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Robert, BMW Technician
Category: BMW
Satisfied Customers: 4708
Experience:  Fully qualified 19+yrs exp/self employed technician in the UK
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I have a 1998 520i that keeps overheating. My local garage

Customer Question

I have a 1998 520i that keeps overheating. My local garage changed the thermostat, water pump and fan but it is still overheating. They said they thought it must be an air lock and they have tried to flush through the system to unblock it. They have tried this 4 times but unable to clear the blockage. They have told me they are out of ideas and the only thing left to do would be to take the engine apart to have a look. Obviously this is a non-starter as the car is not worth a lot. Is there anything else we can try before I scrap the car?
Submitted: 3 years ago.
Category: BMW
Expert:  Robert replied 3 years ago.


Hopefully i can help..

How long does it take roughly to actually register its overheating?

Any unusual smoke from the tail pipe since this fault occured?

Do you still get heat inside the vehicle from the heater/blowers?

Any significant coolant loss or increased pressure in the reservoir?

Can you supply last 7 digits of vin number?

Customer: replied 3 years ago.

Hello Robert

It is still at the garage but I have just spoken to them and hopefully this helps:

It takes about 10 mins from cold to over heat when being reved at 2000 rpm and obviously longer when idle

No unusual smoke

Heat is on and off from heater/blowers which is why they beleive it is an air lock

There is increased pressure

Vin number last 7 digits - BM38220

I look forward to hearing from you


Expert:  Robert replied 3 years ago.

Hi..there thanks for your responce..

I do know these can be pretty difficult to bleed at some not sure wither they tried this or not as you dont say..but when ever we had them in in the past we filled them up up the car up at the front jacked up the radiator at the front is at the highest point..and can help get the air out the matrix..of course the heater has to be a fully hot setting..before you bleed the system via the bleed screw...I would imagine givin all what you have replaced so far..they have checked for possible headgasket issues..if as you say you get an increase in pressure in the system you want to see wither this isnt being cause by a faulty headgasket and allowing exhaust gas to filter into the coolant system and cause an increase in pressure building up in the circuit..a proper combustion leak detector kit for head gasket leak detection should verify that or not..have they inspected for a partically blocked radiator,back flushing can help but they maybe able to check that using a digital infra red thermometer...I do hope this helps..if you need to ask anything else or include anything further then just continue before you rate