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Bleeding Heater

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If I have cause to drain my water system, I always have a mare getting the heater bled through again.

I've got a 3.9 EFi engine inserted. Heater pipes come off the front of the engine manifold/water pump, run along the even bank (Left as you look at the engine from front of bay), round the back of the engine and up to the heater matrix.



The hose off the back of the water pump pulls when I take the hose off the heater matrix. (Stick thumb over the end, rev and feel the the suction.)

The hose that feeds off the inlet manifold is always pushing hot water by convection and is very hot all the way to the matrix. The return from the matrix is always cold....

If I force water round by tap and water hose in the bleed / feed opening on the system above the even bank, pinching the hose from the manifold, I can push water round the matrix and system to overflow the expansion tank. Generally after this it all works fine and I have a lovely warm car.

Doing it this way is a total waste of antifreeze and relies on having tap pressure to hand.

I'm presently away from a hose and had to drain the water for a cam change..... How do others get past this little problem...

Please share your techniques...

Thanks in advance.


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Here is how I do mine…………

Remove expansion tank cap…………remove brass plug on Rad ………Remove the brass plug on the bleed tower shown …………….

Slowly fill the rad with a 50/50 mix until it is full ……………. Carefully and slowly squeeze the top and bottom hoses a few times to expel any air (acts like a pump).

Top up rad and refit brass plug …………………… then top up system from the bleed plug as in your picture above ………….. you will see the level rising in the expansion tank. Refit plug, make sure heater is set to hot and run the engine up to operating temp (i.e. thermostat open)…………… then top up the expansion tank once the engine has cooled………………. Job done………….

Usually V8 defenders are quite warm anyway, due to the underfloor heating from the exhaust and the heat from the engine that is blown back towards the bulkhead ................... truck cabs are very toasty ..............



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Tried your method Ian and didn't get any heat through the matrix....

Also tried the following and got a part result....

I clamped the hose feeding from the inlet manifold. Undid the top up brass stopper.

I disconnected the flexible pipe on the return from the matrix just above the rocker cover and blocked the return feed with a spare piece of pipe. (Stop drain back into water pump or to stop air in pipework.)

I raised the loose return pipe from the matrix higher than the matrix and top up hole and poured a few litres of water through. It flowed freely so I'm assuming no physical blockage in matrix.

I capped off filler hole and quickly unblocked return pipe to water pump and re-connected feed back from matrix, aiming to lose as little water as possible.

Tightened all joints and ran up to temperature. (Taking clamp off other pipe)

All was well with hot water on both sides of matrix and heat through heater in the car. I then went for a run to put system under pressure.... Heat dissipated and heater ran cold. I checked the matrix pipes... One hot and one cold....

I'm guessing an air block has formed again. My matrix pipes are the highest part of my system, so obvious place to collect air pocket...

Any other suggestions?

Does it matter which side of matrix is feed or return ?


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Seems it was a mixture of poor flow in the matrix and system running too cool.......

Flushed the matrix through thoroughly and then swapped the 82 degree for an 88 degree stat.

Used Ian's top up method and it worked firts time. We think that while running the system ran so old and the water flow through the matrix so poor, it led to cold air in the heater... All toasty warm now.


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