405 TD Cooling system pressurising.

alanshep · Post by **alanshep** » 23 Dec 2009, 17:56

Hello - looking for some advice please. The car is a Peugeot 405 TD.

Yesterday morning when I got in the car the coolant level warning light came on. I checked the header tank - the level was low- so topped up with antifreeze and went to work. Did about 40 or 50 miles throughout the day without further apparent problem.

This morning I've had a day off work to do some shopping. When driving the car on a couple of occasions the coolant level light came on. I pulled over and each time coolant was expelled when I removed the header tank lid and the system seemed quite pressurised - I immediately thought the head gasket must have failed.

When I got home I tried bleeding the system using a funnel in the header tank as recommended, expecting to see bubbles in the coolant. With the engine running the level in the funnel rises steadily but no bubbles. I found that when I undid the bleed screw in the thermostat bypass pipe it frothed as if gas or steam was escaping and the level of the coolant in the funnel held steady.

The cooling system is obviously getting pressurised internally. I still tend to suspect the head gasket but I don't understand why the pressure doesn't produce bubbles in the header tank. This set me thinking that instead the water pump (which was new this time last year) might have failed and might be causing the engine to 'boil' inside?

Any thoughts appreciated.

Regards

Alan

deian · Post by **deian** » 23 Dec 2009, 19:37

hi,

i would also suspect the head gasket, if you think it's steam from the engine boiling due to the faulty pump then is the engine running HOT, water/oil temp gauge would show this.

i had a pug 106 that had exactly the same problem, turned out the head gasket was gone on one of the exhaust channels and the water/exhaust was missing, hence the pressure and missing water.

so this explains the pressure build up, and this would only happen if the system was sealed, the gas would escape out of the water into the space in the top of the coolant resevoir where it would build up the pressure, hence no bubbles, you would see tiny bubbles within the system hence the froth from the bleed screw, doubtful you would see visible bubbles coming up into the coolant resevoir as such, more likely to be disguised as the froth, but the gas would be so dispersed that you wouldn't see much, the water maybe cloudy though

you would only see 'bubbles' if the system allowed one large amount of exhaust to come directly up into the reservoir through the water, but because it's constant and gets mixed it would never bubble up as such

the gas would also collect at the highest point in the system, i.e a bleed screw unless your resevoir is high up agaisnt the bulkhead or something

so again, the engine should get hot, how does the radiator feel after a run? check top and bottom (where the hose comes in at the top, and the hose comes out of the bottom).

my money is on the head gasket

hope that helps

Post by **CitroJim** » 23 Dec 2009, 20:07

I concur with you Dei, sadly the head gasket is prime suspect

The expansion tank on a 405 is in the same place as a 106, down by the side of the rad...

Still, it's not a massive job on a 405. Evilally in his Glowplug Woes thread contains loads of useful information on doing the job.

evilally · Post by **evilally** » 23 Dec 2009, 22:21

Yep, if you want an idiots guide to changing a head gasket that's the thread to read

If I can do it, then probably everyone and their mother can do it. Why can't these things happen in summer