?

Thanks too much.

lnglng

Maybe a pocket of trapped air, I would find a second opinion/ mechanic.....IHMO.....

Sounds like LIM gaskets or head gaskets. If you don't find out what it is and stop overheating the engine you'll be looking at getting the heads reworked too. You need to find the leak and fix it.

Head gasket, your trick will seal the head gaskets only temporarily.