Coolant bleed nipples Peugeot 405 1.6i XU5M

This is the Forum for all your Peugeot Technical Questions, Problems or Advice.

Moderator: RichardW

BertPleizier
Posts: 7
Joined: 12 Jun 2020, 21:29

Coolant bleed nipples Peugeot 405 1.6i XU5M

Unread post by BertPleizier »

Hello,

I can only find 2 coolant bleed nipples on my Peugeot 405 1.6i XU5M engine (one on top of the radiator and one near the thermostat both marked in red). Please see attached pichtures. I miss one on the thermostat housing itself (like the Haynes manual shows), marked in green. Am I right? This is strange because everything is original to my engine and I am still the first owner so I know whats repaired in the past.

When I order a new thermostat housing cap I get one with a extra bleed nipple on it. Is this a upgraded part from Peugeot?
Attachments
405 Ontluchtingsnippel thermostaat.JPG
405 Ontluchtingsnippel radiateur.JPG

User avatar
Oldpug
Posts: 383
Joined: 07 Aug 2010, 11:15
x 32

Re: Coolant bleed nipples Peugeot 405 1.6i XU5M

Unread post by Oldpug »

Your photos show a perfectly normal set up, no need to change it. I think a bleed valve in the stat cap is for the radiators without a bleed valve. Think about it, stat cap or rad top, they are at either end of the top hose so both do the same job.
By the way, I think you will also find a bleed valve on the heater hose near the bulk head.

BertPleizier
Posts: 7
Joined: 12 Jun 2020, 21:29

Re: Coolant bleed nipples Peugeot 405 1.6i XU5M

Unread post by BertPleizier »

Thank you for your replay. I agree with you that both bleed nipples (on top of the radiator and on the thermostat cap) will do the same job. But when I look in Haynes I see this bleed nipple in the drawings. I can not find a bleed nipple on the heater hose near the bulk head (to the heather matrix). Just 2 pipes.

One more question: there is no bleed nipple just before the thermostat, how can you then bleed the system corectly? I mean when you fill up the system air gets traped before the closed thermostat and the thermostat has to open to let the trapped air out to the radiator. But when there is air around the thermostat instead of coolant it will not open, or am I wrong?

User avatar
white exec
Moderating Team
Posts: 5969
Joined: 21 Dec 2015, 13:46
x 981

Re: Coolant bleed nipples Peugeot 405 1.6i XU5M

Unread post by white exec »

After refilling a cooling system, bleeding needs to be done while the engine is still cold, and then while and after the engine gets up to full working temperature (indicated by the cooling fans operating several times). This ensures that bleeding is finally done with the thermostat fully open, thus getting over the problem of a shut thermostat which you describe.

For many engines and installations, a temporary header tank (eg upturned bottle with base cut off) - fitted into the normal header tank - helps drive out trapped air.

BertPleizier
Posts: 7
Joined: 12 Jun 2020, 21:29

Re: Coolant bleed nipples Peugeot 405 1.6i XU5M

Unread post by BertPleizier »

I imagine me this: I fill the empty cooling system by pouring coolant into the radiator. The coolant fills the bottom of the radiator and the lower coolant hose to the engine and after that the engine block and heather matrix with the endpoint the closed thermostat. After that the top radiator hose fills to the thermostat.

The air in the engine block is trapped at the highest point at the end. This means that the thermostat is not surrounded by coolant but by air, because the air can not go further (thermostat is closed) and can not go back downwards (air will not do that).

When the engine warms up, the coolant in the engine starts to warm up. The air just before the closed thermostat will not get hot, so the thermostat will not warm up en will not open to let the trapped air through back to the radiator (where you can bleed it out). In that case I have a very hot engine with a closed thermostat. How do you get the thermostat to open?

I hope you understand my point, it is a little difficult to explain.

User avatar
myglaren
Forum Admin Team
Posts: 17651
Joined: 02 Mar 2008, 14:30
x 868

Re: Coolant bleed nipples Peugeot 405 1.6i XU5M

Unread post by myglaren »

There used to be a jiggle valve in thermostats that bled out any trapped air to allow the system to fill. There would still be air pockets at high points that the bleed nipples were there to let out.
Couldn't say if they are still included or if there is an alternative method now that thermostats have become such complex creatures.

User avatar
white exec
Moderating Team
Posts: 5969
Joined: 21 Dec 2015, 13:46
x 981

Re: Coolant bleed nipples Peugeot 405 1.6i XU5M

Unread post by white exec »

That's correct - many thermostats have a small by-pass (leak) built in, to avoid total shut-off and the problem of the 'stat becoming surrounded by air. Some just have a tiny hole, others a slightly larger one with a small and loose ball/pin inserted.
'stat with jiggle pin 4.jpg
'stat with jiggle pin 4.jpg (20.53 KiB) Viewed 27 times
You describe the filling process very well, Bert!

BertPleizier
Posts: 7
Joined: 12 Jun 2020, 21:29

Re: Coolant bleed nipples Peugeot 405 1.6i XU5M

Unread post by BertPleizier »

Thank you! That sounds simple. And I guess that when you have a thermostat with a small hole, you have to put the thermostat in with the hole upwards (at the top) of course. Now I have the answer to all my coolant bleeding questions :D.

BertPleizier
Posts: 7
Joined: 12 Jun 2020, 21:29

Re: Coolant bleed nipples Peugeot 405 1.6i XU5M

Unread post by BertPleizier »

And what to do when the new thermostat don't have a small by-pass build in? I have Googled some images of thermostats and not many have a by-pass.

User avatar
white exec
Moderating Team
Posts: 5969
Joined: 21 Dec 2015, 13:46
x 981

Re: Coolant bleed nipples Peugeot 405 1.6i XU5M

Unread post by white exec »

Either ignore it (which is what most folk would do), or drill a small hole in the periphery - 1.5mm maximum, and position at 12 o'clock - if you want to be sure air will not get lodged there.

Important NOT to make this hole too large, otherwise you could have a problem in really cold weather in keeping the system up to working temperature. A sizeable hole will be akin to a leaky thermostat!

I am reluctant to suggest the drilling, but it is obviously something that you're concerned about.
Might be a good idea to buy a couple of new 'stats, just in case it backfires.