Simon's new Xantia V6 and Leaf blog

[Mandrake]

Ok Chaps, I had a bit of a scare today.

Today I did a trip of 20 miles, some of it on motorway, no problems at all. Then stopped for a few hours.

Then another short trip of about 8 miles with a short section of 50mph motorway and a couple of miles of slow residential streets. Just as I was dropping someone off and the engine was idling I noticed a low "thrum" as if there was a truck nearby so I turned the engine off to be sure - turns out it was the fans on high speed that I could hear, which is unusual as they don't normally ever go to high speed. Started the engine again and noticed the coolant temperature reading was 95.

Normal reading is between 70-80, and if you push it it might go to 85 for a short time. However this was 95 and climbing after I'd just been driving casually at 30mph with a baby and two other passengers, and I have never seen it go above 90 in the 2 1/2 years I've had the car (even when I gave it plenty of stick) so of course I freaked out and shut it off for a minute.

I then gingerly loosened the pressure cap to let out the pressure to check the level as I haven't re-checked it again in the last few days since the Forte went in, and I was worried it might be low. It promptly started hissing like crazy and boiled over through the slightly open cap. There was a LOT of pressure there, not like what you'd normally see if you loosened the cap on a hot engine.

With the cap slightly loosened and hissing I could hear it continuing to boil for about a minute as some steam and water spurted out before it settled down, so it must have been well over 100 degrees. Once it stopped I removed the cap completely and found the level was perfectly normal. I started the engine to let it idle with the cap off and the temperature dropped back to normal within 1-2 minutes, and the fan went from fast back to slow. (So apparently the slow fan speed is working - failed slow fan speed had crossed my mind)

Without much else I could do I put the cap back on and carefully drove the 8 miles home including motorway watching the temperature gauge like a hawk and it seemed 100% OK - temperature was in the normal 70-80 range and through it all the engine felt fine to drive with the temperature gauge the only clue something was amiss. The over temperature warning light did not light - I think it was at least 10 degrees away from that lighting.

So what happened ?

The only thing I can think of is there was somehow an air lock in the system after adding the Forte - I did drain about 1 litre out and add the Forte and top up the coolant and I did not bleed it, however 1 litre is barely below the level of the bottle so I wouldn't have though it would result in an air lock ? Also the car has driven absolutely fine for the 4 days since then under similar driving conditions - so why would an air lock choose today to make itself known ?

If it was an air lock, would letting the cap off and letting it boil with the engine stopped have cleared out the air lock ? I'm going to try bleeding it tomorrow anyway to be sure.

Or am I looking at something more serious than an air lock ? I really hope that Forte hasn't clogged up something important.

[myglaren]

With the pressure cap off it would boil like mad - as you heard.
The boiling fluid would produce a lot of vapour and could cause additional airlocks so a thorough re-bleed is called for Simon.

[Mandrake]

With the pressure cap off it would boil like mad - as you heard.
The boiling fluid would produce a lot of vapour and could cause additional airlocks so a thorough re-bleed is called for Simon.

Yes I will definitely bleed it tomorrow.

The thing is it shouldn't be boiling with the cap loosened - it will only boil if its above 100 degrees and it does not get that hot under normal conditions. I've loosened the cap on a hot engine plenty of times before and at most you get a hiss as pressure is released but no boiling as the temperature will be under 97. So something caused it to get well over 100 degrees under fairly easy going driving conditions, and for the first time since I've had the car.

[myglaren]

Wouldn't like to speculate on that other than the possibility of a dud thermostat or buggered water pump.

[Zelandeth]

The gauge shows you the temp of the coolant - not the internal surfaces of the engine. Also, 100C is the boiling point of pure water - tap water will start to bubble well below that as impurities boil out. If the engine is running warm, bits of the head etc will be well over 100C and water will start to flash boil there once the pressure drops. That's one of the reasons modern cars need a sealed system, they rely on it as the coolant is so close to boiling point in normal use.

Bleed everything thoroughly and keep an eye on it I'd say. If it happens again first thing to do is slam the heater onto full heat and full fan. Firstly that should be able to knock a fair bit off the engine temp - secondly it will give you a good idea if the coolant is still flowing if the heater's hot - if it goes cold you know there's no circulation.

Forte should be fine - it's required by Valeo for the warranty on the new matrices they supply! Apparently many manufacturers of cars now have it added with the coolant from the factory as well...So I'd not be blaming it for anything.

[CitroJim]

Almost certainly a random air-lock... I've had the same happen on an Activa a couple of times now.

No real reason, just one of those things...

[Mandrake]

The gauge shows you the temp of the coolant - not the internal surfaces of the engine. Also, 100C is the boiling point of pure water - tap water will start to bubble well below that as impurities boil out. If the engine is running warm, bits of the head etc will be well over 100C and water will start to flash boil there once the pressure drops. That's one of the reasons modern cars need a sealed system, they rely on it as the coolant is so close to boiling point in normal use.

I'm not sure where you get tap water from - there's no tap water in my cooling system!

It has ready mixed 50/50 coolant in it which is presumably made from distilled water. Boiling point of 50/50 coolant mix at atmospheric pressure (eg with the radiator cap loose) is about 108 degrees, so it would have to have been well above 108 degrees to be boiling as furiously as it was. There's a good article here that shows boiling point, freezing point and specific heat capacity of coolant at different mixtures:

https://hellafunctional.com/?p=629

Pressurising the system does make a lot of different to boiling point of course - according to that article plain water boils at 121 degrees at 15psi, so 50/50 coolant would be a bit higher again.

Almost certainly a random air-lock... I've had the same happen on an Activa a couple of times now.

No real reason, just one of those things...

I'm hoping that's all it is Jim.

If I'm bleeding an already filled system can I do it cold, or do I need to get it hot first ? I assume I would just loosen each bleed screw one at a time from lowest to highest and make sure it dribbles out, then close it before moving on to the next one ? (Unlike bleeding when filling where you start with all of them open at the same time)

[white exec]

That all sounds like an air-lock, probably in the head, that would cause localised boiling, just a tiny bit of which can produce enough steam to create pressure and eject coolant when the cap is released.

Simon, I did say when you were asking about adding Forte, that you should bleed the system (and properly). It could always be something else, of course, but part draining a Citroen cooling system and not bleeding it thoroughly is not the best.

Also, a genuine 90-95C is really nothing to be worried about. One of the 2.5 thermostats doesn't open until 88C, and fully open until 100C ! 70-80C sounds much more of a problem - positively luke-warm.

[CitroJim]

Bleed cold first Simon and then bleed again when hot ('stat open)... The rad bleeder is very important on a V6...

Do all bleeding with the expansion tank cap off or loose. Tighten down only after bleeding and the cooling system has cooled down again.

You know, this could be an early indication of a lazy 'stat...

Might not be a bad idea to replace it even though it's a bit of a game...

[white exec]

Is there any requirement on Xantia for a temporary header bottle on the expansion tank while beeding, a la XM?
Instruction there is also to allow engine to reach fan cut-in temperature at least once, while bleeding.
Rationale behind header bottle is to create enough "head" to displace trapped air, which the expansion tank will not do on its own, due to minimal height above head.

[Stickyfinger]

I always thought the extra bottle was to ensure a low level in the expansion tank did not suck in air. It can drop very quickly when bleeding the system.

[harryp]

I think what is meant by "expansion bottle" when bleeding, is the 4 pint milk bottle, bottom cut off. threads wrapped in tape and inserted into header tank and filled with A/F to provide sufficient head, as advised .

[CitroJim]

There's no need of the extra bottle on the V6 (and 2.1TD) Xantias as the expansion/header tank is above the highest part of the engine - just...

In theory it's needed on other breeds of Xantia (and XMs) with their expansion tanks by the ECU box but I've always got away without...

[superloopy]

But wouldn't an 'expansion' bottle provide a bit more 'pressure/head' alleviating even more the possibility of an intake of air.

Sent from my LG-D855 using Tapatalk

[elma]

I've always found the bottle a pain with the XUD engines, I just fill it up and run it until the thermostat opens then top it up. In the past when I used the bottle I still found they needed topping up after the first run so I ditched it.