I don't normally post threads but thought this would be helpful later on to others.
My FL2 2.2 TD4 (160 BHP) has always suffered a slow coolant loss, but it's getting worse.

So over the Christmas break I'm going to see if I can solve the issue, which I hope will help others later on.

My symptoms are a slow coolant loss in local journeys, maybe a top up from min to max every 2 or 3 weeks, which is about 250 miles.
However on a hard run at motorway speeds, it'll loose coolant at a faster rate. For example we drove the 50 miles to Plymouth this morning, and got a low coolant warning when I started the engine to come home, so I topped it up.
I drove home a lot harder than the outward journey, as the weather was better, and the low coolant warning came on after 35 miles. On lifting the bonnet, it was clear that the coolant had been expelled from the pressure cap.

The coolant loss does seem to increased recently, at about the same time that I removed the EGR blank plate that was fitted before I go the vehicle.


So is this the reason I'm now loosing more coolant, or is this a red herring? I guess I can fit another blank plate to see if coolant loss reduces.
EGR coolers on these are known to fail and leak, so that could be the cause. As to why removing the EGR blank would increase coolant loss I can only guess at.

The other reason could be a failing HG.
The HG was only fitting last November, and has covered about 7k miles in that time.

What I do know is the coolant seems to be pressurised very quickly, even before running temperature is reached (normally a sign of HG failure), and driving the vehicle harder increases coolant loss, to the point where it's expelled from the pressure cap.

I'm suspecting that a leak in the EGR cooler could also cause pressure in the cooling system, as the exhaust gasses are at a higher pressure than the coolant.

I've not done a CO2 sniff test yet, or a UV dye test.

I do know there's no visible leaks other than staining around the pressure cap area when I push it.

Some historical information, the coolant loss was still evident before I replaced the cylinder head last November, but it seems to be worse now.

Any thoughts on this?

On my F1 V6 I had a similar issue. Eventually traced to a pin hole in the radiator. Hard hoses, loss of coolant etc.
Pressure build up caused by coolant trying to boil I guess. Temp gauge never went above normal.
Might be worth fitting a tyre valve to a spare cap. Pressurising and inspecting before you suspect the worst.

Hope it's a simple one.

Egr blanking may have helped contain the egr cooler leak. Above test might show it up.

One to consider ? To add to your workload !!

I had a spare couple of hours to start looking at the issue.
I noticed that the coolant had hardly dropped in the 20 miles I'd done since I last topped it up.
I did those 20 miles at a steady 65 using CC, which seems to minimise coolant loss.

I bought the engine up to temperature by letting it idle, with several bouts of 3k RPM.
I turned off the HVAC just to minimise heat loss.
It took about 20 minutes to come up to the point where the thermostat opened, pretty much bang on 90°C according to the live data.
While monitoring the live values, I paid special attention to the coolant temp, MAP value, intake temperature and EGU duty %.
What I found was that at light throttle, the EGR % was tiny, just a few %. However at higher throttle (power outputs) the EGR increased to 90% at times, which also showed an increase in intake temperature, proving that more exhaust gas was going into the inlet manifold.
MAP shows over 160 kPa, which is above the 145 kPa of the coolant pressure cap.

I also had a CO2 tester in the coolant tank to show up any CO2, but this was pretty inconclusive, possibly changing to a very slightly lighter blue, but it was so slight it's almost imperceptible.
At 90°C there was no pressure showing in the coolant tank, at least with the engine off load.

I've some thoughts on the cause or causes, but please come up with thoughts of your own.

First off, while the car is running, I can hear a hissing sound from the exhaust.
I'm thinking that this could be that the cat is partially blocked. My reasoning is, when the nut chewed the piston up, there was loads of missing metal which went somewhere, some of which I'm thinking it's stuck in the cat.
This would cause the exhaust to become pressurised more than it should, possibly excessively so.

Now this higher than normal exhaust pressure will put more pressure into the EGR cooler than it's designed to handle, possibly opening up a crack, allowing exhaust gasses into the coolant.

It's also possible that once the power is reduced again, the extra pressure in the cooling system is pushing coolant back into the EGR system, where it's burning off as steam. I have noticed the exhaust steaming in this cold weather when the engine is cold, but it does clear when the engine heats up.

Next I'm going to add some UV dye, but I've had to order some, so that will need to wait.
I'm also going to add 2 EGR blanking plates before and after the EGR system, so I can eliminate heat in the EGR cooler.

Have you thought about doping your coolant with UV dye to make the leak glow? £16 on eBay for a kit with a bottle of dye and a UV torch from Ring (so it's a decent make) and should make it easy to find the leak


https://www.ebay.co.uk/itm/283380903775

Jayridium said:

Have you thought about doping your coolant with UV dye to make the leak glow? £16 on eBay for a kit with a bottle of dye and a UV torch from Ring (so it's a decent make) and should make it easy to find the leak

https://www.ebay.co.uk/itm/283380903775

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Yes, I have the dye and a UV torch to make it fluorescent.

I do however want to blank the EGR to inlet pipe before adding the dye. I am thinking that doing this will allow me to see if any dye ends up in the exhaust from somewhere other than a leaking EGR cooler. Once I'm sure it's not due to a HG issue, I can order an EGR cooler, knowing that it's not a waste of time and money replacing it.

Having now received and checked a replacement second hand EGR valve and cooler assembly, today I thought it was about time I set about sorting the issue.
When I took the EGR valve to throttle body pipe off, I saw it had it condensed water on the walls. As the coolant was treated with a fluorescent dye, and this water was fluorescent, it proved it had come from the cooling system.

So I set about the long and awkward task of removing the EGR assembly, in-between downpours of hail.
I gave it 3 hours then decided to stop for the day, as it was cold and wet, and I didn't want to pull the fuel rail or the cam cover off before leaving it till next weekend.
So next weekend I'll continue and hopefully will get it sorted then.

So yesterday I changed the EGR cooler for a second hand replacement, as I was reluctant to spend best part of £400 on a new one, if it didn't solve the coolant loss and pressurisation I'm getting.
I also took the opportunity to blank the EGR take off at the exhaust manifold, which will prevent any exhaust gas from even reaching the cooler. I also blanked off the EGR pipe at the throttle body, so the EGR system is completely isolated from the intake or exhaust.


Today I took it for its first proper run to bring it up to temperature, as I needed to get an oil filter for the wife's VW Eos.

Rather worryingly I had a low coolant warning come up on the return journey.
I topped it back up, but I'm unsure as to whether it was just low because the thermostat had opened, or the issue isn't solved, and I've got more serious issues.

I'll monitor it over the coming weeks to see what happens.

Fingers crossed it was just not filled properly, and the problem is now sorted.

Have you pumped the coolant system up with air and watched the pressure remain stable (hopefully) ?
It means that you can pressure test without heat and finds a multitude of tiny leaks if they are present. I have an expansion cap fitted with a tyre valve for this purpose.

Hope it is sorted.
I thought the filter for the Eos was going to convert Petrol into Diesel

andyfreelandy said:

Have you pumped the coolant system up with air and watched the pressure remain stable (hopefully) ?

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Yes, it did loose pressure slowly, like 2 PSI a day, but at that low loss it's almost impossible to trace.
There was a small amount coolant visible in the EGR pipe at the throttle body (I previously added UV dye), which shows it's most likely coming from the EGR cooler, but possibly only when the EGR cooler is hot (due to expansion?), so I think changing the cooler was a good move, providing the replacement is leak free.

andyfreelandy said:

Hope it is sorted.

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So do I. The engine definitely seems to run smoother than it it did, which suggests it didn't like coolant in the combustion air.

andyfreelandy said:

I thought the filter for the Eos was going to convert Petrol into Diese

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That was last weekend. It's back on a diet of derv again.
It was however overdue an oil change, on time not miles, so I was being lazy and not getting on with it.
Unfortunately I bought the wrong filter (there are 2 for her year and engine type, typical VW, and the law of sod means I got the wrong one.

Well it's still suffering from coolant pressurisation, which isn't what I wanted to find out.
As the EGR is completely blanked, I can only assume it's the head gasket passing a tiny amount of combustion gas into the cooling system.

That's a bugger.
Can you compression test? Never done a diesel.

As it is a small amount gasket might only leak when hot?
Have you done a sniff test in header ?

andyfreelandy said:

That's a bugger.
Can you compression test?

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I've not done a compression test as the injectors need to be removed for that.
However all 4 cylinders drop the battery voltage a similar amount, so that says the compression is even across all cylinders.

andyfreelandy said:

As it is a small amount gasket might only leak when hot?

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It only seems to pressurise the coolant when under load.
Letting it run off load doesn't pressurise the system any more than it should.

andyfreelandy said:

Have you done a sniff test in header ?

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Yes. There's insufficient gas in the coolant to change the colour of the test fluid.

However when I got home from work I could see tiny bubbles in the coolant, which suggests combustion products are getting into the coolant.

Looking like I'll be changing the HG again.
I'm going to use an OE gasket next time, as the one I used last time wasn't OE.

Could you have a slightly warped cylinder head? Or top of block not as flat as it should be?

Rank Amatuer said:

Could you have a slightly warped cylinder head? Or top of block not as flat as it should be?

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The head came from an early DS with just 9k on the clock, so I'd like to think it was flat. I did put a straight edge across it, and didn't see any light shining under the straight edge.
I'd hope the block would be flat, it's a substantial chunk of cast iron.

I'm thinking this issue is either the HG I bought wasn't up to standard, or maybe the mating surfaces weren't spotless, or it could also be my torque wrench wasn't tightening the bolts as high as they should, as I found out later on that my torque wrench was under torque by some 20%.

Nodge68 said:

I'm thinking this issue is either the HG I bought wasn't up to standard, or maybe the mating surfaces weren't spotless, or it could also be my torque wrench wasn't tightening the bolts as high as they should, as I found out later on that my torque wrench was under torque by some 20%.

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20% ! That's pretty significant. Are the head bolts torqued up dry or lubed? (I don't know the answer)

Rank Amatuer said:

20% ! That's pretty significant. Are the head bolts torqued up dry or lubed? (I don't know the answer)

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Yes it is, especially with course bolt pitches.
The torque settings are:
1st stage - 20Nm.
2nd stage - 60Nm.
3rd stage - 220° rotation.
Now if my torque wrench was under by ~20%, the clamping force on the head would be much lower than it should have been, which could account for the gasket allowing combustion gasses to pass into the coolant.

The bolts are coated in tin I believe, so no lubrication should be applied.

Does 220° rotation mean what I think in means? Torque evenly stage 1 and 2 then rotate the bolts a further 220°?

Has the head ever been off before you got your hands on it? It's possible the bolts have been over-tightened, taking them beyond their elastic limit, in which case they would just continue to stretch and not provide the sealing / clamping force needed.

Rank Amatuer said:

Does 220° rotation mean what I think in means? Torque evenly stage 1 and 2 then rotate the bolts a further 220°?

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Spot on. I'm well versed with angular torque settings, so didn't mess that part up.

Rank Amatuer said:

Has the head ever been off before you got your hands on it? It's possible the bolts have been over-tightened, taking them beyond their elastic limit, in which case they would just continue to stretch and not provide the sealing / clamping force needed.

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The head came without bolts.
They're disposable after removal anyway, so it had a set of new bolts when I fitted the replacement head.

I'm thinking it may be a combination of insufficient clamping force, maybe coupled with a lower quality gasket.