1.8 tdci yet another heater/coolant issue

[Kevwrightuk]

So, having had quite a few peaceful months of motoring after much work, suddenly the heater decides to start blowing cool. 
Driving back from Edinburgh at night, I noticed the heater started to blow cold. 
The temp gauge starts to fluctuate between normal ( vertical) and 60 degrees. 
The temp indicator appears to be inversely proportional to the heater temperature. So when the gauge moves from vertical back towards <60, (when coasting down a big hill)  the heat increases slightly (perhaps when the thermostat closes) and then as it rises ( as I start working the engine) the heater goes cool again. 
lifting the bonnet reveals that the coolant is being forced out of the expansion tank and the rubber pipes are rock hard. Clearly too much pressure. 
 

A reminder of what has been done and what I have done to try and diagnose….

New head gasket and I have confirmed via chemical reaction test that there is no combustion gas getting into coolant. 
New expansion cap. 
No leaks to be found anywhere on system. 
Both breather/return pipes (6mm to top of expansion) free from obstructions. 
Coolant drained, radiator/engine block/heater matrix all reverse power flushed. No obstructions and water flows freely everywhere. 
New thermostat removed and tested for good measure. Opens and shuts as expected. 
New water pump which is doing its job fine. 
 

So I have to assume it is drawing air in from somewhere in order to create so much pressure. From where??? Haven’t a clue. 
I can’t think of another explanation so if anyone can suggest a check I’ve missed, I’d be eternally grateful. 
 

I am at the point of paying Ford to diagnose at a cost of £120 but have a horrible feeling they’ll just repeat everything I’ve done and say ‘sorry, can’t find a fault’. 
 

Surely once up to temperature, the gauge should stay pretty much at the 6 o’clock position even when the thermostat opens and closes?
 

Totally baffled by this.  

[Tdci-Peter]

1 hour ago, Kevwrightuk said:

Lifting the bonnet reveals that the coolant is being forced out of the expansion tank and the rubber pipes are rock hard. Clearly too much pressure. 
 

A reminder of what has been done and what I have done to try and diagnose….

New head gasket and I have confirmed via chemical reaction test that there is no combustion gas getting into coolant. 

A leak in the EGR cooler is a possibility. The gas in this is roughly at inlet manifold pressure (or a bit more), and rises with the turbo to about 2.4 Bar (35 PSI) gauge. So when the engine is working hard (Full boost pressure), gas can be forced into the coolant, while coasting will possibly allow coolant loss into the exhaust, similar to a CH leak.

The chemical reaction test is normally for carbon monoxide (CO), and works well for petrol engines with stoichiometric fuel mix. It will work much less well for diesels with lean burn, which generate much less CO (a richer mixture is needed for much CO). White smoke or antifreeze smell in the exhaust are much better tests.

Most of the time after warm-up, my coolant remains at almost constant temperature, a bit over 80C, usually only rising a few degrees if working hard either in low gear (lower speed = less airflow), or on a very warm day. The temperature gauge does seem to cycle a little (mm or two at the needle tip), but this does not correlate well with my added on temperature indicator (0.1C resolution), so I ignore it.

[Kevwrightuk]

Thanks for the reply and suggestions. 
I probably should have added that there are no smells  from the exhaust and no smoke at all. 
Oh, and the EGR cooler is currently bypassed so that’s also ruled out. 

Logically, there has to be a leak somewhere for pressure to build up but there’s no obvious signs of either an external or internal leak.
🤔

[TomsFocus]

Have you changed the coolant tank or just the cap?  The tanks fail over time, getting tiny hairline cracks that allow air/coolant out, reducing the internal pressure.

If it now looks like a Tupperware you've had beans in, it needs replacing.

[Kevwrightuk]

31 minutes ago, TomsFocus said:

Have you changed the coolant tank or just the cap?  The tanks fail over time, getting tiny hairline cracks that allow air/coolant out, reducing the internal pressure.

If it now looks like a Tupperware you've had beans in, it needs replacing.

That is a really good suggestion. I did take it out and give it a thorough clean when I rebuilt the top end and had wondered if coolant was coming out of the pressure relief hole. Very hard to tell.  I’ll drain it down a bit and take the tank off and take a good look. 
Cheers. 

[Kevwrightuk]

2 hours ago, TomsFocus said:

Have you changed the coolant tank or just the cap?  The tanks fail over time, getting tiny hairline cracks that allow air/coolant out, reducing the internal pressure.

If it now looks like a Tupperware you've had beans in, it needs replacing.

So fairly confident that there are no cracks or leaks in the expansion vessel. 
But there is definitely air/gas getting in from somewhere. 
as you can see from the images, a steady stream of ‘something’ is making its way from the radiator top hose to the vessel. 
Now if this was combustion fumes, I would have expected my test fluid to change colour. 

[Kevwrightuk]

After running at 3000rpm for 10 mins and left to idle, the coolant is pretty much boiling and can’t be seen in the expansion vessel. This implies that the level of coolant is low and it is only visible in the vessel due to an abundance of air trapped, given that water doesn’t compress and there’s only so much bulging of rubber pipes to be had. 
Turn engine off and coolant level immediately rises back into the vessel and can be seen at the minimum marks. 
 

[TomsFocus]

If the coolant is disappearing & reappearing due to trapped air, that suggests that it just hasn't been bled properly at the moment. 

Bypassing the EGR cooler may have affected the water flow.  (Systems are finely balanced through design). 

 Having the system vacuum filled could help rule out a bleeding issue.

[Kevwrightuk]

25 minutes ago, TomsFocus said:

If the coolant is disappearing & reappearing due to trapped air, that suggests that it just hasn't been bled properly at the moment. 

Bypassing the EGR cooler may have affected the water flow.  (Systems are finely balanced through design). 

 Having the system vacuum filled could help rule out a bleeding issue.

Running with cap off and revving to 3000rpm results in coolant bubbling and spewing out of the reservoir. Left to idle and it settles back down to a lower level. 
Temp sitting at around 80 so it’s not boiling. 
I have a horrible feeling the CHG may have failed. 

[TomsFocus]

Not convinced it's a HGF myself.  But if you do want to test the cooling system for leaks, you can get a coolant pressure tester for that.  Place it on the reservoir, pump it up to a reasonable pressure, then leave it overnight.  If the pressure is still the same next day, no leaks.  Prices vary, but you may even be able to borrow one from a local garage.

[nicam49]

That's a gr8 idea! I've  seen it demonstrated on Wheeler Dealers by Ant.,but cldnt recall all the detail enough to explain it on here. 

[Kevwrightuk]

Sadly, I don’t think it’ll be necessary. Repeated co2 test at 3000rpm and before it shot coolant everywhere, fluid turned yellow in a flash. Not good!!

More likely to be a block crack. 

[Kevwrightuk]

So… in absolute desperation, I’ve tried what most purists would describe as the ultimate bad hack, the cardinal sin, the worst thing you can do to an engine. 
But with a 14 year old car with 145k on the clock, what did the have to lose??

I poured a bottle of Steel Seal into the coolant. 😬🤪

2.5k later, the car is running brilliantly, no overheating, no coolant loss, heater is great. It’s never run so well. 
Am I a bad person?

Will the forum readers forgive me? 
All I can say is that stuff has saved the day. I was so sceptical and a non- believer. 
Do I think my luck will hold? No. But for now, the car is running like a dream. 
 

 

 

[unofix]

On a 2008 car with intergalactic mileage, I'd say a reasonable fix 👍

[Tdci-Peter]

10 hours ago, Kevwrightuk said:

I poured a bottle of Steel Seal into the coolant. 😬🤪

2.5k later, the car is running brilliantly, no overheating, no coolant loss, heater is great. It’s never run so well. 
Am I a bad person?

No, definitely very sensible!

The CO (Carbon Monoxide) test does not work well on Diesels as the lean burn (far more air than needed just for combustion) naturally generates very little CO compared to the stoichiometric burn of a petrol engine. So the Diesel needs to be made to work quite hard to generate enough CO to make the fluid change colour.

I used K-Seal on my previous car (it was a Vauxhall, so I guess it serves me right!), and that fixed a small HG leak. These products are perfect if being used for their intended purpose of curing very small HG leaks on older cars, where the cost of a full repair is not justified.