Engine Cooling problem
1993 Volkswagen Jetta 4 cyl Front Wheel Drive Manual 170000 miles
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I had a overheating problem and already change water pump,thermostah,fan switch in radiator,and flushed the cooling sistem,fans start working but stil is overheating,a friend of mine toll me, about a air burble inside the head,how can i fixed? thank you.

Try bleeding the cooling system.

Always bleed air from cooling system after replacing coolant. Set heater for maximum heat. Remove radiator cap. Loosen drain plug and remove drain bolt (if equipped) from engine block. Drain coolant reservoir. Fill coolant reservoir to MAX mark with 50/50 water-coolant mixture. Loosen bleed bolt and fill radiator up to base of filler neck. Close bleed bolt when coolant flows out without bubbles. Tighten bleed bolt. With radiator cap removed, start and operate engine to normal operating temperature. Add coolant if necessary and check for leaks.