Club 80-90 Forums

I've been having an issue with my cooling system for at least 2 years but it's starting to get a bit worse so thought it best to try to put it to bed and would appreciate your help. We have just got back from a run over to France; I'll try to describe what I've been seeing.

It's a 1.6 TD JX engine and I'm starting from a 'clean system' (rad blasted out, new Darlek cap, fully bled, pressure reservoir brimmed and header tank full to the max level). After 3-4 hours running at motorway speeds the red light will flash, and I'll find that the header tank is now brimmed and the pressure reservoir below the 'low' level, hence the light. I can then 're-boot' (bleed the rad, drain coolant from header into pressure tank and everything is OK again. I'm not loosing coolant and I'm not overheating. If I stop after a couple of hours and check everything, the rad needs bleeding a bit and although the pressure reservoir appears to be low, as soon as I crack the cap open the level rises to full again. Whatever is happening air is getting into the system somehow.

I'm suspecting the head gasket but can't understand a couple of things, firstly why the whole thing is so gradual and why it has not deteriorated dramatically over a couple of years and 10,000 kms (I always thought that head gasket failure was accompanied by clouds of steam and oil in coolant). Secondly I can't work out why the coolant is working its way into the header tank - as the air is collecting at the top of the pressure tank surely this should bleed out once the cap reaches its opening pressure, not the coolant. I did do an coolant exhaust gas test (liquid one) last year which showed negative but I guess this could have changed.

Any ideas?

thanks

Andy

Hi,

Im not up to speed with T25 Diesels, However I have done a fair few head gasket failures in my time.
If I were you I would be having the system pressure checked first and go from their. Otherwise you will be throwing good money after bad at it.
With head gasket failures..you dont always get oil in the water or vice versa. They dont always pressure the system either. I did a vw polo a few months back and it had done none of the above but was had compression down on two cylinders...the head gasket had burnt through between the cylinders...you catch my drift..

Have the cooling system pressure tested and go from their. I suppose it could also be a lazy thermostat ???? I know these vans can be a pig to bleed and if its not done you will have all sorts of issues..

Glenn.

Where did you get the new cap from?

It was a genuine VW cap from Brickwerks.

With a pressure test, are you talking about pressurising the coolant system and doing a leakdown test or checking the pressure in each of the cylinders? if it's the first then i think that it could be ok as a couple of times I've let it stop, cool down overnight and then checked the level in the pressure reservoir. it was low but again, as soon as i cracked the cap open, there was a hiss of gas and the coolant level raised to normal as the gas escaped (system was still under pressure).

I had the same issue a couple of years back, eventually the head gasket "went".
At first I had a randomly flashing red light, then it became more or less routine until it became permanent.

There is, somewhere, a small "leak" in the gasket which is letting combustion gases into the cooling system.
This pressurises the cooling system and forces the coolant down thus causing the flashing light.

Mine eventually blew the one of the front to back pipes off at the join in the engine bay - which was not a good thing to happen as I was just entering the Elbe Tunnel by Hamburg.

It didn't end well and involved the Polizei and the ADAC.

Yep, first thing to do is take it to a reputable garage and get the coolant tank "sniff" tested for combustion gasses. If positive you know you have a head gasket problem. If negative at least you have the peace of mind to know it isn't and to go from there.

I'm also not overly familiar with the diesels but this does sound like a small leak of combustion gasses into the coolant.
Make sure whoever does your sniff test does it straight after a good run and they get the end of the tester into the header tank(not in the coolant tho )
I had the same thing with our petrol 1.9 where it would be fine below 55mph but pressurise above that .

Jas

Thanks all for the info, I'll try the sniff test from a good garage; the last thing I need is for it to fail at an an inconvenient moment...

If it were you, would you go down the route of replacing the gasket or just throw in an Elite recon lump? The engine seems ok but it's got 190,000 Kms on the clock. It would be sods law for another engine fault to develop after throwing the cost of a gasket replacement at it (what's the going rate for this by the way?)? I've had the van for a good 5 years and plan on keeping it for a good few years yet.

Thanks

Andy

Andy, I am not a Diesel expert but I do know that repairing a Diesel motor is a lot less daunting than a WBX !

Head gasket = pretty routine job, even a cracked head is not such a big deal as some of the WBX "issues" we come across.

It may be slower, but it's easier and often cheaper to fix when it goes wrong. Unless it is an old smoky rattle box I doubt a whole recon motor will be called for !

Anyway, until you have a result from a sniff test you won't know, it might be summat much less serious

have you got a rev counter?

what speed do you cruise at?

are you sure its not running warm?

can you be sure you have the correct gearbox so that the engine is not reving higer than it should at cruise speed?

OK, so just had it looked at; 'sniff' test proved negative but we cannot think of any other reason for this happening. The mechanic said that if i hadn't run through with him everything that had been checked so far, he would start off by replacing the thermostat but as the rad is getting hot I'm sure it's not that.

Anyway, have booked it in to have the head taken off so it can be pressure tested for cracks as that's what I think it must be.

Any other ideas before I start to spend lots of my hard earned?

p.s. have rev counter, cruise at 100-105kph, gearbox is standard AFAIK. Temp Gauge is steady in middle of LED.

lagerhead wrote:
OK, so just had it looked at; 'sniff' test proved negative

lagerhead wrote:
Anyway, have booked it in to have the head taken off so it can be pressure tested for cracks

[Anyway, have booked it in to have the head taken off so it can be pressure tested for cracks]
Bear in mind that if the crack testing isn't done with the head very hot that any cracks present may not open up!
Easy things first!replace the darlek cap,check for places where air could get in[heater valve etc].
Try driving at 80ks,so the head is at a lower temperature [so head cracks dont open up?]
Good luck.

You could be loosing pressure causing kettling, the resulting steam pocketing forces water out of the system/
I'd be tempted to remove and check the header tank for cracks or leaking sender and if no fault there, change the cap
(you didnt say how long ago it was fitted). I had the exact same symptoms on a toyota and found the plastic header tank to be cracked.
When it became hot the expansion was opening the crack and causing water loss and heat build (through lack of pressure) when climbing long hills
Get it hot and pressure test the system