Coolant Question?

[graeme1969]

Gday all. Can someone explain what is going on with the coolant in this pic. The engine had not been run for an hour or so but as soon as I fired her up there was a continuous flow from the pipe shown on the pic and the coolant level which appeared normal disappeared out of sight. The water temp was only Luke warm. With the engine not running the coolant level sits as though everything is sweet. Is this normal?

[MudRunnerTD]

Have you got any coolant in your overflow bottle?

Have you run your car till hot with the Heater switch On and the Fan On with the cap off? Do that, wait for the thermostat to open ( you will know) and top up with fresh coolant keeping it topped up the whole time. You might have an air lock or something. I have wrapped a little electrical tape around the bottom of a funnel for a snug fit into the radiator top and over fill it and bleed it out. You want the thermostat to cycle open/closed a couple of times and see how that goes mate

[graeme1969]

G'day MR,

The overflow bottle level hasn't changed in the last 6 months, and the coolant looks like new. I will give it a go tomorrow with your suggestion and see what happens.

Thanks.

[threedogs]

Cutting the bottom off a 2lt Coke bottle inverted in the
radiator is a snug fit, Helps to bleed if facing UPHILL too.
Is it Diesel or dual fuel ??

[batesy]

dont top up with coolant unless it's the same coolant just use water.

[happygu]

Graeme,

The coolant is pumped around the motor, in a never ending loop, and is designed to flow straight through the radiator to dissipate the heat, and back into the loop. In a perfect system, you wouldn't need the expansion tank, as it would just keep looping around.

The coolant itself reaching temperatures near boiling point, causing it to expand around approximately 3% - 4% of its volume, hence the overflow bottle to catch the excess returning fluid.

When the fluid in the cooling system heats up, it expands, causing the pressure to build up. The cap is the only place where this pressure can escape, so the setting of the spring on the cap determines the maximum pressure in the cooling system. When the pressure reaches around 15 psi, the pressure pushes the valve open, allowing coolant to escape from the cooling system. This coolant flows through the overflow tube into the bottom of the overflow tank. This arrangement keeps air out of the system. When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled.

You will always see the coolant level drop a little once the car is running and the thermostat is open, as the water pump is then dragging fluid through the system....

You may have just opened the radiator cap at a time where the coolant had cooled enough to be drawing back in from the overflow tank in combination with the thermostat being open ( most likely ), you may have a small airlock in the system or your radiator may have a blocked tube/core, causing a little more fluid to go to the expansion tank.

Mic

[Parksy]

Does that pipe connect to the top of the thermostat housing or expansion tank? If it's the thermostat housing, your thermostat is stuck open or missing completely.

Edit, looking at that pic closely, the pipe is fitted below both radiator cap seals suggesting it's from the thermostat housing.
Change your thermostat, then do as suggested above.

[nissannewby]

You should get flow through that pipe nearly always with the lid off even with a closed thermostat. It's just a bleed off line so whatever pressure is at the thermostat housing will go through there as well. It's normal.

If your vehicle takes a while to get to operating temp or stays really cool then it could be a thermostat issues.

[graeme1969]

Gday all.

It is a 91 GQ TD42. The pipe which is flowing is coming from the thermostat and the temp of the fluid is only just warm. I am thinking that there should be nothing coming out of that pipe unless it gets up to temp. Might be up for a new thermostat? Should I try bleeding it first or just go and get a new one? Sounds like a good excuse to have a play around in the shed.

[Parksy]

You should get flow through that pipe nearly always with the lid off even with a closed thermostat. It's just a bleed off line so whatever pressure is at the thermostat housing will go through there as well. It's normal.

If your vehicle takes a while to get to operating temp or stays really cool then it could be a thermostat issues.

Interested to know how coolant flows through a closed thermostat?