Is the expansion tank too low????

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scottie
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Is the expansion tank too low????

Post by scottie »

Hi all,
My T25 (1988) camper which started life as a petrol and has now been converted (not by me) to 1.9d from a Seat Ibiza. It had been blowing rediator hoses and I had posted before about this. Turns out that it was probably air in the system, simple enough.
I thought I had it sorted after some sound advice and directions to the wiki about how to bleed the system. But the water level still seems to want to drop and the temperature light flashes even when cold.
Now, when the engine has been up to working temperature and then left to cool over night the water level drops and the l;ight flashes, but the funny thing is, when I take the top off the expansion tank the water level comes back to the top and I can't top it up any more???
So, i'm looking at the expansion tank and I see that if you were to fill it to the brim it would still not be high enough to completely fill the engine as the return hose is higher than the expansion tank.....with me so far??

In the Wiki it also says about a filler tank, but I have no filler tank?? Should I have one??

Should the expansion tank be higher than it is?? If so, is there a conversion kit??

Hoping you can help me here so that I can drive from Rochester (Kent) to Fort William (scotland) over THE next few days starting tomorrow!!!

Cheers,


Scottie
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Horza
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Post by Horza »

The fact that the tank seems to fill when the pressure is released shows there is still air in the system where you can't see it as you cant compress water.

The other tank behind the numberplate is a partial solution to this in that air/water can be forced out through the cap (black cap for a diesel, blue for petrol) and then as it cools water is sucked back in, sorta bleeds as it goes.

I believe all my pipes on my origional engine where below the top of the tank but given a sealed system this might not make any diference as with one hole the water wouldn't fall out unless air could get in.

I'm just thoerising but if it were me I would get a new black cap and a second hand overflow tank and a bit of pipe, put it together and bleed the whole thing again at least.
Euan

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scottie
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Post by scottie »

Sounds like a plan Horza.
The cap I have on it at the moment is blue and not black. What diference could this make?
What about the filler tank, is there a standard filler tank I could get from VW with fitment and a place to fix it on the can?

Cheers for the advice :o)
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Horza
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Post by Horza »

I'm told the pressure valve is set to a diferent pressure on the black cap, I don't know if its more or less though.

The pipe plugs onto the cap and runs down to the nearside of the hatch behind the numberplate. The tanks are all the same and you might get it from GSF, VW or JK. Just make sure they understand it's not the header tank but the overflow/filler tank from behind the hatch you need. There are screw holes in your rear valance (is that the right word?) to fit it to (open the hatch and you'll see them at the bottom).

It's a five minute job to fit and the diesel should bleed as it drives rather than these tricksy petrol thingers with their nose up in the air (TBH I didn't do the nose in the air thing with the 2.1 last time it was bled and it seems all good now) so you could pick one up from a variety of places and fit it on the way. Remember to let air out of the radiator.
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Post by Simon Baxter »

All caps are now blue, black ones generally don't hold pressure, well everyone I test at the garage is scrap.

Sounds head gaskety to me, best get it checked out properly.
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Horza
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Post by Horza »

Poo. :oops:

How do you test them Simon? Does that mean they are now all the same, no diesel/petrol diference?
Euan

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Simon Baxter
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Post by Simon Baxter »

With a cooling system pressure tester, test caps and cooling systems.

Pressure should be somewhere in the region of .8 to 1 bar.

pressurise water and it raises it's boiling point, so keeping coolant under a bar of pressure stops it boiling at 100°c.
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scottie
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Post by scottie »

Simon Baxter wrote:All caps are now blue, black ones generally don't hold pressure, well everyone I test at the garage is scrap.

Sounds head gaskety to me, best get it checked out properly.


Cheers Simon,
there is no water/steam present in the exhaust nor any signs of oil in the water either. However, I am still puzzled at how there can be air getting back into the hoses after they have been bled and show no signs of air in the pipes??

I can only think that the expansion tank is spitting out water when the van has been running for a while, then sucking in air when it cools. I might set up an experament with a squeezy bottle, double sided sticky tape and some sticky back plastic...in a true Blue Peter style, to see if I can catch any water.

Any other suggestions welcome.....

Scottie
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Post by Westy.Club.Joker »

Read the Wiki on system filling. If you run the engine up to 2000 revs (get a mate to sit in the cab and throttle it) and have the header tank cap off, the water level will be seen to drop to approx half the tabk level. Fill up now while the revs are held, and then cap it BEFORE dropping the revs again.

When it`s stopped and cold you may have quite a gap of air in the top or the header, mine is like this with no ill-effects, so I presume it`s OK. When it warms up the gap drops a bit and you can see the water circulating from the hoses, the top connection returns water to the header, so the bottom one (which is obviously submerged at the base of the tank) supplies the water to the engine/pump.
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scottie
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Post by scottie »

Thanks Westy,
I did the whole bleeding of the system thing and it did help, for a while. Then the problem has returned again and the low water level light has come on again, especially when cold a fter a good run.
I am going to try and get it pressure tested today as I don't want to get half way to Scotland and have trouble.

Scottie
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Horza
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Post by Horza »

Without the overflow tank on when the coolant cools it can suck air in through the cap rather than water like it's supposed to.

If your taking it round to a garage ask him to sniff the coolant for exhaust gasses just in case Simon's worst case scenario is on.
Euan

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scottie
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Post by scottie »

in the garage now.......fingers x'd
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Post by clartsonly »

just a silly thing, I assume you don't still have the bleed needle open or the screw loose in the front raidiator? and are you sure your cap or expansion tank water level thingy isn't leaking? I know both of mine started leaking when I had air stuck in the system.
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