Simon's new Xantia V6 and Leaf blog

[elma]

Some high temperature epoxy resin will fix that in a few minutes, a really annoying problem but thankfully cheap and easy to repair. I expect I'll be having a lot of my own problems when I start using my V6 as a daily, all part of the fun but only in hindsight.

[xantia_v6]

You can't run an ES9 with the thermostat removed. it is a bypass thermostat, so with it removed, the coolant will mostly bypass the radiator.

The ES9 thermostat has a piston which slides through a rubber seal to adjust the flow direction. Perhaps the sealant is causing the piston to stick to the seal?

I think that you might be better off without the sealant and with a leaking matrix.

The thermostat and seal are 4 and 8 in the top diagram.

[CitroJim]

Sounds like a (the?) thermostat was stuck shut, blocking off the radiator, but later broke free and opened up. I would replace it.

I would concur...

[white exec]

Mister Auto have Valeo, Febi and other Citroen 'stats in their dedicated housings, if unavailable from Citroen.

[Mandrake]

You can't run an ES9 with the thermostat removed. it is a bypass thermostat, so with it removed, the coolant will mostly bypass the radiator.

The ES9 thermostat has a piston which slides through a rubber seal to adjust the flow direction. Perhaps the sealant is causing the piston to stick to the seal?

You could be right. I can't see what else it could really be other than a sticking thermostat, and its strange that it started sticking now of all times. On the other hand its nearly 20 years old (no sign of a thermostat change in the previous owners studiously collected receipts) so it might have been getting a bit sticky anyway.

Apparently the opening temperature of this thermostat is actually 82 degrees not 88 as I had assumed, so my reading of 82 when cruising at 50mph on the test drive afterwards was probably not a problem after all.

I think that you might be better off without the sealant and with a leaking matrix.

Certainly when I change the thermostat it will get all new coolant and I won't add any Forte back in. Hopefully that will continue to seal the heater matrix without causing any harm elsewhere.

The thermostat and seal are 4 and 8 in the top diagram.

In your list you highlight another seal - number 7, are you suggesting I need that as well ? Or are you suggesting I need all the items in the bottom list as well ??

[Mandrake]

Edit: I guess not everything as the list includes the temperature sensors etc...

However should I get the other mounting seals, and will I have to remove the top housing (and thus those additional seals) to get access to the bottom housing, or can the bottom one with the thermostat be removed by itself ?

Also looking at this guide, does the thermostat housing need sealant applied or should there just be a normal gasket ?? (If so why did that guy add extra orange sealant ?)

http://www.406coupeclub.org/Files/HowTo ... engine.pdf

[Stickyfinger]

I would never use a sealant when there is a gasket....

[Mandrake]

I would never use a sealant when there is a gasket....

I wouldn't either - but is a new face sealing gasket included with the thermostat I wonder ? It doesn't say.

It's a bit pricey, just looked it up in £ inc VAT

Thermostat (1338 73) - £27.38
Thermostat Gasket (1340 42) - £16.16

And for two of seal 7 in the bottom picture (1340 46) £11.80 - but it's not clear whether I'd even need to remove the top housing or not. But if I did have to remove it for access it would seem to be prudent to change those seals.

[Stickyfinger]

The only time I would was if the joint was designed to move (rotate etc) so to give lubrication and prevent gripping/ripping..... rather than just compress.

( as a botch.......maybe if the surface was very badly pitted, it would then be used more of a filler than a sealant and I would wipe most of it into the surface and wipe off any excess)

[Mandrake]

The ES9 thermostat has a piston which slides through a rubber seal to adjust the flow direction. Perhaps the sealant is causing the piston to stick to the seal?

I've been giving some thought as to how the thermostat could end up stuck shut part way through a drive where it had previously been working to regulate the temperature and think I've figured out what may be happening.

As you say the piston is probably sticking to the seal - maybe the Forte has swollen the seal or made it go "sticky", and maybe it gets more sticky when its hot.

In any case, it wouldn't cause it to only stick when closed (like a conventional thermostat) it could potentially cause it to stick at ANY position of travel, closed, partly open or fully open.

When the coolant heats up the piston would expand a bit in diameter and probably so would the seal, and if it was already a bit sticky that extra expansion might make the piston bind completely in the seal in its current position of travel. That would explain why turning the engine off and letting it cool for 10 minutes was enough to "fix" the problem - the engine cooled by about 10-20 degrees, (the fan keeps running on low even with the key off) the piston and seal shrunk slightly and they broke free of each other allowing the thermostat to open again.

So why would it stick in a fully closed position if the thermostat was already open and the engine was already up to temperature ? I think that's pretty easy to explain, and here's my theory.

Prior to that happening the engine was up to temperature and the thermostat was open, then the heat caused it to stick OPEN. Due to being stuck open, when you eased off on the acceleration a bit or cruised at a higher speed the coolant would actually get too cold because the thermostat was staying stuck open - I do remember seeing the reading drop to around 70 a while before it started climbing again in fact.

After a while the cooling below normal running temperature would let the piston shrink and break free of the seal and the thermostat would snap completely shut under spring control. Now the engine would start to warm up again and if the piston stuck to the seal again before it warmed enough to open the valve it would stick in the CLOSED position. This of course would cause the engine to overheat and the hotter it got the more the piston would increase in diameter and the more the seal would swell and get a tighter grip on the piston - at that point you have a runaway condition where it is overheating but the thermostat is stuck fast in the closed position.

The only thing that will break it free then is to turn the engine off and let things cool down for a while.

The "trigger" for the scenario above may be as innocent as getting the engine good and hot through some sprightly acceleration, causing the thermostat to stick OPEN, which doesn't initially cause any visible symptoms, followed by some low acceleration faster driving - say cruising at 50mph with a very light throttle, which will tend to cool the motor down a lot, but due to the stuck open thermostat it cools down too much, then when it lets go and snaps shut the scene is set for it to stick closed and trigger a runaway overheating situation...

It's going to be at least two weeks before I can get the parts and the good weather together to replace it so I'm just going to have to be very careful and only use it for short local journeys. Any sign of the temperature going north of 90 degrees and I'll pull over immediately and turn it off for 10-15 minutes then check the radiator gets warm when I start it up again to confirm that it has unstuck itself. It has been very sporadic so far as its only happened twice in a week out of 12+ journeys so hopefully I can nurse it along until I can replace the thermostat.

I guess we'll find out for sure when I can inspect the seal but due to the peculiar thermostat design with a piston sliding in a rubber seal I think we can say that Forte is probably not a good idea in this engine!

[CitroJim]

This is most interesting Simon. Your reasoning on what might be happening certainly appears sound, given the odd design of the thermostat.

I guess we'll find out for sure when I can inspect the seal but due to the peculiar thermostat design with a piston sliding in a rubber seal I think we can say that Forte is probably not a good idea in this engine!

On that basis, possibly yes, and again original FCF research may once again give the exception to the general rule...

That said, I'm sure I've run the V6 engine with Forte in it with no ill effects... Certainly all the others I have used Forte in has never shown any problems of this nature but then no other has the same design of thermostat as the ES9.

I'm wondering if it might be worth having words with Forte themselves about this and especially about rubber compatibility. I'm sure they'd be most interested. I hope they will listen carefully even though we're not 'trade' - to whom I believe they only supply and deal with.

[white exec]

If you have a bit of Forte left over, or could pinch a sample of Forte'd coolant from the car, you might be able to investigate its 'stickyness' when heated, or otherwise.

[elma]

I currently have forte in my v6 with no adverse effects observed. I think it's more likely just bad timing. I guess the odds are 50/50.

[RichardW]

Simon

Drop these guys an e-mail - (parts at jarigbyechorley.citroen.co.uk) they offer parts at near trade price, and may have the bits in stock and be able to post them out. Postage might kill any saving though....

You won't need to remove the upper housing as it is behind the lower one - the lower one appears to fit over at, where the seal is shown as 6 on Mike's screen shot (and you can see it in the 3rd pic in the guide you linked). I might be tempted to get an O-ring for here, otherwise it's bound to tear on removal!! Only £1.49 (P/No 134045)

I see how it works now - with it out flow would split between the block and the rad - I doubt the pressure drop is that much higher through the rad; I reckon you'd get enough flow in a Scottish winter to keep the temperature in check unless you really cane it. Might be your only choice if it decides to stick shut permanently!!

[Mandrake]

Simon

Drop these guys an e-mail - (parts at jarigbyechorley.citroen.co.uk) they offer parts at near trade price, and may have the bits in stock and be able to post them out. Postage might kill any saving though....

I think I'm just going to order the bits from Citroen Glasgow tomorrow for collection - they're usually pretty quick so they will probably have them in by Friday, and without any postage charge. (It's a good 40 minute round trip walk from work in my lunch break but it wouldn't be the 1st time I've done that walk, or even the 10th! )

I'll order another 5 litre bottle of Triple QX ready mix from carparts4less - I still have an unopened 5 litre bottle from last time I ordered as I vastly over estimated how much I needed for the radiator swap so two 5 litre bottles will be more than enough.

You won't need to remove the upper housing as it is behind the lower one - the lower one appears to fit over at, where the seal is shown as 6 on Mike's screen shot (and you can see it in the 3rd pic in the guide you linked). I might be tempted to get an O-ring for here, otherwise it's bound to tear on removal!! Only £1.49 (P/No 134045)

Ah well spotted - and I see it in one of the picture in the Peugeot article I linked, sitting in a groove near the end of the tube that sticks out after the bottom housing has been removed. If its only £1.49 I'll definitely get it, and because the top housing won't be removed I won't bother ordering two of item 7 (seals for the top housing to the block) as they won't be removed. That will save a few ££.

I see how it works now - with it out flow would split between the block and the rad - I doubt the pressure drop is that much higher through the rad; I reckon you'd get enough flow in a Scottish winter to keep the temperature in check unless you really cane it. Might be your only choice if it decides to stick shut permanently!!

Well I had another scare tonight so it has now become quite urgent. If I can get the parts and coolant by Saturday I might be doing it this weekend even if it is raining.

This morning it was fine but on the way home tonight I think it just remained stuck shut full stop. So it warmed up normally until the point where the thermostat would open, at which point it presumably didn't! Temperature kept rising fairly gradually but by the time I was onto the M8 it was reading above 85 and I realised something was wrong. I had the Lexia plugged in and monitoring the temperature there as well. Normally I'm only on the M8 for about a mile but I discovered to my horror that the Chappelhall Offramp that I normally take seems to have temporarily ceased to exist!! So I ended up going along an unfamiliar section of motorway with no hard shoulder to pull over on and no exits to take for some distance with the temperature gauge going up and up...

I finally ended up creeping along to a roundabout with a blocked off exit leading towards Cumbernauld where I could pull over and switch off - by that point the Lexia read 108 degrees and the Gauge read 100. I also had the heater on full blast (very hot) and the windows open to help it out a little bit.

Interesting thing is I literally only switched it off for 3 minutes, then started it again and the temperature started to plummet back down to normal in about a minute, and according to the Lexia the temperature remained between 82 and 90 the whole way home from where I was - clearly it had unstuck again.

No more motorway driving until this is fixed. I'll have to go via Bellshill tomorrow where at least I can pull over and turn off at any point.