[Engine] Expansion tank / possible HG issue help plz!!

[mashipx]

Hi guys,
im pretty new to this forum and ive done plenty of searching current/past threads regarding my problem, but cant find anything thats relates fully to my issue.

I have a berlingo multispace 2.0hdi 2005 plate. 87,000 miles

Ive just recently had a full new belt kit and water pump fitted and the mech who did the work recons ive have a busted head gasket due the excessive pressure and bubbling in the expansion tank.
I was aware of the issue before the belt fit, but as i have no mayonnaise and my oil is untainted i put the down to a seperate issue.

After further reading on here i purchased a head sniffer kit to check for the tell tail signs of leaking exhaust gases.
There is plenty of presure so i didnt even need to squeeze the rubber ball, although i did for good measure.
The blue liquid does NOT turn yellow or even green, it just fades to a pailer blue. I tested the liquid using the exhaust fumes from exhaust via a pipe and it does turn a very pail yellow with a greenish tinge, so i know the liquid is working (I think).

Im praying that the lack of yellow means i dont have a head gasket/block issue and that there might be another reason for the excessive bubbling and pressure.
could it be the oil cooler, or air locks in the system??. the engine runs only slightly hotter than i'd expect and never goes above 90 degrees (at least not yet).
and the coolant is fairly clean considering the cars age. there is an every so slight oily testure and smell to the coolant, but im putting that down to years of work etc being done on the engine.

im considering doing a full coolant flush, change of thermostat and do a radiator back flush to see if it helps.
can anyone help shed some light on the issue, ive avoided taking it to a mech to check as ive heard too many dodgy stories about false diagnosisses.
im not in a position to blindly spend cash on could be's and maybe's. im happy to pay for a HG repair but only when i can be 100% sure.

Thanks in advance to anyone who can help and advise. Cheers

[polar]

if you are not losing coolant i would not worry about it. You could get some k-seal if you are losing coolant it will do no harm.

Note the water pumps on 2.0hdi are famous for leaking out of the central bolt so if you havent been losing coolant and suddenly you start to now you have had the water pump replaced just k-seal it.

[brodfather11]

 Unless its boiling and steaming/ throwing out coolant do as polar says and don't worry about it.  

 An air lock could give you these symptoms, try bleeding it again,

You can check that all the small diameter hoses from the cylinder head to the header tank and radiator  and the pipes they fit onto are clear and not blocked. These let any air/gases in the cylinder head bypass the system and vent directly into the header tank.  If these are blocked you can get symptoms like a c/head gasket leaking.

[mashipx]

Thanks for your replies.
The coolant does appear to be steaming and the bubbling is pretty heavy.
i was told by the previous owner that the expansion tank has a crack somewhere. not sure where, i cant find one.
There is quite a bit of compression release from the cap after ive let the engine cool and tried to unscrew it. i read somewhere it shouldnt do this and if so its another sign of contaminate gases,. but again the test chemicle does not turn yellow, so im guessing the coolant is getting pretty hot and takes a long time to cool.
ive alsao noticed that there is a thin black oily residue on the tank sides. wasnt sure if this was normal until i checked my older 1.9d berlingo and its tank is spotless. so i dont think its looking good at the mo.
will try the flush and refill of the coolant and check the pipes as suggested to see where that takes me.

[mashipx]

Just to add guys, if it is steamig/boiling and starts to throw out coolant, where does that leave me??

cheers

[CourierJim]

Could it be steaming and boiling because the water is not circulating throughout the system properly ie. could your radiator be blocked/restricted internally (maybe inside a rubber hose)? Try that backflush you mention.