partial cooling system overhaul, temp issues and lower hose cold

[Taymar]

I'm hoping I can get some advice on this for a friend please. The car in question is a 96 318ti, with 67,000 miles.

It was due for a coolant change, and also had signs that coolant had been leaking slowly from around the thermostat housing and the pipes that run to the heater core. Temperature gauge was reading low when driving, and reading just above the middle when in traffic. It used to always read right in the middle no matter what.

The coolant was drained including the block drain plug, new thermostat & housing were fitted, and new pipes were fitted that link up the heater core.

The bleed screw and (integrated) expansion tank cap were removed, heater set to max heat and fan set to low, and the car was filled with coolant, with the front end higher than the rear. it was filled until solid coolant started coming out the bleed screw hole, then the bleed screw and cap were refitted.

The car was then bled again with the engine running, using a modified bleed screw with a hose that routes back into the expansion tank (to catch the ejected coolant). The radiator hoses were both soft at this point and were massaged to help remove some air from the system.

It's been bled at least three times total during this repair now.

Now the car seems to read a little hotter than usual on the temp gauge (just above middle), and the upper radiator hose gets hot and solid while the lower one stays cold and squeezable.

When the engine is running with the bleed screw opened (modified bleed screw routing coolant back into the expansion tank, with a constant stream of coolant) and the expansion tank cap off, the lower radiator hose gets warm and the top hose was hot but still soft enough to squeeze.

This doesn't seem normal that the lower hose should stay completely cold when the system is closed, but I could be wrong.

Any advice or suggestions would be much appreciated.

[cooljess76]

Sounds like there's still an air bubble or something preventing coolant from circulating through the radiator. Did you remove the water pump? I've heard of water pumps fitted with plastic impellars failing and clogging the radiator with bits of plastic. It's also possible that you may have a defective or wrong temp thermostat. Are you getting hot air from the heater?

[Taymar]

Thanks very much for the reply. The water pump wasn't removed. The new thermostat/housing was not a genuine BMW part, it was a Vernet-Calorstat piece P.N 176BM0130 (for M44 engine).

The heater is blowing very hot, hotter than it used to.

[sunbrn]

Originally Posted by Taymar

Thanks very much for the reply. The water pump wasn't removed. The new thermostat/housing was not a genuine BMW part, it was a Vernet-Calorstat piece P.N 176BM0130 (for M44 engine).

How much did you pay for the non oem BMW part?

[Taymar]

I believe it was £27.75 from GSF car parts in the UK.

[marc]

Air bubbles in this engine are not usually a problem. Look for a partially clogged radiator, very hot water going in, very cold going out. One of those neat no contact themometers is also nice to see this you can measure different spots on the radiator. The electric only fan is also a problem (burned out). Check voltage while the engine is hot. Voltage and no operation = bad fan. The post on the water pump is helpful also I have seen many impellers break in various places and ways. Be careful removing the WP they can stick in the block and break off the removal tabs. Motors can go into meltdown easily when run hot. Compression check and leakdown test will show.

(BMW master tech)

[dave45056]

You can also give bleeding another try. I find that parking on an incline (front of car higher than the rear) helps alot.