Help Needed!

Dear all, I have got a 1996 318IS. Recently I felt the airconditioning is not very cold, therefore I took it to a shop for inspection. The guy said its the Heater Control Valve thats faulty. I didn't fix it straight away until today I replaced the Heater Control Valve by myself. Strangely after I replaced the Valve, the air con is now working fine, the heater is working fine, but after a short period of travel, the car starts to overheat badly.

What can I do? What is the proper procedure for flushing the coolant? is it the coolant?

Anyhelp will be greatly appreciated!

Sounds like air in the cooling system. When refilling the radiator did you have the bleed screw next to the cap open? Bentley says to open this and slowly fill until coolant with no bubbles comes out the bleed screw. While filling you should also squeeze the radiator hoses to displace air in the hoses with coolant. Just changed the t-stat on my '93 325 and the procedure worked fine. I was warned before I did it that removing air from the system can be problematic. Good luck!

Hi
Thanks for the reply.

I did bleed the entire system, the bleeding screw on top of t-stat, the bleeding screw of the radiator and the bleeding screw on the engine block......
none of them worked.. :banghead:

when i started up the car with the fill cap open, i can see gush of bubbles bubbling out......

Can you explain, "...none of them worked."
When you refill the coolant system the block DRAIN screw should be closed. I don't recall an external bleed port on the thermostat housing (there is an air bleed hole in the thermostat itself, but if the t-stat wasn't removed it should still be positioned correctly--bleed hole due north). The only open BLEED screw should be the one on the top of the radiator next to your recovery bottle. My concern is whether you placed the heater control unit in the full "HEAT" position or not. Remember, by changing the HCV you drained a portion of the heater core. And to refill it, you need to be in the heat position. I would recommend topping off the coolant again and drive and watch coolant gauge.
Also, verify that your cooling fan comes on 1) when you activate your AC and 2)when the temp gauge is just above half way. The cooling fan, if I'm not mistaken, on your year M42 is responsible for heat dissipation from the radiator and the condenser.

sorry for the confusing statement.
What i meant was i did the proper flusing procedure by opening all the bleeding screws when flushing the coolant out. When refilling the coolant, i closed all the bleeding screws except the one on top of the radiator.

I did turn the heater to its max, and there is heater in the car and very strong too. The temperature gauge remains at the half way mark until i turned off the heater and turned on the AC, thats when the car starts to heat up, also i noticed the AC fan is on when i turned on the AC...

very strange...

perhaps to explain the engine heating up you need ot understand what the heating and air conditioning systems are....it's in essence a heat exchanger, the airflowing over metal foils cunducts heat away from the engine and pumps the heated air into the passenger compartment, this helps cool the engine...it's also why you turn the heat on full blast when you overheat your engine...the air conditioning works in reverse...it uses a special chemical underpressue to radiate heat (created during compression) and then it expands to a much cooler temperature which once again is conducted to the air through metal foils.
The problem you probably have in either an undersized rad or a serious problem with your oil....if you've already flushed everything....check the engine for abnormal wear patterns...

i had this problem before, it took me a while to figure out what the problem was.

I first thought that the overheating was due to the lack of coolant. I flushed the coolant, and replaced it with fresh coolant, and my OBC said to check the coolant level. I then bought a new coolant sensor, and had that installed. that was not the problem.

The second thing that I did was check the thermostat, I replaced it. it took a while because we had to remove the fan clutch and the thermostat housing. After we replaced that, it wasnt the problem.

The third thing was the fan clutch. It was part of the problem, but not the main problem, it was still overheating, but not as bad as when it didnt have coolant in my car.

The last thing that I did was replace the radiator, and bingo! after that, with the new coolant sensor, new coolant, new thermostat, and new fan clutch, my car stopped overheating, the entire process for figuring all of that out took 2 weeks. I even bled the system before flushing the coolant.

You could be having the same problem, check the fan clutch, and the radiator, you might have to replace both. getting to the fan clutch is no problem because its inbetween the thermostat housing and the radiator, the only problem is putting the timing chain back on the pullies.

Hi thanks for all the help.

I took the car down to a mechanic today and they said the situation is not looking healthy...

He told me it has got nothing to do with the radiator or the coolants but suspect a head gasket failure.... how much do u guys think it will cost to replace this item.... is it going to be a big job on BMW??

Ouch! Depends on if you just need a new gasket or a new head (warped or cracked beyond repair). I've seen $1200 and up (mostly labor costs).