AIRLOCK IN COOLING SYSTEM

Hi Eric

This sounds to me like the cooling system has an airlock OR the 'stat has been put in backwards. Try running the engine for a short while with the rad cap tightened down to the first stop only and see if that allows the airlock condition to be alleviated.

Hope this helps you out.
-Steve

When you fill the radiator, did you make sure the car heater was set to Full Hot? If not, there could be an airlock in the water system. This can give the symptoms you describe.

disconnect the heat hoses going into fire wall , put hose into one with pressure and flush as it sounds like it could be bloked in the heater core,the other thing that could be the problem be the hot ,cold switch as it restricts the flow to makes the heater hoter or colder , it might need tlc or replacing as it is manaul not elec

That is normal, it will not get hot without the thermostat. The water cools in the radiator and falls to the bottom and the bottom hose is cold. This is what cools the engine and stops it from overheating.

Probably not water pump. Engine is notourious for vapour lock.
Cooling system must be blead of air before thermostat will work. Cool bottom rad hose is a dead give away. If you are still watching this forum reply , and I will walk you through the only way I know how to make it work properly. It's actually easy if you do it my way. I have worked on lots of cars , and this engine was the hardest to bleed out. Did one Yesterday , and works perfect.

remove thermostat and drill a small hole in it to allow the air to come up to header tank

You can flush the heater core. Or replace it. To flush it. You will have to remove the hoses that go into the heater core. Not from the heater core but from the other side. You point one of the hoses down to drain th coolant then run a strong stream of water through one of the hoses until it comes out the other. it usually says intake or outake near the hoses at the firewall. Put the hose into the hose using one of those spray ends for a regular hose. After you see the water coming out the other end, repeat the draining on the opposite hose. Reattach the hoses the way they were. Then refill your cooling system and bleed the system. Failure to do so could make one of the radiator hoses to burst. Always bleed your cooling system after adding coolant. Use the bleeding screw at the thermostat housing. Or use the radiator cap by slowly turning it until it starts hissing and all the air comes out. Don't take the cap off !! Just turn it slowly until only coolant is trying to come out into the reservoir.

dont get many faults with heater matrix in 51 plate golfs,but its a very common fault you have........the water pump impellor breaks up and dont move the water round the system,and the system is self bleeding..

Hi, I think you have an airlock in the pump,You need to drain the water totaly when stone cold.Drain radiator and disconect hoses from waterpump and top hose from themostat. Reconect pump hose and add water slowly into radiator through top hose untill rad is full then squeeze bottom hose vigourously,You ll feel the water tension in the hose, Connect all hoses and top up water level. This must be done cold as hot and cold water will cause an airlock. Hope this helps you out.All the best.Phil

You probably have airlock in the cooling system.

Not sure about the 4 runner's cooling system, but if there is airlock I usually take the coolant back out, take the thermostat back out, fill the engine block from this hole with 50/50 coolant, reinstall the thermostat, upper hose, fill the radiator and tank, then run the vehicle with the heater on max (rad cap off) and then fill the rad as the rest of the air comes out.