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Matt, Engineer
Category: Australia Car
Satisfied Customers: 21711
Experience:  Automotive Engineer for 20 years, BEng hons degree,
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Where is the air relief plug on Nissan pulsar 2000

Customer Question

Where is the air relief plug on Nissan pulsar 2000
Submitted: 1 year ago.
Category: Australia Car
Customer: replied 1 year ago.
I've changed the coolant after flushing radiator and heater core changed the thermostat and still no heat and overheating
Customer: replied 1 year ago.
Sorry the question is what next to get the car running properly again
Expert:  Matt replied 1 year ago.


If you haven't already then do a reverse flush the cooling circuit (remove top hose to rad and use a hosepipe to push water into the engine until you get clear water out of the radiator hose) and top up with 30-50% fresh antifreeze. Also check that the small diameter bleed hoses that run from the top of the radiator and the top of the engine aren't blocked as this allow the air to vent back to the header tank automatically.

If you still have a problem then check that the water pump impeller / turbine isn't spinning on its shaft. You should be able to achieve this by removing the bottom hose from the engine and use a screwdriver or similar to feel for the water pump impeller blades, whilst your assistant turns the engine over by hand.

If you can stop the impeller with slight pressure from the screwdriver the pump needs replacing.

Also its possible the belt is slipping so its worth replacing its especially if the rubber ribs are cracked or it looks shiny on flat side of the belt - while its off check that the tensioner and other pulleys all spin freely the exception to this is the AC pump ( if fitted)

I'd also suggest ensuring that you've got all the air out of the system as this sort of episode can leave pockets of air trapped and prevent the coolant from circulating properly.

So check that the small hoses that run from the top of the engine and radiator that run back to the header / expansion tank are free flowing and not blocked

If these are OK then remove the tank pressure cap and run the engine from cold with the heater set to full hot

As the engine starts to warm, squeeze the large hoses running to the radiator to help displace any air - all the time keeping an eye on the level in the header tank, making sure it doesn't drop below the minimum and open any bleed screws built into the top cooling hoses - closing them off as soon as they start to gush water

Once the engine is up to temperature the tank should be quite full. Switch the engine off and leave it to cool

Then top up to the mark once its all cold and replace the cap

Customer: replied 1 year ago.
Have done all of that it's still overheating and still no heat
Expert:  Matt replied 1 year ago.


if the water pump is OK and all the pipes are flowing freely then the next step is to check that there's nothing in front of the radiator to impede incoming air and if the issue only occurs at low speed or in traffic then check that the cooling fan is coming on as it should by shorting out its relay

If this is all OK then its possible that you may need a new radiator

you can do a crude flow test by removing the rad from the vehicle, standing it on 1 end and then fill it with a hosepipe jammed into 1 end

you should get at least 8-10" of water height / head where its flowing out of the other pipe

if its just a trickle then replace the rad or have it re-cored

Customer: replied 1 year ago.
I had the radiator replace roughly six months ago
Customer: replied 1 year ago.
Also the air pump and cooling fan are switching on when required also no issue with fan belts etc
Expert:  Matt replied 1 year ago.



if the fan is working and its not using water and the water pump is flowing through all lines and the rad is new then I'd next use a thermal probe to confirm that the engine is really getting hot and you don't have a faulty temperature sensor

the rad water pipes should be about 90 to 95 deg C

Customer: replied 1 year ago.
Yeah I thought about that too but when the needle hits the red I pop the hood and check and the coolant in the reservoir is literally boiling and the the engine is hot, so it's definitely not a temperature sensor issue any other ideas
Expert:  Matt replied 1 year ago.

OK so if its genuine then its got to be a lack of flow

what would be worthwhile is to remove the thermostat entirely and run it without

as I've known new thermostats to be faulty on occasion

Customer: replied 1 year ago.
I will give that a try, would that affect the heater? As it still just blowing straight cold
Customer: replied 1 year ago.
How long do I run the car without, and I'm unsure if it will help cos it only over heats while driving not while idle even if I rev it
Expert:  Matt replied 1 year ago.


thanks for the extra information

if the heater is cold have a feel of the two pipes that run out of the engine and through the bulkhead as they should both be warm if not then there's an air lock or a lack of flow

or the heater matrix is clogged up and will need flushing directly with the hose

but you can drive the car for as long as wish with no thermostat

if it cures the overheating then you know it needs replacing

if it makes no difference I'd be considering a new water pump

Customer: replied 1 year ago.
Is the heater matrix the same as the heater core? As I flushed the heater core and it was pretty clean, also the top hose on the radiator is really hot and the lower one is cold? So it most probably Wil be air then can you confirm where the air relief screw is
Expert:  Matt replied 1 year ago.


yes matrix = core

I'd agree an airlock is likely

usually the air bleed screw is on the end of the radiator , at the top and there may another on the inlet manifold

this video should help

Expert:  Matt replied 1 year ago.


do you still need help?

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