Expansion tank boiling over

[Mustardmit]

Hi folks.
My expansion tank keeps pressurising and squirting steam and water out through a crack along the seal. It's done it three times so far. After the second time, I waited for the engine to cool off then topped up the water as it had gone down then drove home (about 50 miles) with the heater on full heat and the windows down - no problem either at lights or when I'd got home.
Today I took off, 30 mile journey down the motorway, heating on full blast again (just in case) then it did it again.
Any idea what is the most likely cause? I'm hoping the system might just need draining/flushing and the tank replacing and that it's not a) a failed thermostat (because I know they're hard to access) or b) worse - failing head gasket**.
The temp guage is reading 'normal' ie warms up/needle in the middle.

**I've checked the tank for signs of oil and the oil for signs of 'mayonnaise' - all clear.
TIA for any advice.

 

[trublustu]

It'll be because its split.
Its supposed to be pressurised and this stops it boiling.
A new tank is required. New ones are not expensive. And positively cheap secondhand..

 

[red]

^^ Should be sealed, system is hot and pressurised

 

[JAC]

I had this issue with the Sierra, it kept boiling over, the garage wanted to charge me for all kinds of things but it turned out that the cap was punctured.

 

[Mustardmit]

Many thanks for the answers folks, I'm much relieved. Last time I checked ECP a replacement tank/cap was eleven quid

 

[Mustardmit]

Ok ...new expansion tank fitted an there's still something wrong.

I started it and let it idle to normal temperature (needle in the middle) watched it for a while, fan didn't come on then there was a click (thermostat opening?) hot engine water started bubbling and gushing into the top of the now grumbling expansion tank. Faulty temperature sensor/fan? Solution?
TIA for any expert advice.

 

[CherryVimto]

The 'click' won't be the thermostat as that will open gradually and I very much doubt you would even hear that opening.
But, saying that, if the thermostat sticks until the temp reaches a point when the thermostat frees off and suddenly opens, that MAY account for the sudden boiling......?

The 'click' may be the fan relay operating to turn the fan on. If that's not running check the fuse. If that's ok, you may need to replace the low speed fan resistor. That's located on the bottom corner of the rad fan and has a cable plugged in to it.

 

[Wild E. Coyote]

If the fan relay is done, it will turn on the fan at full blast, but it will turn it on. No way it would let the engine overheat

 

[tractorboy]

Is the thermostat actually opening? Check the rad and rad hoses are getting hot.

Bob

 

[Mustardmit]

[post]344832[/post] Is the thermostat actually opening? Check the rad and rad hoses are getting hot.

Bob

I know this reply is arriving a few months down the line but the problem is still there. I've been driving around with the heating on full blast because this seems to be a temporary 'fix'. No the hoses don't get hot, and the fan doesn't come on ...mysteriously though, the temperature gauge reads normal. What's going on?!!!

 

[748]

Hi
Is there any history of the water pump having been changed?
If not then my advice would be to get it replaced. And while you've got the system drained down replace the thermostat and HCV.
Have a look at this diagram, it may help you to understand what's going on.

 

[Mustardmit]

Thanks for that, no afaik the pump is the original. Looks like I might have to call upon the services of my mechanic friends.

 

[Frank]

[post]352470[/post] I know this reply is arriving a few months down the line but the problem is still there. I've been driving around with the heating on full blast because this seems to be a temporary 'fix'. No the hoses don't get hot, and the fan doesn't come on ...mysteriously though, the temperature gauge reads normal. What's going on?!!!

I won't spend too much time on this answer, but here's a start for you -

Overheating causes (in order of ease of remedy) -

#1. Blocked airflow through radiator - visually check.
#2. Coolant loss/leaks - pressure test cooling system to confirm if required.
#3. Air locks and/or debris in cooling system - drain coolant and check for debris. Refill and bleed system.
#4. Cooling fan full or partial failure - disconnect connector to coolant temperature sensor and run engine. Fan should default to running at full speed.
#5. Thermostat full or partial failure. - with the engine warm/hot, wear glove, avoid fans and belts and squeeze hose leading from radiator to thermostat housing. Hose should flatten and be felt to refill as released. If hose feels solid, then the thermostat is stuck in the closed position.
#6. Water pump full or partial failure - visually inspect and if #1 - #5 are as they should be, replace water pump.

Given symptoms on this and previous posts, then probabilities suggest #5 as most likely. However, steps #1 - #4 still need to be done.

Hope that helps.

 

[Mustardmit]

[post]352502[/post]

[post]352470[/post] I know this reply is arriving a few months down the line but the problem is still there. I've been driving around with the heating on full blast because this seems to be a temporary 'fix'. No the hoses don't get hot, and the fan doesn't come on ...mysteriously though, the temperature gauge reads normal. What's going on?!!!

I won't spend too much time on this answer, but here's a start for you -

Overheating causes (in order of ease of remedy) -

#1. Blocked airflow through radiator - visually check.
#2. Coolant loss/leaks - pressure test cooling system to confirm if required.
#3. Air locks and/or debris in cooling system - drain coolant and check for debris. Refill and bleed system.
#4. Cooling fan full or partial failure - disconnect connector to coolant temperature sensor and run engine. Fan should default to running at full speed.
#5. Thermostat full or partial failure. - with the engine warm/hot, wear glove, avoid fans and belts and squeeze hose leading from radiator to thermostat housing. Hose should flatten and be felt to refill as released. If hose feels solid, then the thermostat is stuck in the closed position.
#6. Water pump full or partial failure - visually inspect and if #1 - #5 are as they should be, replace water pump.

Given symptoms on this and previous posts, then probabilities suggest #5 as most likely. However, steps #1 - #4 still need to be done.

Hope that helps.

Thanks for that Frank, I just made a discovery while going through some of those:
if I grab hold of the water pump pulley, I can easily rotate it with one hand so it slips round even though the belt is wrapped round it as normal. I am hoping therefor that it might just be a matter of tightening the belt (tensioner?)

 

[CherryVimto]

The belt tensioner is tensioned by its own spring/resistance as is and as far as I'm aware can't be adjusted. If it is not tensioning correctly it may need replacing.

Are the 4 bolts that hold the pulley on to the pump still there and tight?

 

[Mustardmit]

Oh bugger, I suspected that - it's expensive :-(
Not sure about the bolts, will check when our driveway dries off again!