Bleeding the cooling system

 

1. Early 1.6 D "CS" engine has 2x 2 pin switches at the top of the rad, one switch does low speed, one switch does high speed.

 

2. Later, normal most popular style is the 3 pin switch which has one commin supply terminal then depending on the temperature depends on which terminal is made live to operate each speed on the fan.

 

The fan in both cases is shunt wound to achieve 2 speed operation.

 

Probably a leak.

best thing to do in that scenario would be to pressure test the system.

 

It's really not rocket science, honestly, and you really really don't need to jack any end of the van up, though, to me, logic says you would jack up the rear not the front! Water finds it's own level and all that, the radiator is the highest part of the system, so why would you jack the front of the van up and make the highest point even higher? surely thats making the problem worse, I never understood that bit me.

Why am I qualified to write this? Well, at the time of writing I have worked on these vehicles for 3 years professionally, I don't think there is a week goes by where I do not have some part of the cooling system in pieces and I have to bleed the cooling system. In those 3 years to press, I have never resorted to messing about with a jack. To me thats qualification enough that this system works, pending on you having a complete, sealed, pressure holding cooling system you can bleed it in 1/2 hour.

 

 

few bits of science you probably forgot from school.

 

You heat water, it expands.

You pressurise water, it raise it's boiling point.

You heat something in a confined space and you raise it's pressure.

You can compress a gas, you can't compress a fluid (much)

Water finds it's own level.

 

We're going to use these science bits to help us on the road to cooling nirvana.

 

 

Engine, the noisy thing in the back

Radiator, the big heavy thing at the front, 2 types, early 1.6D "CS" type with 2 switches towards the top, these are crap and if you even get the opertunity to upgrade to the later style please do. For some reason VW put the fan switches at the top of the radiator, if you have a leak and air is introduced into the system then coolant drops below the fan switches level, and they don't work! Well done VW for that one, clever boys.

Anyway, they soon realised the error of their ways and changed to a much better radiator, and they put the fan switch in a sensible location towards the bottom of the rad, much better.

The radiator, early CS or later style have a bleed screw at the top to let the air out, much like the ones on your radiators in the front room (unless your Welsh, but there are no 3 bar fires on a wedge!)

 

Header tank, the one INSIDE the engine bay, the one with the pressure cap, this must always be full right to the top, always, forever, period, fullstop.

 

 

Expansion tank, the one behind the flap (heh, he said flap) the level of this goes up and down with engine temp, only time to set the level of this is when the engine is clap cold as it is the only constant you can get, run it for 5 minutes and the level may have risen.

 

Thermostat, usually open about 87°c, it stops coolant flowing to the radiator when the engine is cold to let the engine warm up quicker, once it reaches a preset temp it gradually starts to open and lets coolant flow to the radiator to cool it down.

 

Fan switch, turns the dirty great fan behind the radiator on at a set temperature, usually comes on at 87°c and goes off around 76°c the thermostat and fan switch do a really good job of keeping the temperature of the engine regulated, thermostat opens, coolant goes to the front, rad temp reaches 87°c, fan comes on, cools coolant, temp goes down, , thermostat closes a bit, fan goes off, engine warms, thermostat opens more,fan comes on, la di da etc, you get the picture.

 

Heater circuit, is like a minature cooling system, it has pipes, a radiator (heater matrix) and temperature for the heater is controlled by a remotley controlled valve (much like a tap)

 

 

 

 

Lets presume you have a totally empty cooling system, say, you have changed the front to rear coolant pipes.

The T3 cooling system takes somewhere in the region of 16 litres of coolant, so for a 50/50 mix you need 8 litres of antifreeze.

 

First off, if you are filling a completely empty system, undo the bleed screw on the radiator, like we said earlier water finds it's own level, if you don't the job will take longer and you will use more fuel!

make sure heater controls for front and rear heater if fitted are in the hot position.

So, pour in neat antifreeze first until you can't get anymore in.

Close the bleed screw.

Fit header tank cap.

Start engine.

Remove cap, now pour as much coolant in as you can.

Once you can't get anymore in, rev the engine to 2000rpm ish.

The coolant level will drop, add more coolant till you can't get anymore in.

Keep revving, screw the cap back on, if you let go of the revs without the cap on and the level will swiftly rise and you will have just wasted a shit load of new antifreeze onto the floor, well done!

Okay, Got all your antifreeze in yet? You need to get that in first before you put any water in.

Go to the cab and give it a right good rev!, like a right good up to the redline rev!

Go to the radiator, undo the bleed screw and let some air out.

Go to the back, undo the header tank cap and add some more coolant, if the level has dropped a load, rev it to 2000 rpm again and get a load in till no more will go, cap on.

Go to cab, give it a rev, go to rad, let some air out.

Once you get to a piont where it feels like you can't get much more coolant in, then go to the cab and have a break, sit down for a minute and keep it revving at 2000 rpm to get it to warm up quicker.

To make it look like you really know what you are doing, flick the heater on and see if the heaters are starting to blow warm, for a real manly "I'm a mechanic me" look, set the heaters to demist and hold your hand above the vents, works great and if the missus is watching you may even get a brew out of that one.

If the heaters aren't even tepid yet, rev the nads off it again.

The heater circuit isn't controlled by the thermostat, so the heaters work regardless of thermostat position.

Once the temp gauge starts getting towards 1/2 way best let some more air out so let it idle.

Go check water level.

Top up as needed.

About this time I like to fill the expansion tank up right to the brim and attach the pipe from the header tank to the expansion tank cap.

Give it a rev, let some air out.

 

Now, listen to this bit, it's kinda fundamental as to how the system works.

The cooling system is meant to run at about 1 bar of pressure, thats about 15PSI in old money, that means that the coolant won't boil until about 115°c

So, the header tank is full to the brim, the cooling system reaches 1 bar and a valve opens in the cap and lets the excess pressurised coolant out into the expansion tank, the level in the one behind the flap rises.

once the engine cools, the coolant cools and contracts, if the system were to be totally sealed you would get rubber hoses collapsing, so inside the header tank cap is a second valve, a vacuum valve, this opens at some pressure or other (dunno that) and lets coolant from the expansion tank back into the header tank.

This keeps the header tank constantly topped up with coolant and no air in the system.

Right...

back to bleeding..

 

What we are doing here is warming the cooling system to increase it's pressure, we are using this pressure to expell the air trapped at the highest point by letting it out of the bleed screw.

easy really when you think about it.

When did you ever see your plumber with a acro prop under your house jacking it up so he could bleed the radiators?

You didn't thats why, so why should you do it on your van?

 

Right.

Where is the temp gauge? as we mentioned before, the thermostat and fan do a really good job of keeping the engine temps stable, from new the gauge should come up to half and stay there more or less, just over half fan should come on, just below half and the thermostat will start to close and bring the temp back up.

If at any point the needle goes over 3/4's you may have a problem.

 

Always run the engine up to test the cooling fan works.

 

With the engine running, cap on and pip to the expansion tank connected, i find it helpful to unscrew the cap with the pipe connected to let the last bits of air out.

 

Go for a good run

 

Come back.

 

Let some more air out of the rad, once it runs warm water with no bubbles it's done.

 

let it cool, check level when clap cold in the expansion tank.

 

If this doesn't work you are either stupid and havn't listened to the above or you have problems, possibly head gasket problems.

 

okay, pick that lot to bits then!!