steam coming from expansion tank cap

Hi my mgf has just starting blowing steam through the expansion tank top fans all cut in when engine temp is at right temp heater only blows cold air it's pushing water into expansion tank but after a while seems like somewhere there's a block in it and just falls up and then steam erupts I have put a new cap on the bottle but it still does it any ideas please

Chezphil wrote: Hi my mgf has just starting blowing steam through the expansion tank top fans all cut in when engine temp is at right temp heater only blows cold air it's pushing water into expansion tank but after a while seems like somewhere there's a block in it and just falls up and then steam erupts I have put a new cap on the bottle but it still does it any ideas please

Bleed all three points with heater valve fully open and run up to temp again if it still does it change expansion cap and try again, if that doesn't help I would suspect head gasket and system pressurising from exhaust gasses.

Sent from my SM-J500FN using Tapatalk

Probably a leak, and its now airlocked. Refill and bleed the system from all three points and then see if your water level stays put. Check you have a return flow back into the expansion tank too. Maybe a faulty water pump or a blockage in the system.
If you could get one, try a coolant pressure tester on the system to check for leaks that way.
One final thing, coolant strength is paramount, has the coolant been replaced in the last two or three years, if not, the coolant may have degraded and you may have frozen coolant damage in this recent spell of sub zero temperatures.
Sundance

Thanks for that will bleed system tomorrow there are no visual signs of hgf no gunk on oil stick or cap and no oil in water

Good point on recent cold snap was fine last week and just started happening after the snow and beast from the east any way of checki5 for frozen pipes etc I am going to flush and bleed the system on my day of

Not really sure how to check for frozen up pipes, except maybe pull a pipes off and see if there is any issues, I would expect now its warmed up a bit, any coolant would be liquid by now. I would pressure test the system, but that's easy to say as I have a kit to do that.
I think fill up the tank, bleed and then look everywhere for leaks including seeing if there is any mayo on the dipstick.
Good luck.
I had a similar issue on my previous TF and it was airlocked and low on coolant. I think the leak was on the Tee piece connector where a pipe had split. To make matters worse, a stone had jammed my rad fan and blown the fuse, so there was no forced cooling on the radiator either. Best check your fan works too...pull off the engine temperature sensor plug and the fan should fire in!

Sundance

If the anti-freeze concentrate is too low the radiator can freeze up as you drive.

Happened to my mothers car a few years ago (she always filled radiator with water!)

Car overheated, but no permanent damage was done!

Thanks for that no mayo anywhere going to bleed system tonight and see fingers crossed

Just a quick update bled the cooling system heater now blowing hot air no more steam out of cap fingers crossed all sorted thanks for all the pointers now I can crack on with the bit of rust and change the roof withe new one which came with it a bit of other fettling and be ready for that sunny day

Nice work, keep a close eye on the coolant level and fit a low level sensor if you can, could save your engine one day.

Sundance