1991 318is Cooling Issues

[monty23psk]

Yes, it is the cap. Replace the screw. Hopefully the threads are ok. If they are not, you have the option of adding a brass screw that will re-thread the threads. If that doesnt help, then you need to replace the plastic piece or radiator.

The heater core is in the car under the dash. Nothing to do with radiator. The hoses that lead to and from the heater core are on the firewall, back of engine. Search on checking your heater valve. If your heater valve is ok and still no heat, then you could have a clog inside the core or the hoses leading to and from the heater core.

[BobbyZ]

I will try sealing the bleeder screw more effectively.

Feeling the hoses that go to the heater core inside the engine compartment, only one of them is hot. The other one is completely cool, could this difference in temperature be caused by a clog in the radiator that is not allowing fluid to get to the back of the engine?

[Mike325]

I still think that you are not getting great flow through the radiator, as you stated that the bottom hose out of the radiator was cooler than the top one after some time and the thermostat should have opened.

When you said it was cooler, by how much so? Like considerably cooler or just like a tiny bit. Also, if you were not getting good flow throughout the cooling system, such as a blocked radiator, the heater would not get a good supply of hot coolant to give heat in the car.

What is the condition of the radiator's exterior? Does it look like it has been damaged in any way? Was the coolant that you drained out the first time all rusty colored?

[Mike325]

I will try sealing the bleeder screw more effectively.

Feeling the hoses that go to the heater core inside the engine compartment, only one of them is hot. The other one is completely cool, could this difference in temperature be caused by a clog in the radiator that is not allowing fluid to get to the back of the engine?

Just saw this after I posted. Which one is cold? Something is not letting coolant flow freely, we just don't know where yet.

[BobbyZ]

I don't even have the thermostat installed so that should be a non-issue.

The radiator looks to be in very good shape. There is no obvious damage that would indicate a problem, but that was the next thing I was going to try.

[BobbyZ]

Just saw this after I posted. Which one is cold? Something is not letting coolant flow freely, we just don't know where yet.

I actually went under the dash so I could be sure. I think the one that goes to the valve is cold. The other on is hot.

[Mike325]

Use these images to help us help out.







Check your oil too. Does it look milky? Just ruling out a head problem too.

[BobbyZ]

So the hose that goes through the heater valve to the core (part 7 in the first picture) is completely cold. The other one (part 13) is very hot.

What is part #4 in the second picture?

I haven't checked the oil yet but if a blown head-gasket is causing the car to overheat isn't it because of coolant loss? I am standing there keeping the coolant at the right level while it overheats.

[Mike325]

A warped head could cause overheating yes. I would double check your oil to make sure it is ok.

I would start at the inlet hose to the heater core that you said was cold and start to feel backwards towards the front of the car and make note of any temperature changes. If it does not get hot by the time you have traced back to the radiator, I would say that the radiator is not letting coolant flow. The hoses that go to the top of the radiator is hot right? But the bottom or exit hoses from the radiator are cold?

[monty23psk]

Regarding the heater core, one should always be hot. The other will be cold as it will only get hot after coolant has gone through the heater core. I believe you valve is broken and when they break, they stay closed. So you wont get coolant into the heater core and then out the other hose. Coolant is pretty much flowing in one way on the car.

After the bleeding how is the temp gauge? You havent stated.

[BobbyZ]

OK, well now after bleeding for the third time I finally got heat in the cabin and the temperature seemed to stabilize. It looked like it was going to be fine so I let it run for about 45 minutes. Eventually it overheated again.

I think that this may all be due to the leak in the bleeder screw. It may be letting air in which is keeping me from maintaining good circulation. I am going to try repairing what looks like a crack in the plastic near the screw.

[monty23psk]

It is possible that some air is in the system but it shouldnt be enough to overheat the engine. You might have a blockage. How high does the needle go? Also how hot is it outside when you bleed it?

[BobbyZ]

I have only been doing this work at night so it has been pretty cold outside. ~50 degrees

[monty23psk]

Then if you still overheat, then its air or blockage, or bad pump. You have the tstat out so that can't be it. Also if after 30 mins it goes, then maybe the fan clutch is bad.

[jeff_b]

I have only been doing this work at night so it has been pretty cold outside. ~50 degrees

Pretty cold, fiddy degrees. You make me chortle.