car starts fine but within 10 seconds the top hose is rock hard
switch off engine release pressure in coolant bottle
replace cap
car is fine for the rest of the day
car does not overheat at all sets at 98 deg all day even in traffic
no smoke
there is no water loss
anyone pleassssssse

98 is rather high, ours sits at just over 90 (as you'd expect as the thermostat starts to open at 92, nominally).

It sounds rather like a HG problem, as that's the only way I can see the coolant system pressurising so rapidly.  Why the coolant isn't going the opposite way to the combustion gases when it gets a chance is a bit of a mystery...

Perhaps the leak is past a fire-ring of the HG, but only when the engine is dead cold, and after switch-off the coolant depressurises before the leaky bit opens up again. ???  :-/

Keep a close eye on the coolant level.

Hope I'm wrong about the headgasket.  How many miles has the engine done?

car has done 87000
i assume its 98 deg
it is just above the line between 90 and 100

Gauge accuracy is not great and the calibration of the face varies between cars. As long as it sits roughly mid-gauge during driving and the fans keep it from going much above mid-gauge in traffic that's good enough.

The cooling system is meant to pressurise as it warms up but it's a gradual process and won't happen within 10 seconds from a cold start (assuming that's what you meant?).

If you run it without the expansion tank cap do you get a stream of bubbles through the coolant?

Also - what engine are we talking about? Very rare to get this type of head gasket failure on a V6 but it's not unusual on the 4 pots.

Kevin

just started it
took the cap off there are no bubbles in the bottle, left it running for 20 mins was watching the bottle throughout
the car is a 2.5 v6

redravern wrote on 28. Apr 2011 at 11:16:

just started it took the cap off there are no bubbles in the bottle, left it running for 20 mins was watching the bottle throughout the car is a 2.5 v6

Doesn't sound like you have a big problem then, and it would be very unlikely on a V6 anyway, IMHO. What happens if you don't release the pressure?

Kevin

Water pump?

Blocked Rad?

Martin Imber wrote on 28. Apr 2011 at 11:45:

Water pump? Blocked Rad?

Could be, but it'd be constantly overheating (i.e. boiling over) if it was driven like that? :-/

Trapped air?

Does sound odd

Kevin Wood wrote on 28. Apr 2011 at 11:42:

redravern wrote on 28. Apr 2011 at 11:16: just started it took the cap off there are no bubbles in the bottle, left it running for 20 mins was watching the bottle throughout the car is a 2.5 v6 Doesn't sound like you have a big problem then, and it would be very unlikely on a V6 anyway, IMHO. What happens if you don't release the pressure? Kevin

dont know i will try tomorrow when its cold again
thank you

Martin Imber wrote on 28. Apr 2011 at 12:00:

Trapped air? Does sound odd

http://www.wrongdiagnosis.com/sym/trapped_air.htm

;)

didnt release pressure nothing happened pipes were hard but did not get any harder left running for 20 mins or so.

local garage said to try changing the cap?

Sounds to me like it's behaving itself. It should pressurise to the point that the hoses are hard. The fact it was happening so fast made me worry, but if it doesn't blow the expansion tank cap then I don't think you have anything to worry about.

Kevin

cheers all  :)
my mind is at ease for a while :y