overheating

[gblades]

Normally there is a hose at the bottom of the expansion tank which allows liquid to enter and when it cools it causes the liquid to be sucked back into the radiator. Sometimes there is a 2nd hose at the top which allows air/water to circulate and makes it easier to bleed the air out of the system.
If your hose connects through the top cap and the hose drops down inside the expansion tank then just loosen the lid. The idea is when you release the hose it allows air to enter the expansion tank at the top more easily so the water can then flow back into the system easier. Otherwise you squeese the hose and have to hold it in that position until the air stops coming out and then release it and leave it a while again so the water is sucked back in. Loosening the cap just allows it to happen a bit quicker.

 

[madder]

ok got it. Thanks!

 

[Burnerman]

A typical Japanese system.....the radiator is kept completely brim full.
When hot water expands, it lifts the cap valve on the rad cap and allows water to run into the expansion bottle.
The entry hose for this is long, and must be kept below the level of the coolant inside it.
When the rad cools, the water runs from the expansion bottle, back through another one way valve on the rad cap - allowing the rad to remain completely full.
Nissan are still using this method but as gblades says, there are alternative ways.
John

 

[madder]

A typical Japanese system.....the radiator is kept completely brim full.
When hot water expands, it lifts the cap valve on the rad cap and allows water to run into the expansion bottle.
The entry hose for this is long, and must be kept below the level of the coolant inside it.
When the rad cools, the water runs from the expansion bottle, back through another one way valve on the rad cap - allowing the rad to remain completely full.
Nissan are still using this method but as gblades says, there are alternative ways.
John

This description fits my car. The car itself should be almost cold now, so I may go out and take a look in a few minutes. I notice there is a small water/coolant stain on the ground right underneath where the expansion bottle is located? Anyway, if we're all in agreement, I'll go out, loosen the lid on the expansion bottle, make sure the rad itself is brim full, try to make sure that the expansion bottle has enough liquid but hopefully not too much but I'm unsure how to deal with it if it does have too much. Anyway, once I've checked all that, I will make sure the heater is on full blast, start the engine, squeeze the top and bottom rad hoses and hopefully this will cure the problem? Does that sound about right? Any idea how long I need to squeeze for and how many squeezes, in general!

 

[gblades]

Yes that should work. If you are clearing the air you should see it bubble up through the expansion tank or at least see the water level drop. When it stops dropping you are done.

 

[madder]

Right, so I checked the radiator, which needed to be topped up a little to bring it to the brim. I also topped up the expansion bottle to just under the full line marking. I made sure the heater was on full blast and the expansion tank lid wasn't closed but rather just leaning into the tank fluid and then I started the car. I squeezed the hoses c few times but there was very little give in them. Hard to tell if there was any or much bubbling at all in the expansion tank. There did seem to be a small bit but it could have been down to me moving the thing to try to see if there were bubbles! Seemed to not bubble after less than a minute anyway. Eventually the fan under the bonnet in front of the radiator came on as normal. At that point the car had been running for 15 minutes or so. No suggestion of overheating. Thermostat stayed normal. But I guess I won't know for sure until I drive it for an hour or so? Any thoughts?

 

[gblades]

As the radiator fan is coming on it sounds like it is working fine.
There are two main causes of overheating. One is due to water not circulating which can be air in the water pump (which was probably your problem) or a thermostat stuck closed.
The second is a problem I had once in my old bmw when the radiator cracked and although the water level in the radiator was low it circulated fine but the water level was below the radiator temperature sensor so in traffic jams it would overheat. Until I got it fixed I would have to swerve the car a bit when moving slowly to slosh the water over the sensor to get the fan to come on

 

[madder]

As the radiator fan is coming on it sounds like it is working fine.
There are two main causes of overheating. One is due to water not circulating which can be air in the water pump (which was probably your problem) or a thermostat stuck closed.
The second is a problem I had once in my old bmw when the radiator cracked and although the water level in the radiator was low it circulated fine but the water level was below the radiator temperature sensor so in traffic jams it would overheat. Until I got it fixed I would have to swerve the car a bit when moving slowly to slosh the water over the sensor to get the fan to come on

Brilliant!
Well, I'm heading out for a 45 minute drive now, so I should know more then. I just really wish I knew how much coolant/antifreeze is actually in the cooling system as opposed to plain old water. But hopefully for now, it'll be fine. I have to work in Northern Ireland this weekend, so I'll be driving up and back there on saturday. I guess I better make sure to have plenty of water and rescue tape with me!

 

[madder]

OK, took it out for an hour. Got a bit panicked when I was in the city centre and the thermostat started to rise slowly. When it got to about 80% still a little short of being in the red, I decided to put the heater on full blast to see if that would help it cool down. It did, the thermostat started to drop and then settled in the usual spot about half way. But on a scorching day like today, and the heat on, even directed onto the windscreen, it's very very hot in the car. After about 5 minutes of that, I put the temperature to cold but left it on full blast and a couple of minutes later the thermostat started to rise again, so I put it back to hot and it settled down again. Eventually after about 15 minutes of this, I turned the heat off and drove for a further 10 minutes but the thermostat stayed at centre. Could it be that I 'drove' the problem out, or is it likely that I'll have to lash the heat up again if I'm driving for more than half an hour?

 

[gblades]

You are probably getting a little air sucked into the system so I think it will be an issue until it is fixed properly.
Maybe at higher engine revs the pump can work better but if you get stuck in slow traffic you might have to put the heater on.
You might want to also try shorting out the temperature sensor on the radiator so it keeps the fan on all the time. That way it will help to keep the radiator temperature lower when in traffic instead of only coming on at about 80C and therefore improve the cooling when the water pump is not working as well.

 

[madder]

I was just out again for anther hour. Same problem. It works fine for 20 minutes, then the thermostat starts to rise and then I have to put the heater on to keep it controlled, thereby baking myself in the car? And I can't even set it to cold air. It only helps if I set it to hot.
Will it get to a point where the coolant will be properly spread and the pump no longer activates on longer trips for example, or will I have to drive with the heater on?

 

[gblades]

Were you in traffic at the time?
If you were it might not have the same problem on an open road.

Its not going to get better though as it probably sucking in air through the leaking hose.

 

[madder]

Were you in traffic at the time?
If you were it might not have the same problem on an open road.

Its not going to get better though as it probably sucking in air through the leaking hose.

I was in some traffic. It wasn't bumper to bumper and it moved reasonably well. I have the leak well sealed. There is silicon tape wrapped around the hose in several layers and it's bonded well. No sign of a leak now. So, I suppose there must still be some air in there. I don't understand why the pump needs the fan to activate it? And of course the fan needs the heater! It's difficult being in a moving oven!

 

[gblades]

The pump does not need the fan in order to work but if there is air in the system the pump is probably not able to work very well so there will be much reduced water flow.

Without the radiator fan being forced to be on the radiator temperature will get up to about 80C before the fan comes on automatically and with your reduced water flow through the pump this can cause the engine to overheat. By forcing the radiator fan to be on all the time then when you are in traffic the radiator water temperature will be lower meaning the temperature of the water entering the engine will be cooler. This helps the cooling.

 

[Burnerman]

Just idly wondering if there is a radiator core problem here.....does it get universally hot all over?
John