Like I said thermostat housing will be leaking drawing air in when cooling, that's why your seeing bubbles through that pipe, don't spend any money till you change thermostat housing.

no offence but the colour of the coolant and scum has nothing to do with air in the system changing housings will do nothing thats not air its oil mixing with water the problem without a doubt is the oil cooler or head

youve either got a blown head gasket or........

That's what I was trying to say at the start of this thread, quote "If there's still residual pressure that would imply a leak of combustion gas into the cooling system". Pressure build-up combined with unexplained coolant loss = blown head gasket most likely.

It boils in certain places due to air pockets for the sake of £15 just change it they are known for thermostat housing and I put money on HG not been at fault.

I would get a test done on the cooling system for combustion gasses. Decent garage will have the kit to test, only takes 5 mins to test

As already mentioned by Ian, a sniffer test or combustion gas test on the cooling system is required here - look at the colour of that expansion bottle and the cap!

www.fordownersclub.com/forums/topic/18110-persistent-thermostat-problems-i-think/

This is what you have to avoid.

Any news

Got the replacement hose now and thermostat housing ordered for arguments sake, fingers crossed but as said previously the colour of the bottle is worrying! Its looking like a job for next weekend not this one unfortunately. 

I can say had the same thing, there was some overheating ,over pressuring and bits of scum in the header tank  I changed the housing and the rubber seal had completely disappeared. The problem is the water dries before its visible, while your doing the job make sure the 2 narrow pipes are clear to the header tank there to release pressure via cap if there blocked they will force the water out somewhere else. There are restrictors in the pipes (please no radweld) that might be blocked.about 200 mm from header tank.

 

found the post from years ago that helped me.

 

http://www.bba-reman.com/forums/PrintTopic121332.aspx

The car has done 30k since the problems, still no head gasket symptoms, although I would of put my life on that been the problem.

You fill me with hope James! I will be sure to check the pipes for blockages and give them a good blast out when I do the job.

So when you doing this job then?

Job kind of done, the new thermostat housing was of poor quality and he bevelled nuts in the unit were unsuitable and withdrew from the housing. I therefore fitted the new seal to the old housing and ran with that. I drove around Stoke over the weekend at no more than 40-50mph for around half an hour at a time and the car did not loose any coolant after covering approx. 30 miles. The coolant rose above the max level so must have been held under pressure.

Drove from Stoke to Sheffield last night using A50-A38-A61, checked the bottle immediately after the journey and there was a small amount of coolant inside which drained away in less than 5 minutes after I arrived. No evidence of leaks onto the ground.

So it seems the extra engine load has caused the loss, I have been made aware that the thermostat housing itself can warp and I have obviously not solved the problem as this may still be an issue. Awaiting a Circoli housing from euro car parts now so fingers crossed it will solve the issue.

You checked both the pipes were clear from header tank, like took both ends off and blew down pipes? Just read the post again you never changed it, they suffer from small cracks not really visible, gonna have to get another one.

In fact you have done the complete wrong job,it's the back of the housing where it connects to engine block.

I aggree with MJT head gasket. Brown froth mixture of oil in coolant. Common fault.

Boiled radweld don't look to good, virtually impossible to do HG on 1.8tdci, allegedly.

Contact Iantt. He'll guide you through it. Surely if the engine's been built, it can stripped.. and built again..

Timing belts are the easiest jobs to do, but it's rewarding when you step back and admire a finished job

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The trend seems to be towards throw-away engines. When I read through the Haynes for our new 1.0Litre EcoBoost I was quite shocked to discover how little can be done. The top-end can still be worked on but the block and bottom-end are manufactured as a piece and if split can't be successfully reassembled.

The old 1.8TDCi, fortunately, doesn't fall into this class.

9 hours ago, james1089 said:

In fact you have done the complete wrong job,it's the back of the housing where it connects to engine block.

My intention was to change the whole housing but as I said once I had fitted the new housing inc. seal upon tightening the thermostat cap the beveled nuts withdrew. Apologies my post was unclear :)

18 hours ago, james1089 said:

You checked both the pipes were clear from header tank, like took both ends off and blew down pipes? Just read the post again you never changed it, they suffer from small cracks not really visible, gonna have to get another one.

Yep both were clear and had no visible leaks. What is the best way to check for small cracks in these? They must be tiny if there are any!

5 hours ago, frund said:

I aggree with MJT head gasket. Brown froth mixture of oil in coolant. Common fault.

But there is no film of oil on the coolant? Even on draining the coolant fully there is no film on the entire contents?

5 hours ago, james1089 said:

Boiled radweld don't look to good, virtually impossible to do HG on 1.8tdci, allegedly.

Lets hope the scum inside the tank is the boiled Radweld. When you say virtually impossible, do you mean solving the issue?

3 hours ago, mjt said:

The trend seems to be towards throw-away engines. When I read through the Haynes for our new 1.0Litre EcoBoost I was quite shocked to discover how little can be done. The top-end can still be worked on but the block and bottom-end are manufactured as a piece and if split can't be successfully reassembled.

The old 1.8TDCi, fortunately, doesn't fall into this class.

Welcome to the new throw away world! Is is biodegradable too? ;)

I have spoken to a mechanic that my father knows, he says it is a common problem that the thermostat housings warp hence giving a poor seal between itself and the block. I have now got a Circoli housing from Euro Car Parts so fingers crossed on that one! Also, if it was HG he said £500 all in inc. machine shop skimming.

It makes sense to try the easier options first as long as they're not too expensive so I hope your new housing fixes the problem. I'm still bothered by the residual pressure though. In spite of all that's been said I don't think there should be any when the engine has fully cooled down. I can't see how your description of coolant flooding back into the header tank when you release the pressure cap squares with a leaking thermostat housing.

Only pressure if their is a leak or blockage somewhere, while it cools air should be drawn in from header cap but leak in housing will draw in air instead trapping in the middle of the system. Still these thermostat housings made of plastic last not much mote than a year. I once searched ebay about 10 different sellers all sold 100s each, when you consider only 5% would buy from ebay it's a fair few. The pipes won't be cracked if their not blocked don't worry about it.

New thermostat housing fitted, I have a 70mi. drive this evening so that will be telling time. When fitting the thermostat housing I wasn't able to get a watertight seal between the housing and the cap which is provided by the thermostat o-ring. When you look at the thermostat o-ring provided with a new thermostat here:

http://www.eurocarparts.com/ecp/c/Ford_Focus_1.8_2008/p/car-parts/cooling/car-cooling-parts-and-car-heating/car-thermostat/?209590290&1&f499e552a31fb2d074cd875d0b451ee2a2e7fd87&000325

It appears much thinner than the one stocked alone:

http://www.eurocarparts.com/ecp/c/Ford_Focus_1.8_2008/p/car-parts/cooling/car-cooling-parts-and-car-heating/thermostat-housings-gasket/?200590150&1&254c9c87e45a3b1d9652738956a75fd1985c4a92&000574

I brought this thicker looking seal and when seated in the housing sat around 2mm proud which allowed a good seal between that and the cap. No visible leaks now, fingers crossed!

Here's hoping, one more thing to try if this doesn't work, get some 1 to by-pass oil cooler by linking the pipes together might be blocked. Try the easiest 1st though although it is simple, don't know if its like the mondeo with an extra thermostat in there or just constant flow. They do cause problems like dumping litres of oil into coolant. Sometimes water seems to becoming from the thermostat gasket when the housing is actually cracked at the back.

while it cools pressure is vented from the header cap not drawn in its a sealed system only a tiny amount of residual pressure stays in the system when cooled when hot it has a lot of pressure that's how the system works