My BMW 318i has had a new expansion tank fitted after overheating and splitting.After bleeding the cooling system it seems as though the bottom hose is not getting hot any suggestions would be welcome

You may have air in the cooling system, you need too bleed it using the bleed point on the top right of the radiator as you stand in front of the car

Just because the headgasket was replaced doesn't mean its sealing.The head itself could be cracked or warped if the previous owner badly overheated it. Can you confirm if the shop who replaced the headgasket had the head checked for straightness and cracks?

I am not familiar with this particular expansion tank, but with the e36 expansion tank, when it starts to crumble inside, it tends to pull air into the cooling system and cause problems. e36 tanks usually last 10-12 years before they start to crumble, but it is a possibility.
Do you turn on the key and turn up the heater so the heater valve opens when you are bleeding it? I run mine up on ramps so the bleed point is higher than the heater valve when I bleed them. The book does not say to do that so I don't know if it helps at all.

A BMW that is hot after only two or three miles generally has air in the cooling system. Did you turn on the key and turn up the heater to open the heater valve, and then pour water unto the expansion tank until pure water came out of the bleed screw?

Are you talking the expansion tank? If so - Drain coolant first by going underneath the car and take off the protective shield and unscrewing the blue plastic screw (make sure the car is NOT hot!), under the reservoir you'll see an electronic sensor - carefully twist is a 1/4 turn counterclockwise and gently pull downward to remove this sensor don't force it, you don't want to pay $150 to replace it. Disconnect the hoses on the top and bottom of expansion tank by pulling up the metal tabs upwards then pulling the hose away from the tank. I believe there are two or three screws which hold the expansion tank bracket in place, unscrew these and pull the bottom of the tank away from the radiator then lift upwards on the bracket (the bracket and expansion tank should then come out). Get the old expansion tank off the bracket and replace. You want to take off the bracket because getting a new tank on the bracket is a B*TCH!

Reconnect in reverse order.

Make sure to bleed the cooling system properly to remove air pockets (please use BMW coolant and distilled H20 in 50/50 mix - it's not the same as your Prestone or other mass produced coolants). Last replace the expansion tank cap because that might have created the expansion tank cracking.

Good luck and hope this helps

It could be due to age. Split hoses aren't uncommon.
However, it could be due to either a radiator blockage or a cylinder head problem - which is allowing exhaust gases to find their way into the cooling system via a leaking head gasket. When this happens the cooling system becomes pressurised by the exhaust gases.

To check if your radiator is blocked, run the engine until it is hot. The coolant goes into the radiator via the top hose and into the engine through the bottom hose.

Carefully feel the top and bottom hose. If the bottom hose feels much cooler than the top hose, then that indicates a radiator blockage. If the bottom hose feels 'flat' and 'squashed' that is another indicator - though it also can point to head gasket problems.

To check if there are head gasket problems, first check the oil on the dipstick. If it is a 'creamy sludge' then that indicates coolant has found its way into the lubricating system via a leaking head gasket.

Also remove the cap from the raditor expansion tank (where you fill it with coolant/water). Is there any sign of oil/sludge in the expansion tank? Another sign of head gasket problems.

With a COLD engine, remove the cap from the radiator expansion tank and then fire the engine up. Watch the coolant as the engine ticks over ... at first bubbles will appear as air in the coolant escapes. The bubbles should stop after a few moments as the engine warms. If the bubbles continue -or there is 'violent bubbling' that's teling you there is a head gasket problem.

I presume that your car hasn't been overheating or 'running rough' at times, as you haven't mentioned that. Overheating and 'running rough' can also be symptoms of head gasket problems.

All being well .. no radiator blockage or apparent head gasket problems, it is more than likely that the hose burst due to age/mileage.

check concertina hose between air flow meter and engine for splits cracks etc. check your radiator is topped up and that you have bled the cooling system, the bleed valve is beside the expansion tank.

Hi. Normally if the pipes or hoses are too old, it's normal to get burst especially if your car is lack of Service Maintenance. Another thing is if the engine is overheating and the expansion tank cap is faulty (stuck Close), the weakest parts of cooling system will burst.
When you replaced the damage parts I suggest you to replace Thermostat Valves as will. Also I would suggest after the repair to do Cooling System Pressure Test encloding Expansion Tank Cap pressure test, Bleed cooling system properly, Monitor Coolingling Fan and Engine Temperature Operation.
I hope this tip will help you to solve your problem and if it's still existing I hope you don't mind to inform me and I'll try my best to help you as much as I can.
Thanks and good luck

the fan is the problem, try replacing the temperature sensor that the fan connects too

Check to see that the expansion tank is not broken or if not u have to do a leak test on the car .....if everything is fine then u have 2 bleed the car with heater on full blast