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Re: 04' Passat Overheating
appears we have an Air lock scenario and you will need to perform a
the vehicle on level ground, when cold remove coolant filler cap,
start engine and leave to idle, turn heater on full and blower to
max. When engine reaches operating temperature watch and listen near
coolant filler, keep clear as gurgling and hopefully a boil over
should occur. Top up with very warm coolant and wait as it may do it
for heat inside vehicle if warm replace coolant cap but keep an eye
on temperature gauge as the ~Air lock may have moved on from heater
matrix/core so proceedure needs to be carried out again from COLD.
persistent boil ups/over attention must made in the cylinder head
gasket area, or possibly water pump?
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If you have changed the water pump AND the radiator AND the thermostat and still have the problem then the hoses should be checked to be sure they are not collapsing, also make sure that the coolant is 50/50 water and coolant and the thermostat is installed right.
You say that the hoses have a lot of pressure and are extremely hot. That's telling me that the coolant is not circulating. I would recommend changing the thermostat first, since it's the cheapest and more likely to get worn out first. A thermostat opens once the coolant gets to a certain temperature and builds up pressure, allowing coolant to flow. Either that or the pump. Just to verify, is the fan working? Hope that helps.
There is no radiator cap on the Northstar engine. The only cap is on the surge tank (or expansion tank) and is pressurized.
So the answer is Yes, a faulty surge tank cap will result in the loss of coolant and therefore lead to overheating.
The most common overheating problem with the Northstar engine is a blocked purge line(small hose).The purge line is designed to purge air out of the cooling system. There is a small diameter hose coming from near the top of the coolant tank (not the cap) ,this is the purge line. With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating. If the hose is clear, check for blockage at the nipple on the tank.Or trace the hose back until you find the blockage. The hose goes in to the engine to a crossover and comes out the other side close to the thermostat housing,the blockage may be there.
If the vehicle is overheating there will be a build up of pressure in the cooling system and the coolant will push past the pressure relief valve in the coolant reservoir. If this is the case the cause of the overheating would need to be rectified. The cap itself could be at fault. They tend to become brittle with age and the threads break. Check to see if o-ring seal on cap is in position.If not replace cap, not expensive.
If car heats up quickly and overheats , the problem is the thermostat.
The thermostat stays closed and traps coolant in the engine untill it reaches about 185 degrees , than the thermostat opens and allows coolant to flow to the radiator where it is cooled by airflow. ( airflow while driving is usually sufficient ) while idling , or in slow trafic , the fan keeps air moving through the rad. The heater core is strictly for heat in the winter inside the car.
The thermostat is the most likely cause of the problem , and even if it was good before , the overheat / boil situation likely cooked it anyways.
I am assuming the water pump is still getting turned by a belt. No water circulation by pump would cause same symptom as bad thermostat.
Overflow and expansion bottles are designed several different ways on different cars , but the theory is that as the engine heats up and the coolant expands , it goes to the tank. Later , as engine cools down after being shut off , coolant contracts. Radiator is replenished by coolant returning from expansion bottle.
It is probably the problem. To make shure that need to change the gaskets, one of the symptoms use to be thet the temp rises when you are running at speed 50+ average, where is supposed that the car gets a lot of air due by the speed and nobody thinks that will be overheated.
did the electric fan on the radiator start up? if this dont start up, it can get the engine overheated , specily if the car run in hot weather , an when the car stay on idle . The other problem is the engine head , the head gasket can blow and you get the compresion presure in the water chanal .Try to se of the oil on engine is gray? If gray you must change head gasket.
Hoope this can help you