Mark wrote:
"Mrcheerful" wrote in message
om...
Mark wrote:
"Chris Whelan" wrote in message
...
On Sun, 19 Apr 2009 13:01:34 +0100, Mark wrote:

"Mrcheerful" wrote in message
om...
Trevor Smith wrote:
"Mark" wrote in message
net...
On the motorway last night and noticed my Sierra running very
cool. Temp gauge always gets about a third up the scale and
stays constant, but last night it was fluctuating between the
edge of cold and only a tad above.

If the thermostat change doesn't work it could be the
temperature gauge sender that's giving a false reading. As
regarding the heater, a mate of mine had a F reg pinto sierra
and the heater on that was crap, he tried everything to sort it
including flushing the matrix with fernox and it still wouldn't
demist the screen in winter. He's now got an escort and you
could cook on the heater of that. Trevor Smith

flushing doesn't work when they are gummed up, the liquid
physically can never get to the end of all the blockages, it just
goes round one of the open routes and cleans that. the escort
and sierra rad are very similar size and shape so performance is
close to identical, both are very good heaters unless blocked up.

I'm not bothered about the heater I never get cold in a car and
prefer driving on the cold side and it works well enough to
demist. Mainly curious (and it is only curiosity) about the
varying water level. As I said, it drains and fills very quickly.
Must be about two pints up and down. Cycles over a minute, but
the drain or fill is very fast (about 5 seconds)

Mark

I've seen this happen when there is an airlock in the system.
Usually, if you let it warm up to fan cut-in temp with the
expansion tank cap off, it will eventually push the air out.

Of course, with a non-working t'stat, it's going to take forever to
get that hot!

It's not randomly going up and down like an air lock. You could set
your watch by it. Did get warm enough yesterday. I'd say stat is
unreliable more than permanently open. Or may have been because it
was a very warm afternoon and I'd been holding it in 2nd at 30 for
ten minutes.
Anyway, its not a problem, just wondered if anyone had actual
experience of seeing this on a 1.8 CVH.

Mark

that is symptomatic of an air lock, but if it continues indefinitely
then it would imply that air getting in, often through a head gasket
leak. first check the little breather hose that goes to the top of
the expansion bottle, take it off, with the engine running hot water
should flow out of it steadily (hold it over the open top of the
bottle) if none comes out then check where it goes onto the engine
for a blockage. If it comes out ok then check that the passage way
in the top of the bottle is clear. Normally this pipe will let out
any air from the system rather than it be forced up through the
larger pipe to the bottom of the expansion tank.

Yep all flowing well out that pipe. No need to remove it as can see it
flowing out with the expansion tank cap off.

I not investigating this or trying to fix it as its done it for the
last 3 years and car works well enough, just curious if anyone else
had it.
Mark

Sussed it, it is getting to near boiling point, water rises, thermostat
opens, cool comes in and level drops. With a new stat and good antifreeze
in it will probably stay near enough level.