radiator losing water/coolant!

hi everyone, i am new to bimmerfest and this is my first post. i hope some one can help me with this issue i have with my bmw 316i se.

my radiator needs topping up with water/coolant roughly an hour or less into driving the car. i have had the radiator, electric fan, fan resister and thermostat changed so far. i have recently had an oil change and have also changed the coolant fluid and have not had any indication that the head gasket is leaking.

for some reason my coolant heats up very fast within 5-10mins and the temp gauge goes up, two thirds of the way towards red and only then does the electric fan kick in. the temp gauge seems to stay two thirds of the way towards red...

i have had a mechanic have a look at this problem but he can not find any leak anywhere.

so can someone please help me figure this out. i can't get my head around how the radiator is losing this water/coolant and why it needs topping up within an hour or so in to driving and also why the coolant temp goes all the way up, two thirds towards red before the fan kicks in.

thanks in advance

You didn't replace your water pump?

Something is being affected by the temperature or a pressure buildup. Have your mechanic do a cooling system pressure test with the engine at operating temperature. If that doesn't find the cause, have the coolant analyed for combustion gases. That usually indicates a head gasket leak. There are kits available at auto parts stores over here, but I don't really know about your side of the pond. A good mechanic should be familiar with this type of test. It's probably not the radiator but could be the water pump, expansion tank, thermostat, etc. By the way, your 316i is probably a four cylinder. All the E46 models in North America are 6 cylinders. There are some differences.

well i did consider replacing the water pump but it dosnt explain where the water/coolant is disapearing too (theres no water leaking from the water pump and the temp gauge does not go to red). however replacing the water pump might solve the temp gauge issue. thanks

Originally Posted by overheat

well i did consider replacing the water pump but it dosnt explain where the water/coolant is disapearing too (theres no water leaking from the water pump and the temp gauge does not go to red). however replacing the water pump might solve the temp gauge issue. thanks

A small amout of coolant coming from the weep hole on the water pump can evaporate on a hot engine and be very difficult to detect. There usually is some residue though. Look for that.

crack/hole on coolant tank

You have a hole somewhere or one of your hoses are bad try and run the car and see where its coming from.

the car was run for a couple of hours, no steam was detected coming from any of the hoses. theres no steam coming from the radiator either.

catso, i will look for the residue on the water pump. thanks for all your help so far guys!

p.s catso, if there is a small hole in the water pump, would the coolant leak out when the car is stationary and not running, im only asking because i have not noticed any liquid under the car.

Originally Posted by overheat

the car was run for a couple of hours, no steam was detected coming from any of the hoses. theres no steam coming from the radiator either.

catso, i will look for the residue on the water pump. thanks for all your help so far guys!

p.s catso, if there is a small hole in the water pump, would the coolant leak out when the car is stationary and not running, im only asking because i have not noticed any liquid under the car.

That's the "weep" hole. If the bearing or seal is going bad you might be leaking coolant out of there. It could drip out after running for awhile and developing some heat and pressure. Even after the motor is off a small amount might leak out.

right, ill have a look and post the out come. thanks catso

hey guys! i thought id give you an update...my mechanics finally found the problems with my car or so i hope he has! the heater matrix and a plastic pipe at the rear of the engine seems to be leeking. i have bought the parts and they are due to be put on. the mechanics charging me £90 to put the heater matrix and plastic pipe in! ill give you an update once its been put in.

the loss of coolent has stopped, now that the heater matrix and plastic pipe from the rear of the engine has been replaced, however i still have the problem where the fan is only kicking in when the temp gauge reaches two thirds of the way towards red :'(

Originally Posted by overheat

the loss of coolent has stopped, now that the heater matrix and plastic pipe from the rear of the engine has been replaced, however i still have the problem where the fan is only kicking in when the temp gauge reaches two thirds of the way towards red :'(

You'll have to look at the temperature sensors. It might even be a thermostat. Make sure the cooling system was bled properly, it can require two or more attempts to get all the air out. You don't want your engine overheating.

Originally Posted by catso

You'll have to look at the temperature sensors. It might even be a thermostat. Make sure the cooling system was bled properly, it can require two or more attempts to get all the air out. You don't want your engine overheating.

+1 on the thermostat and bleeding the system properly. While you're there, I'd recommend replacing the hoses as well. It took me three times to bleed the cooling system out before it was purged of all the air. A good indication (atleast on the e36's) is the lack of heat in the cabin (heater) when air is trapped in the system. Hang in there!