Find a repair shop near you with an exhaust sniffer (the kind like the smog test places use)

Ask them for a favor...let the van cool down a bit until you can open the expansion tank blue cap.

Start the engine, put the sniffer wand over the expansion tank opening.

If you have combustion gasses leaking into cooling system the hydrocarbon reading will shoot way up.

Then it's time for head reseal or better engine.