Coolant loss mystery

Pilchard

Member
My 1.4 diesel is losing coolant somehow.

It was serviced and topped up 11 days and 110 miles ago. Following the warning alarm today it took 0.85 litres to bring it to the max line.
The same happened 2000 before the service, and again just before the service, so I asked the garage to check. He had it on a pressure test while he did the service and he reported no pressure loss.
A bit of a mystery.

The temp-gauge is very lazy and never moves from its 60 degree start point unless on a long run... and then never hits the middle point where you'd expect it to be. There could be a connection... but maybe not. Either way... the lazy gauge is another mystery I've had in mind to look into.

There is no engine-bay staining visible from just casual inspection and, fortunately, there is no sign of oil contamination.

I did notice a little windscreen misting the other day, but assumed it was condensation from the water ingress I've been getting in the rear battery/underfloor area from the (I presume) vents behind the bumper.
Water-pump was done along with the cam-belt early last year.

So... can anyone advise on classic or well-known coolant loss locations?
 

Robin_Cox

Member
The temperature gauge thing suggests that the thermostat is failed or part-failed open so the coolant is constantly going through the radiator instead of staying in the block to warm up. Apart from that I don't have a clue - I am certain that someone much more knowledgeable will be along soon. I wonder though if that means that the coolant never usually hits a point where there is vapour pressure generated - perhaps some kind of leak that only occurs when there is enough pressure to cause seepage? Hope you are able to resolve this soon!

*addendum - if you have an ODB reader or access to VCDS, one thing worth checking would be both channels sent from the coolant temperature sensor (to the engine ECU and the dashboard needle respectively) - if these differ significantly, it could inform you whether the temperature reading is genuine or if there is instead a coolant sensor fault needing to be rectified (or both!).
 

PlasticMac

Member
If the pressure test was good, it points to the leak being something that gives way when hot, as the pressure test would have been cool or cold, I'd think.
Mac.
 

audifan

A2OC Donor
Replace the expansion tank cap and seals. Is there any signs of coolant down the sides of the expansion tank or around the overboard vent of the expansion tank?
 

ashley7715

Member
Check the expansion tank overflow and see of its been leaking from the pressure valve. I has an issue with head gasket failure when hot on a tdi AMF engine (early tdi's) All pressure tests were fine but possibly done when cold or it just didn't show up. After a lot of part swapping the head gasket fixed the issue.
 

gagge

Member
When I had problems with loss of coolant it turned out to be an faulty o-ring. It was the one that seals the pipe/hose to the bottom of the radiator close to the temperature sensor.
 

Pilchard

Member
WOW!
It's worth owning an A2 just to get the back-up this forum gives!

Robin Cox....
I would normally assume the same as you but I have a camper... 2001 Boxer 2.8HDI by Auto-Sleepers... that takes ages to get up to temp (heater and dash gauge) and had the stat replaced a couple of years back. It made no difference at all.
Re your addendum... if I have to look up the acronyms (ODB & VCDS) to find out what things are then it means I don't have them and wouldn't know how to use them anyway... but I do know where you are at. If a simple fix don't work, I'll pass your comments on to the guy at the garage I've just started using. I've sent him a text, but it's Easter, so......

Plastic Mac...
Yes, that's what I'd assume.
I had a diesel Avensis that, unknown to me, had a tiny leak on the rad which only lost significant coolant when I gave it a long high speed pasting one really hot day. The spray unfortunately was shorting the gauge sensor so the car didn't know it was running dry on coolant... and neither did I 'til my keen-nosed wife smelt something and I pulled over, switched off and got the bonnet up. Even then, I wondered why the engine wouldn't turn over. The AA man sussed it... the coolant loss had caused megga overheating and a nearly fatal partial seizure... which is why the good battery would not turn the engine. He patiently cooled the thing down and ran some K-seal into it. It eventually started, ran as if nothing untoward had happened, and the car was still performing perfectly 3 years later... same rad... when I sold it.

audifan...
I'm, of course, hoping it IS something as simple as a cap seals.
Now you happen to mention it, there was a little still wet red spillage around the flange that runs round the circumference of the expansion tank. There was also a little pink bead sitting in a little recess located above the horizontal flange at about 1 or 2-o-clock (looking down from the front). It that the pressure relief vent. The O-ring on the cap looks OK and feels like a good tight fit as it screws down, but that don't prove anything and a new cap is cheap thing to try, and may even be the solution... touch wood.

Dymtro
I reckon audifan is correct, but although I'm pretty sure they are dry, no harm re-checking.

audifan....
I hope you are right about the the cap. Always check the simple stuff first, eh?

ashley7715
You are making me depressed! I don't want to be depressed! I'm not listening..... Everyone else says it's the cap seal and gagge says it might be a radiator bottom pipe/hose o-ring.
The power of positive thinking. It WILL NOT be the head-gasket. it WILL NOT be the head-gasket. It WILL NOT be the head gasket. it MIGHT NOT be the head gasket. It's PROBABLY NOT the head gasket.... is it?
 

audifan

A2OC Donor
The cap not only has the o rings it also contains the pressure relief valve. This is what allows the coolant to escape from the over board drain. The little square slot near the seam of the upper and lower halves of the tank. The cap can become loose on its threads also. Cheap enough and lets face it probably been on there for ages anyway. Head gasket should show on the pressure / leak test you have already had.
 

VAG fool

Member
In my other VW life, I have had expansion caps crack behind/under the sealing ring, hidden from sight!
Worth checking on 20 year old plastic components, especially those with dissimilar plastics (ultrasonically?) welded together.

Blown head gasket sometimes shows up as one or two adjacent spark plugs going rusty.
 

VAG fool

Member
Pressure test cold is not the same as under load at operating temperature, but what do I know?
I've had enough old cars that had weird symptoms to know that you shouldn't rule anything out.
 

Pilchard

Member
Pressure test cold is not the same as under load at operating temperature, but what do I know?
I've had enough old cars that had weird symptoms to know that you shouldn't rule anything out.
I can only agree with you. A head gasket could be holding well enough until the block and head get up to temp and the coolant gets up to pressure. But what do I know? I don't know what an ODB or a VCDS is, but the idea of having to have the head gasket done is giving me the willies.

But... an update.
I got instructed to nip into town 4 miles away for pizzas and a bottle of fizz. I put on some fun tarmac-ripping speed on the way back, just to coax some leakage from the system.
It worked. The old newspaper I'd laid under the expansion tank was soaked. I threw it out and mopped away all the coolant that had re-appeared around the rim of the tank... and from that little square slot audifan referred to... and stayed and watched. Despite having cooled off a little, maybe ten minutes after switching off the motor, the level in the tank was still just about level with that little square slot and coolant was slowly beading up and weeping out down the tank. I wiped it clean and dry and watched again... same thing.

So... general consensus is I need a new cap. Lets hope the majority are correct, because otherwise... it don't bear thinking about. The last head gasket I ever did was on an Austin A30, and they idea of paying out a grand to do the job on a car clocking 170k that cost me £600, don't fill me with eager anticipation.

Have just ordered a cap from Amazon. £3.49 for the cap and £4.99 delivery. No wonder Bezos is so bloody rich!
 

Skipton01

Admin Team
I had a similar issue on Tank a few years back - topping up the coolant once a week or so.

Having tried new coolant bottle and cap, with no success, my mind turned to the sinister things like head gaskets.

In the end, it turned out to be a leaky water pump which I discovered when I changed the cam belt. The tiny dripping was never seen under the car as it only happened when running and due to engine heat and the spinning of the belt, there was never any wet there, as water was flung onto a hot casing and evaporated immediately.


Fingers crossed a bottle and cap do it for you, but if not, check out the water pump area - take out the arch liner to gain access.
 

Pilchard

Member
I had a similar issue on Tank a few years back - topping up the coolant once a week or so.

Having tried new coolant bottle and cap, with no success, my mind turned to the sinister things like head gaskets.

In the end, it turned out to be a leaky water pump which I discovered when I changed the cam belt. The tiny dripping was never seen under the car as it only happened when running and due to engine heat and the spinning of the belt, there was never any wet there, as water was flung onto a hot casing and evaporated immediately.


Fingers crossed a bottle and cap do it for you, but if not, check out the water pump area - take out the arch liner to gain access.
Thanks for the input Skip, but the water-pump was done early last year along with the cam-belt, and only minimal milage since then.
 

Skipton01

Admin Team
Doesn't mean that it's not the culprit though. If there's been a freeze over winter, to prevent pressure build up, the weep hole on the pump can open up. Hopefully it's a less likely option though.
 

Proghound

Admin Team
Had something similar on my first TDI, which only showed up after I'd had the thermostat done. It would lose an expansion-tank full in about 200 miles. I gave it back to the garage and they found a slight crack in a plastic housing. I'm guessing that was the thermostat housing. They found it by leaving it to get stone cold overnight before looking for signs of dripping. Once the coolant circuit got towards normal temperature it was losing coolant as vapour.
 
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