Thread: 300TDI Coolant bleed pipe assembly

It's just a tee for the air bleed from the top of the radiator and t/stat housing, and there's nothing trick internally like a check valve either.

You can't buy the plastic do da by itself either, it's a complete hose assy, although they aren't very expensive.

Mine was leaking too (98 D1 tdi), replaced it with a three way brass barbed tee piece and hose clamps, haven't had a leak since.

Cheers

Goldey

I have Just replaced mine with a 3 way brass block and fittings to fit the hose diameters.( 300tdi) Prior to replacing the Plastic one the car was a bitch to bleed the air out. Found that one side of the plastic was blocked with dirt and gunge. Fitted it up and nil issues with air in the cooling system. Also I know a mate who cooked his motor when the plastic one sheared . Be careful driving and fix it asap. He noticed it when the car stopped, temp guage gave no warning of iminent doom.

Originally Posted by eddy

The Discovery has been losing a small amount of coolant over the last few months,have at last traced it to the 3way joiner in the coolant pipe[part no PCH117840]There is a slight weep from the plastic fitting.What is the purpose of this 3way filter/one way valve?
Can it be replaced with a 'T' piece?

The idea is that the three way union vents air away into the bottom of the header tank. It is supposed to prevent air-locks. By "air" we are talking about tiny amounts of gas that migrate through the cylinder head and head gasket. Even a few cubic centimetres per hour will eventually cause trouble if it is not vented away. Those small pipes can easily get blocked especially if radiator sealer is used. Good luck!

PS some early 3 way unions had a diaphragm valve but later ones don't have this. A 3 way union will do OK as long as the rubber pipes don't end up in the fan or fan belts.

OEM items have a one way valve in the line from the thermostat housing so that any bubbles are forced to bleed away from the top of the engine and into the tank, the shape of the unit (in theory) ensures that which ever side has the higher flow rate will draw fluid from the other inlet fitting and push it to the expansion tank.

while you can use just a normal t piece I prefer to replace the 3 hoses and use a Y piece so that the bottom 2 fitting come from the thermostat housing and the radiator and the basic flow is "uphill" into the expansion tank.

So.....it is not clear to me.
Is the oem part worth having?
I replaced mine with a brass t piece years ago.
But my low coolant sensor in the top drivers side of the rad (just below the hose there) sporadically bleeps at me and the solution is generally to bleed some air out of the adjacent hose.
Mine is a bugger to get the air out of and generally takes at least 2 or 3 top ups at the thermostat when cool until the alarm stops going off.
Does this indicate that the 3 piece fitting is not doing its job?

I understand it as this.....
There is a constant flow from the thermostat housing to the expansion tank. Any air in the block/head will be ejected to the expansion tank.
A venturi effect is created by this flow on the leg from the radiator, therefore sucking any air from the top of the rad and depositing it into the expansion tank.

Originally Posted by edddo

So.....it is not clear to me.
Is the oem part worth having?
I replaced mine with a brass t piece years ago.
But my low coolant sensor in the top drivers side of the rad (just below the hose there) sporadically bleeps at me and the solution is generally to bleed some air out of the adjacent hose.
Mine is a bugger to get the air out of and generally takes at least 2 or 3 top ups at the thermostat when cool until the alarm stops going off.
Does this indicate that the 3 piece fitting is not doing its job?

No the OEM part is not needed but when working it does help some engines. theres work arounds for it however.

if you're having air bleed issues with a t piece it means you have a blockage, the t piece is in just exactly the wrong position, or your thermostat is orientated incorrecctly.

usually

Originally Posted by jboot51

I understand it as this.....
There is a constant flow from the thermostat housing to the expansion tank. Any air in the block/head will be ejected to the expansion tank.
A venturi effect is created by this flow on the leg from the radiator, therefore sucking any air from the top of the rad and depositing it into the expansion tank.

thats pretty much it. with creative positioning of a T piece or a y fitting you can achieve the same basic result.

the very original pieces had a check valve in them to prevent flow back towards the thermostat housing, later ones an after market ones dont