Question about Heating & Cooling

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I change head cylinder,timingchain,waterpump and it still overheat.it has a 2 speed fan and it does not turn on,only when i turn de air condition.

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  • l_a3720 Jul 08, 2010

    my 1998 bmw 318ti it has two speed one to cool the engine and the other speed for the air condition. the fan speed for cooling the motor those not turn on.only the air condition speed turn on.

  • l_a3720 Jul 08, 2010

    i have a 1998 bmw 318ti i change the cylinder head,timingbelt,waterpump,and when i turn on the car it was heating.so i change the radiator fan swicth because the fan to cool the motor was not turning on.the car has a two speed original fan but it only turn on with the air condition.it does"nt want to turn on to cool the motor.

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3 Answers

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  • Master
  • 6,826 Answers

So, if you turn the a/c on the fan works but otherwise the coolant temperature sending unit does not turn on the fan for hot coolant conditions?

I would look for a fusible link that supplies the fan for normal cooling without the a/c on.

It's common for technicians to neglect to find the broken fusible links in the wiring harness near the starter of GM cars, anyway.

Stretching the insulation reveals a broken fusible link wire inside the casing. Try to find it that way.

Posted on Jul 08, 2010

  • l_a3720 Jul 08, 2010

    i check power in the wire that connects to the fan plug there is power going thru.

  • Duane Wong
    Duane Wong Jul 08, 2010

    If you have power there, I am not sure why it would overheat then, unless there is a restriction in the passages or a miscalibrated sending unit.

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  • Master
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If relay and fuse is good, check coolant temp. sensor, will sit on thermostat housing or very close to it, will have two wire connector, disconnect it, if fan come's on, bad sensor, replace it. Also by disconnecting the sensor after repair's have been done the computer will have to be reset, disconnect battery for about 15 sec to reset computer.

Posted on Jul 08, 2010

  • l_a3720 Jul 08, 2010

    i replace the radiator fan swicth and it still does"nt turn on.why does the fan turn on only whit the air condition.

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  • Master
  • 905 Answers

You didn't mention if the fan was original equipment or aftermarket or not, so will assume both scenarios.

Both:
AC turning the fan on via a relay is a good sign. It indicates that the fan is working and not suspect. The fan relay will be in parallel with thermostat relay. AC relay will likely interrupt the low speed line, and close the high speed line.

OEM:
Check your relays in the relay/fuse box under the hood. Also check your fuses here as well. You will have to obtain a wiring diagram to see if the thermostat of the fan works off the sending unit that also drives the light / guage on the dash. If separate, then replace sending unit for the fan if relay checks out.

Aftermarket:
Your sender / sensor is likely placed in front of the radiator, zip tied more than likely. Using manufacturer manual, manually trip the sender / tstat assembly (usually involves hot water bath, warm water bath, cold water bath) to try and test the sending unit. It it checks out, then direct your attention to the thermostat itself, and/or the relay that it drives.

Posted on Jul 08, 2010

  • l_a3720 Jul 08, 2010

    whey does the radiator fan only turn on whit the air condition.and it not turning on when the motor is hot.

  • Sheldon Dedek Jul 08, 2010

    Start with a wiring diagram for your car. Find the cooling fan motor, follow wiring backwards. Check the connectors along the way, as well as the relays and fuses as equipped.

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1 Answer

Where is the sensor for regulating the temperature R


There is no electronic coolant temp regulator. That is what the thermostat is for as it regulates the flow of coolant between the engine and radiator by opening and closing based on coolant temp. It is mechanical in operation and operates independently of everything else. If it is faulty and is stuck closed or partly closed you will get an overheat condition.

If you still have an overheating problem after what has been done then it could be due to one of these factors if all else is ok...

1. Air remaining in the cooling system retarding coolant flow. It is imperative that all air is bled from the cooling system or you will get an overheat condition cause by air blocks. If you still see bubbles appearing in the coolant this is an indication that there is still air in the system or you may have the issue described in 3. Manufacturer procedures need to be followed for effective air bleeding of the cooling system after radiator coolant has been changed.

2. A partial blockage in the radiator or in the engine retarding coolant flow due to a build up of debris.

3. Combustion gasses leaking into the cooling system via a failed head gasket will cause an overheat condition. This will show up as bubbles in the coolant when the engine is running and can be checked by doing a leak down test on each cylinder. You might also have some coolant escaping into the cylinders and white exhaust emissions can be an indication of this. If you have been running the engine in an overheated condition this can very easily cause a head gasket to fail and a cylinder head to warp or even crack.



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