Coolant expansion tank completely empty.

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Gingermagic
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Coolant expansion tank completely empty.

Post by Gingermagic »

Hi All,

Last night, on a short trip, the temperature warning light was flashing at me for the whole journey.

I checked the coolant level, and all seems fine. So, I drove home with the light flashing the whole time again.

Today, after looking online, I've looked inside the coolant expansion tank. It's completely empty!

I'll go and buy some coolant now, to fill it up, but I assume that this is not supposed to happen. Should the main coolant tank fill up the expansion tank?

Could this be the sign of a bigger problem?
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Re: Coolant expansion tank completely empty.

Post by Gingermagic »

To clarify (in case I'm using the wrong terms), the coolant tank behind the licence plate is full.

The coolant tank in the engine compartment (behind the battery) is completely empty.

Also, I've read people suggesting simply refilling this tank with water rather than coolant. This may have just been for a 'testing phase'. Any thoughts on that?

Thanks,
Damian
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Re: Coolant expansion tank completely empty.

Post by TONYT25T25 »

Hello what model and engine do you have as this will assist with replies.  The expansion tank should be full, this is the one with the cap on top with tubes going in and out.  The refill tank is the one that is accessed behind the number plate and should be have a min and max mark on it, coolant should be half way between these two points but the tank should not be full.  The expansion tank is the one that alerts you via the red light if working ok.  If the filler tank is full it maybe that the expansion tank was unable to retrieve coolant from it due to a faulty cap.  Did the red light on your dash come on when starting the engine and then go off after starting. This diagram is an example, The text/note may not apply to you and is only an example of a problem.

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Re: Coolant expansion tank completely empty.

Post by TONYT25T25 »

Further to above there is information by MOCKI in the WIKI regarding this and maybe helpful. 
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Re: Coolant expansion tank completely empty.

Post by Mocki »

As I’ve said many times before ......Red flashing coolant light self tests when you switch the ignition on and then goes off ......
  
 The system is very simple....
 The headertank ( the one in the engine bay ) should always be full to the brim, and the top up tank ( behind the number plate flap) should be full to the max mark when cold. When the engine is up to normal running temp the coolant expands and is pushed into the top up tank, when the engine cools down the coolant is sucked back into the header tank
  
  
 The flashing red light in the temp gauge has two functions ....
 1. If the gauge is above 3/4 and it's flashing it means over heating 
 2. If the gauge is below 3/4 and it's flashing , it means low coolant in the header tank. 
  
 Check the pressure cap ( known as the Darlek cap on late vans , it’s a bayonet radiator type cap on early ).
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Re: Coolant expansion tank completely empty.

Post by Gingermagic »

Thanks for replying so quickly TONYT25T25 and Mocki,

Some more information based on yuor comments:

VW T25, 1985 model.

The engine is diesel.
I don't know much more about the engine than that other than it was replaced by the owner who had the van before us.

The light was on for the whole 15 min journey, both ways (not just on at the start).

The expansion tank is EMPTY. So empty that it almost looks like nothing has ever been in there.

The refil tank is filled to 'Max' with pink coolant.

If it adds to the picture at all, the heating system in the van seems to be completely broken. The controls seem to do nothing and sometimes hot air seems to be coming out, sometimes just 'air temperature'. The controllers do nothing.

What should I do, next?

I saw this comment, "Check the pressure cap ( known as the Darlek cap on late vans , it’s a bayonet radiator type cap on early ).", but don't really understand it. I don't know what a Darlek cap, or a bayonet radiator type cap is, or where to find them. And if I did, I wouldn't know how to check them.

Sorry if that sounds very dim. I'm more of a computer geek than an engine guy. Show me a faulty computer and I'll get to the bottom of it. With an engine, I'm back to basics with a lot to learn!

Cheers,
Damian
 
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Re: Coolant expansion tank completely empty.

Post by TONYT25T25 »

Hello, mine is a petrol engine so not familiar with diesel but suspect the cooling system is the same, the Dalek cap is the pressure cap on top of the expansion tank, called Dalek because of its shape.  This tank should be full to the brim, its operation is described in the thread posted by MOCKI.  I suspect the system after being checked for physical leaks will need bleeding. Again not a diesel owner so can only comment on petrol engines.  There will be more advice coming shortly I am sure from a diesel owner so you should be in good hands. 
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Re: Coolant expansion tank completely empty.

Post by 937carrera »

Mocki wrote: 20 Sep 2020, 17:33  
  
 The flashing red light in the temp gauge has two functions ....
 1. If the gauge is above 3/4 and it's flashing it means over heating
  2. If the gauge is below 3/4 and it's flashing , it means low coolant in the header tank. 
  
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Re: Coolant expansion tank completely empty.

Post by Mocki »

From your added description you have no coolant in the system in places , your description of the heater is classic air lock . Maybe just needs topping up and bleeding . 
you really should not be running the engine until you have solved this , because damage will or has happened 

Open the number plate flap , the tank you see there is the top up tank , it should be full to the max mark ( just below the level of the filler hole 

the other tank is the engine bay you can only see by taking the engine cover off is the header tank and will have a plastic pressure cap on the top of it , either blue or black twist off ( like a bottle top ) or if it’s older a metal bayonet cap like old cArs had on the top of the radiator, turn it half a turn and lift off 

the header tank should be full to the brim when the engine is cold . Never open it when the engine is hot or warm , it’s under pressure and will scald you 
fill it to the brim , just plain water will do you at this stage , you don’t need to worry about antifreeze until you know what’s going on 

a good picture of the full engine bay may help us help you . 
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Re: Coolant expansion tank completely empty.

Post by Gingermagic »

Thanks for the extra information.

Here are some photographs and an update.

The refill coolant tank (behind the licence plate) has, throughout this, been full, to a little way above the Max line, with pink coolant. Pretty much up to the lip of the opening.

Image 

I had to remove the pipe from the Darlek cap to open the coolant expansion tank.

When took the Darlek cap off, yesterday, I heard a fair bit of air pressure get released. I have no idea if this was air coming out as I opened the container, or air getting in. However, I guess that this is a good sign and means that there's no leak anywhere. 

Image

When I did this, yesterday, I heard a fair bit of air pressure get released. I have no idea if this was air coming out as I opened the container, or air getting in. However, I guess that this is a good sign and means that there's no leak anywhere.

Image 

This evening, I have filled the expansion tank, to the brim, with tap water.It took about 1.8 litres of water to do so. After replacing the Darlek cap and pipe, I started the engine.
The light flashed for a few seconds and then went off. Result! :-)

When I looked back in the engine compartment, it looked like the water level had gone down a little in the expansion tank. Just down to around the bottom of the neck that the Darlek cap screws onto.

This is definitely progress. I'm left with a few questions ...

1) Is it safe to drive the van like this?
2) If not, what should I be doing next?
3) Why did the coolant expansion tank not fill itself up from the refill tank?

Thanks again for all the help. This forum is amazing!

Cheers,
Damian
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Re: Coolant expansion tank completely empty.

Post by 937carrera »

Well, 1.8 litres is a lot of coolant to lose, where did it go ?.

Better that it's full, at least for now.

I would start by letting the van get up to temperature, probably by taking a 15 minute run, and then letting it go completely cold again.

Look at the water levels in both tanks before you switch off, and then again when it it stone cold.

Pressure when you release the dalek cap is not always a good thing, I'm sure Mocki will be along to give his expert advice before too long :)
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Re: Coolant expansion tank completely empty.

Post by Mocki »

Yes, fill it up , run the engine up to temp and have a good look round for leaks , make sure you switch the heater to hot , then let it cool and see what the levels are like .... I would expect the levels will be down a little , because you will almost certainly have air in the system , and that’s the next job, assuming you have either fixed the leaks, or didn’t have any ... bleeding it up . 
as it’s diesel it won’t take long , just take the cap off the header tank , have a gallon of water ready , and squeeze all the big pipes in the engine bay whilst keeping the header tank full ..... then start it up and run it up to temp , and follow the usual bleeding process 
from the wiki:TC:
 Bleeding the system on a diesel or GTI engined van is much easier. Fill the system as much as possible, then start the van, raise the revs to about 2K and top up the expansion tank while you have the revs elevated. Put the cap on and gently drive about half a mile. If the temp starts to climb over the mid-point on the gauge stop and re-fill with water. The half mile drive should open the thermostat. Now with the engine running crack off the radiator bleed at the front. Raise the revs to about 2K and allow it to bleed until no further air bubbles come out. Now switch off and top up as necessary on the main expansion tank. If you're suspicious repeat this bleed process again, but it shouldn't be necessary. Wait for everything to cool down and top up the tank behind the number plate.





 
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Re: Coolant expansion tank completely empty.

Post by Gingermagic »

Thanks 937carrera and Mocki,

Should I keep doing this with tap water (I added 1.8 litre of tap water today), or should I be taking some/all of the fluid out somehow and replacing with coolant?

Also, why didn't the coolant expansion tank fill itself up from the refill tank?

Thanks,
Damian
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Re: Coolant expansion tank completely empty.

Post by 937carrera »

It's fine with water until you complete the diagnosis, you can always replace the coolant with neat antifreeze later to top up the strength.

Not drawing back could be the dalek cap.... or something else, but stick to the simple diagnostics for now, no need to set hares running.
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Re: Coolant expansion tank completely empty.

Post by Mocki »

They won’t draw back if there is a massive airlock, air just cools and doesn’t really get much smaller , so the vacuum isn’t there in simple terms to suck the coolant back .... 
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