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?
 

Pilchard

Member
The new expansion-tank cap arrived late yesterday and this morning I replaced it.
Comparing the two, I noticed that although the internal floating capsule in the old one rattled around slightly when shaken, the new one didn't; but that needn't mean anything more than the two caps having minor and inconsequential design/manufacturing tolerances.
When installing the new one I noticed that the level of the stone cold coolant had remained above the Max line overnight... just level with the little square drain slot.
Took it for a drive into town, spent an hour there, and gave it a bit of a blast on the 4 mile drive back... enough to warm the coolant up but not roaring hot. There HAD been a little bit of coolant loss... dumped via the drain slot, but not much as the level was still roughly around the Max line.
A mystery. So I've put an old newspaper under it in advance of a 25 mile each way trip out tomorrow or the next day, and I'll just have to wait and see what transpires.

I levered out the capsule from the old cap to investigate how it functions. It's just a simple spring-loaded plastic valve with 2 or 3 mm opening clearance which I can only assume is actuated by high pressure instead of high heat because, unlike a cylinder block thermostat, boiling water made no impact on it and it required the same very firm finger pressure to open the sprung valve regardless of whether it was hot or cold.
 

PlasticMac

Member
The new expansion-tank cap arrived late yesterday and this morning I replaced it.
Comparing the two, I noticed that although the internal floating capsule in the old one rattled around slightly when shaken, the new one didn't; but that needn't mean anything more than the two caps having minor and inconsequential design/manufacturing tolerances.
When installing the new one I noticed that the level of the stone cold coolant had remained above the Max line overnight... just level with the little square drain slot.
Took it for a drive into town, spent an hour there, and gave it a bit of a blast on the 4 mile drive back... enough to warm the coolant up but not roaring hot. There HAD been a little bit of coolant loss... dumped via the drain slot, but not much as the level was still roughly around the Max line.
A mystery. So I've put an old newspaper under it in advance of a 25 mile each way trip out tomorrow or the next day, and I'll just have to wait and see what transpires.

I levered out the capsule from the old cap to investigate how it functions. It's just a simple spring-loaded plastic valve with 2 or 3 mm opening clearance which I can only assume is actuated by high pressure instead of high heat because, unlike a cylinder block thermostat, boiling water made no impact on it and it required the same very firm finger pressure to open the sprung valve regardless of whether it was hot or cold.
Yes, it's a pressure relief valve. Opens if pressure exceeds whatever the normal running pressure is. The cooling system is a bit like a pressure cooker, the pressure keeps the coolant from boiling, at 90 or so, which it would at high altitudes. That's why you can't make a decent cuppa halfway up a mountain.
Mac.
 

Pilchard

Member
Yes, it's a pressure relief valve. Opens if pressure exceeds whatever the normal running pressure is. The cooling system is a bit like a pressure cooker, the pressure keeps the coolant from boiling, at 90 or so, which it would at high altitudes. That's why you can't make a decent cuppa halfway up a mountain.
Mac.
Y'now Mac..... I know this stuff, but can't understand why I sometimes go into Stupid Mode... and in public.
 

Pilchard

Member
Update.
Yesterday was the first longish journey out with the new cap. 25 miles there... 3 hour break... 25 miles back. Should have been a sufficient test.
Newspaper under the expansion tank and coolant level half-way between min and max.
I just checked and the coolant level hasn't changed, and newspaper is dry as a bone with no staining.
We might have cracked it.
I'll still keep an eagle eye on it though, but am very relieved that the prospect of a head-gasket change has now slipped below the horizon.
Thank you all for your interest and help.
 

Pilchard

Member
Hopefully after a few more miles with the new cap, all is now good?
It's an odd one.
I've been keeping a wad of dry folded newspaper under the expansion tank and have been taking regular peeks.
After replacing the cap, I started off with the coolant level at max. It lost a little initially, down to about midway between max & min, but I put that down to maybe the system finding its happy level.
Then, even after the previously mentioned 50 mile round trip, no coolant loss.
Now, after a couple of short shopping trips into town and back... 4 or 5 miles each way... the newspaper shows only a small spot of pink dampage but the level is currently at min.
So.... I dunno. Am keeping an eye on it and trying not to obsess.
NB. all levels recorded when cold.
 

Howey

Member
As a general rule egr coolers can leak and cause exhaust gases into the coolant which strongly resembles a head gasket failure!
(Think the ATL has a egr cooler but could be mistaken!)
If you problem persists i would get a sniff test done and maybe a thermostat and coolant temp sensor just to get things opperating correctly
 

Pilchard

Member
As a general rule egr coolers can leak and cause exhaust gases into the coolant which strongly resembles a head gasket failure!
(Think the ATL has a egr cooler but could be mistaken!)
If you problem persists i would get a sniff test done and maybe a thermostat and coolant temp sensor just to get things opperating correctly
Thanks for that Howey.
Assuming that the pressure test, recently carried out by my garage while it was being serviced, was properly done.... presumably done cold.... what are the chances that either the cooler or head gasket could blow into the coolant only when warmed up, but remain tight when cold?
I'll pass this info on to my garage as and when.
Excuse my ignorance, but what does ATL stand for? My 1.4 is the lower spec/lower power tdi.
 

audifan

A2OC Donor
So you are still getting marking on the paper under the expansion tank? Now need to see which of the three possible areas it is coming from. The overboard vent, the seam in the expansion tank or through the level sensor. If you can add something to catch fluid in the vent, wrapped around the seam and around the sensor. It may be a very small leak that only appears under certain conditions so may be hard to catch. You are more likely to have a fluid escape from the vent or seam and steam or fluid from the sensor. The fix for any / all these leak sources is a new expansion tank.
My guess would be leaking past / through the level sensor especially if there are no other obvious signs.
BTW you have an AMF engine not a BHC or ATL. That means you do not have a water cooled EGR valve.


The other place to check for a small water leak is around the temperature sensor. Right side of engine towards the back below the tandem pump.
 

Howey

Member
Thanks for that Howey.
Assuming that the pressure test, recently carried out by my garage while it was being serviced, was properly done.... presumably done cold.... what are the chances that either the cooler or head gasket could blow into the coolant only when warmed up, but remain tight when cold?
I'll pass this info on to my garage as and when.
Excuse my ignorance, but what does ATL stand for? My 1.4 is the lower spec/lower power tdi.
Audifan is spot on so no egr cooler to worry about

If it was mine i would be looking to see if the cooling system is over pressuring. A stationary fast idle test should shed light on this. Say holding the revs at around 1500 rpm for 20 mins (using a well placed pole between seat and throttle pedal) whilst observing any unfolding issues. Heads and Head gaskets failures can behave oddly. Always use extream caution if you go to unsrew the pressure cap whilst coolant still hot!!
 

Pilchard

Member
So you are still getting marking on the paper under the expansion tank? Now need to see which of the three possible areas it is coming from. The overboard vent, the seam in the expansion tank or through the level sensor. If you can add something to catch fluid in the vent, wrapped around the seam and around the sensor. It may be a very small leak that only appears under certain conditions so may be hard to catch. You are more likely to have a fluid escape from the vent or seam and steam or fluid from the sensor. The fix for any / all these leak sources is a new expansion tank.
My guess would be leaking past / through the level sensor especially if there are no other obvious signs.
BTW you have an AMF engine not a BHC or ATL. That means you do not have a water cooled EGR valve.


The other place to check for a small water leak is around the temperature sensor. Right side of engine towards the back below the tandem pump.
Thanks for that. Despite my automotive suss being well below current ultra-tech specs... more Moggy Thou, Mini & Triumph push-rod engines... I should be able to get my joiner's head and hands around those three potential sources on the expansion tank.
Assuming the vent to be the most likely culprit... having seen a pink bead of coolant twinkling in it, and a ring of pink around the top of the seam... I'm thinking a small wad of cotton-wool loosely taped over the vent should be a decent indicator. Maybe similar for the level sensor. If they show no results then the seam and/or hose connections might be suspect. But the fact that a wet pink ring :)-!) on the TOP of the seam is a common factor then my assumption might then be that the source is higher up.
I double-checked the log-book and Engine number is AMF 14B086.
 

Pilchard

Member
Audifan is spot on so no egr cooler to worry about

If it was mine i would be looking to see if the cooling system is over pressuring. A stationary fast idle test should shed light on this. Say holding the revs at around 1500 rpm for 20 mins (using a well placed pole between seat and throttle pedal) whilst observing any unfolding issues. Heads and Head gaskets failures can behave oddly. Always use extream caution if you go to unsrew the pressure cap whilst coolant still hot!!
Thanks Audifan. I'll try that too... after the other leak checks. It'll give the neighbours something to tut-tut about.
I did once in my innocent youth unscrew a hot cap. I'll never do it again.
 

audifan

A2OC Donor
The level sensor is above the seam at the rear. That is the one I would check next. If steam / vapor coming out it will either evaporate or condense and run down the expansion tank to the upper seam area. You could also put paper under the temp sensor to prove or disprove any leak there.
 

Pilchard

Member
Yes.... I agree. And will also check the temp sensor.... just in case.
The level sensor is above the seam at the rear. That is the one I would check next. If steam / vapor coming out it will either evaporate or condense and run down the expansion tank to the upper seam area. You could also put paper under the temp sensor to prove or disprove any leak there.And will also check the temp sensor on the engine
 

Pilchard

Member
So... yesterday... I taped two pads of cotton wool to the expansion tank. One over the overflow and one around the level sensor. I also put a fresh wad of newspaper under the tank, then drove 25 miles to a nearby town. After a couple of hours I drove the 25 miles back home. When I got home I lifted the bonnet and found there was not only copious pink staining of cotton-wool pads and newspaper, but the level that previously had been below minimum had risen to well above max. I touched nothing and left it to cool overnight expecting the level to drop as it cooled.
Today... the level had remained at the same level overnight... well above max.
I took a quick photo, then removed the pink-stained pads and newspaper. My intention was to conduct the fast-idle test recommended by Howey. I was expecting the level to drop to it's previous low level when I started it up (presuming there was something like an air lock going on in the system)... but it didn't. So after literally only a couple of minutes, before it had got even slightly warm, I switched off and started to slowly unlock the cap. Coolant came spurting out of the overflow, so locked it back on again.
I'm flummoxed.
Would a thermostat stuck shut cause this maybe?
If it was exhaust gases escaping via a cylinder head gasket, only after the engine has become hot and the head possibly warping and this was over-pressurising the system, would it stay over-pressured as it cooled overnight?
Can't get my head around it.
 

Pilchard

Member
Is your water pump working? Do you have a Webasto?
I'd be pretty miffed if the water-pump wasn't working as it was replaced when the cam-belt was done approx one year ago.
You've now got me wondering now how to test this.
In my Moggy Thou days you just took the rad-cap off, pulled the throttle arm on the SU carburettor, and watched the rusty water flow along the top of the rad.
Have I got a Webasto? Well, I believe I have. because theres a switch on the dash and a Webasto sticker under the bonnet.
Knowing not one thing how this works other than it's intended to assist cold-weather heating of the coolant, I had always assumed it'd be simply a 12 volt heater element suspended somewhere in the coolant... a bit like those mickey-mouse 12 volt things you could plug into the cig-lighter and enjoy a brew while wondering how to get the car started on the battery you've just flattened.
Does the Webasto also have a failure prone water-valve on it? How would I test this? Does it involve hitting it with a hammer?
 

audifan

A2OC Donor
Think of the Webasto as a mini boiler. It is diesel powered and when running sounds like a jet engine. It lives in the engine bay against the right wing and if you have it you can not miss it. Curious what the switch on the dash is as the Webasto works automatically but can be turned off by pressing the ECON button. Webastos output directly feeds hot water into the coolant system allowing rapid engine and cabin heat up. If there is an airlock in the cooling pipes around the Webasto that could be part of your problem there is a bleed point on one of the pipes on the Webasto and the other bleed is on the radiator top hose, so worth opening these bleeds on an unpressurised system to see if any trapped air is released before running the car with the cap off at say 2000 rpm for 10 minutes to hopefully release trapped air. If coolant is being blown out while doing this then stop immediately.

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Webasto heater.



Now the water pump...

Even when the thermostat is closed there is still the need for coolant to flow otherwise the system would burst. So this flow i believe returns to the expansion tank through that little upper hose that comes from the rear of the block. So in theory with the engine running there should be a flow of coolant coming back to the tank. Not saying it should be a torrent but a steady flow.
Water pumps have been known to fail and the plastic impeller fall off the shaft.


BTW if it makes you feel better then go ahead and hit it with a hammer, but I doubt you will fix anything. I await the results of the hammer!!
 
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