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[steve2000ng]

Hi, this is my first post.  I am really at a loss, please help
I have flushed out the radiator, and tried to flush the engine, but cant get any water through it
if i run the car, it pressurises the systen so much that the pipes go hard and it gushes out of the header tank
the guage (both in the car, and on a code reader) says the temp is around 99 degrees
both pipes on radiator are hot, heater is hot.  i really dont want it to be anything serious, but i guess it will be
rad fans also seem ok
any ideas

[martin42]

rad could be at fault

[steve2000ng]

rad seems clear, have put gallons of water through it

[omega3000]

I had a similar problem that took a while to get sorted but after one thing and another it was all down to the rad being blocked 

Any water loss/leaks ?

[steve2000ng]

no water leaks, just flushed rad out again, totally clear.  Took thermostat out, (what a job), and teasted it on the cooker, that seems fine, Any suggestions ?

[Darth Loo-knee]

So you say your radiator is not blocked, also your thermostat is workng fine. You say water is gushing out of the reservoir when is this happening? Have you started the car from cold? Have you got the air out,?

[omega3000]

I took my radiator off many times and thought it was clear but after many times of re-fitting it was found to be partially blocked at the bottom i think . Once the car is warming through the pipes feel the radiator to see if its getting warm top and bottom , mine was only feeling luke warm in various parts so as soon as i replaced the rad for another the rad was warm all over pretty much instantly once the car was up to temp ... i did many miles testing before i replaced the rad and the car would boil over same as yours after 6-10 miles . Not saying it is that but it does sound very similar , i too replaced the stat but to no avail . Since the replacement rad has been put on 3 months ago i have not had any overheating issues 

[Kevin Wood]

A couple of possibilities, I reckon:

Expansion tank cap is faulty and venting at too low a pressure
Water pump is faulty causing insufficient coolant circulation and localised boiling.
Radiator clogged up, as said.

Try starting from cold and checking the temperature of the radiator hoses. Top hose should get very hot as soon as the thermostat opens. If bottom hose also gets very hot at this time, I would say the radiator is suspect. A good radiator will hold the return temperature low for a good few minutes, especially if the A/C fans in front of it are running.

If both hoses are quite slow to warm up once engine is hot, and heater on "Hi" is not that effective, I'd suspect the water pump.

But it might be worth trying a known good header tank cap, as if that lets go before it should, insufficient pressure will be in the cooling system to stop it boiling over.

I suppose there are no signs of an oil cooler failure (oil in the coolant)?

Is there a history of an oil cooler failure in the past (may have contributed to the radiator clogging)?

[steve2000ng]

Thanks for all your replies , so far
The radiator pipe at the top gets hot quickly, the pipe at the bottom, stays cool for a time, then gets hot.
The heater in the car is boiling hot
I am going to try the easiest option next, and try a new header tank cap
Will let you know  !!!
( by the way, fitted a new thermostat, while it was out) what a job that was, on a v6 as well  !!!

[Kevin Wood]

You say the fans are OK.. Do they come on once the temperature has climbed a little over the mid-point on the temperature gauge?

Also, where is the temperature gauge normally at when it blows the expansion cap?

[steve2000ng]

Well, tried a new cap, only to find that it wouln't tighten onto the expansion tank, on inspection i found the thread on the tank had partially gone.  I bought a new expansion tank from main dealer (none in scrap yards) cost £38. fitted it with the new cap, and PROBLEM SOLVED, I think the old cap tightened up then slipped the theads when it was under pressure.
WOW and i was thinking head gaskets and everything,.  Not cheap for what it was but it fixed it for me.
THANKS FOR ALL YOUR HELP ...

[omega3000]

Keep an eye on it , i replaced a few things only for the problem to re occur ie rad blocked 

[steve2000ng]

Will do.... Thanks