Coolant System Overhaul Preparations

Helena tried to over heat the other day while stuck in a drive-thru. I'm sitting there one minute, I'm looking at the needle rise the next. As it would seem when I opened up the heat, the system was improperly bleed. This lead to a big ole air pocket getting stuck in the system. These models are exceptionally effected by having air in the system.

Upon further research I discovered that the system is pressurized up to 2 bar (29PSI). The Bahr overflow tanks can explode under such pressures. Albeit rare, sometimes they do. I'm wondering if there is a benefit to such pressure. The higher the pressure the higher the temp of the coolant before it starts to boil. Most vehicles run between 15 and 18 PSI. There is one company German Auto Solutions, providing overflow tank caps that put the system at 1.2 bar (17psi). BMW seems to have understood this as well. Newer models come with a lower pressure rating now. I'm interested in this. More later.

Helena has a mechanical fan fan clutch. These can also fail over time. Sometimes they stop spinning altogether. Other times they lock up and do not variate with engine speed. This leads to the fan exploding. Note: This statement may be a myth. Per better sources: Most people do not replace their serpentine belt tensioner and the belt lets loose, that then in turn causes the fan to fail. I've also heard of cheap replacement fans throwing their blades at higher RPMs.

When the fan fails the radiator, overflow tank, hoses, pulleys, belts, and thermostat can be adversely affected by flying pieces of broken components. The pulleys are also made of plastic. The radiator fan is, of course, made of plastic as well. There are euro counter parts available that have a plastic ring surrounding the blades. This helps with this issue. Giving the blades a bit more rigidity. If this fan was to explode it would cost quite a bit more than the stock fan and clutch, that's for sure.

She also has an auxiliary fan mounted in front of the radiator. This is operated by a aux fan switch that should come on when the coolant reaches 91°-99° C. This fan also comes on and off when the A/C is running. So in essence the radiator has a fan that pushes air from the front (aux fan) and pulls air from behind (mechanical fan).

I was told when I bought it that some work had been done to the coolant system. No paper records but, there is an aluminum thermostat housing on this car. That means it had been replaced from the plastic composite one that would be there normally. It has 05/15 etched in to it. The hoses appear to be newer as well. I'm guessing they were changed at the same time. Or at least not swollen and nasty. 

This is good and bad because I have no idea about any of the other pieces in the system. Has the water pump been changed? How old is everything else? This 328 has 160K on the clock. Just a matter of time before stuff goes wrong if I don't do some preventive maintenance.

Which is what has lead me to where I am now. For my piece of mind, I need to know that the coolant system is in good order. So, off to the parts websites to order what I think I need.

Here is the lot of stuff I got:

- Coolant Overflow Tank (BMW)
- Coolant Level Sensor (FEBI)
- Upper Radiator Hose (GATES)
- 92`C Thermostat (BEHR)
- Water Pump (GRAF)
- Water Pump Pulley (ECS)
- Water Pump Nut (BMW)
- 80/88 Aux fan Switch (URO)

What I already had

- Aluminum Thermostat Housing
- Fan Clutch
- Fan
- Belt

- Lower Hose looked good.
- Overflow to Heater core hose looked good.
- Upper Overflow hose looked good.
- Radiator looks like it has been replaced as well.

  The folks who did the coolant system changes before didn't do half bad a job. This car has obviously had green coolant run in it for quite some time. my overflow looks like a ninja turtle.

  The original issue of overheating was taken care of by bleeding off the system properly. Which thanks to my friend Jeremy, is made a lot easier by jacking up the front of the car. Following the standard BMW coolant change procedure, when jacked up in such a fashion, the air bubbles rise up front faster and easier. Nice!

  Well if the car isn't overheating anymore why buy stuff? While working out the overheating and checking the other components of the system, I discovered that the fan came in contact with the upper radiator hose at some time. There was a small divot taken out of the hose down to the braiding. This made me nervous. If I am going to take the hose off then, I might as well replace some of the other components as well. 

  Again, I need piece of mind in regards to the age of the components. Preventive maintenance, mixed with a little performance maintenance. More to come on that.