Citroen XM Forum

Peter.N. wrote: I think the 16v head is what gives the 2.1 its wonderful flexibility.

Peter

Peter, they are 12v NOT 16v.....

Neil, water and oil ways are in different places in sure but NOT positive, Ive found TWO head gaskets in the shed...

Paul

Paul

Sorry, slip of the keyboard, or more likely my brain

Geoff

The problem with the 8 valve XUD's is that due to having the thermostat in the head - the conventional way, and the complexity of the cooling system it is very easy to think they are full of water when actually there is a large ammount of air trapped in the head beneath the closed thermostat. By putting the thermostat in the return pipe in the bottom radiator hose, when you fill the system the header tank will keep on taking in water until the system including the head is full because there is a free flow through the head to the block, the only part that needs bleeding is the top hose and there is a nipple for that.

Peter

Ah I see, so once the thermostat is open the air lock will be released?


1.9 TD head:



2.1 TD gasket


The only significant difference is on the lower row of water ways on the head between cys 1&2 and 3&4 where one hole appears 'off-set' to the pattern shown on the gasket. I would of thought a slight tinkering of the gasket would overcome this...

On the 1.9 the air will be released but because there is no water round the thermostat it won't open very often until the damage has been done. The 2.1 head is full of water regardless of the thermostat mode because its not in the head but the bottom of the block.

Peter

I would be surprised if a 1.9 8v head even fits a 2.1 12v engine. definitely a retrograde step anyway.

A 1.9 should fit as the XU series blocks are all the same be it petrol or derv and the 2.1 is just a stroked 1.9 anyway, still no point putting a 8v head on a derv though.

D

So why have Cit made an 8v 2.0 HDi? Granted that it's probably down to cost but if they've already developed a 12v head, why put an 8v one on the HDi?

Maybe production cost? with a new HDi engine it must of cost more to produce and so they made savings by sticking with an 8v? would be interesting to know.
maybe as it was a replacement for the 1.9 they started out using the head and block from that engine with the early HDi's?

D

I think the improved efficiency of the common rail unit has got something to do with it, even with the 8v head its producing as much power as the 2.1 although it doesn't produce it as smoothly below 1500 rpm . The 2.1 with the 12v head is also more efficient than the 1.9 in spite of its increased power. In my experience 1.9s will give 45-50 mpg driven carefully, the 2.1 will give 55 which is only 5 mpg less than the HDi.

Peter

It is probably down to cost, but then I think everything on the C5 has been built to a cost - I rekon my Xantia was a better build, it certainly had more poke.
Peter, are those economy figures the papery type one or real world ones?
The best I got out the Xantia was 45, but it was normally low 40s.
My C5 struggles to get 40!
Both of those were brim tests with most of the miles on the motorway at 70.
My BX however will beat the above without trying (but granted, it's a 1769cc)

I'm intending on putting the 2.1 lump in my BX. But to prevent messing about with front mounted intercoolers and to preserve the engine bay layout, I'll use the XUD9TE head.