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E36 General discussion and technical help for (E36) 1992-1999 3 series cars. 318, 323, 325, 328.

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Old 08-05-2011, 06:01 PM   #1
Clyde

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318i E36 cooling problem.

Hi, just stumbled on this forum while searching for a solution to my problem. I have a 1994 318i E36 which up till now has been great. Until today that is. Everything seemed fine until I hit the slip road of a very busy motorway (rush hour, standstill traffic). I was only queuing on the slip road for a few minutes when I noticed a pinking sound, then glanced at the temp gauge and noticed it was approaching the top and the warning light had come on. So, I pulled over, turned off the engine and had a look under the bonnet. There was some steam coming from the filler cap, though there was a good visible coolant level in the tank. I let it cool then squeezed the hoses, the level dropped a little, so I added some water. I repeated this a few times. Anyway didn't want to hit the motorway while traffic was slow so I waited. Then I set off, came off the next exit and took the long way home.

The problem is here, the drive home afterwards was fine, temp stayed at normal all the way, no problems and got home (about 40 miles).

I'm fairly competent with mechanics so I was basically looking for some ideas as to why this would suddenly happen out of the blue. I have noticed now that the heater seems to be blowing cool air even when set to the hot position. I'm wondering if it could be the thermostat. If so, i assume it's stuck open, but why the overheat before that, could it go from being stuck closed to permanently open all of a sudden?

If it's an airlock, why would it just happen out of the blue while driving? If it was the water pump surely the engine would overheat permanently.

There are no visible leaks inside or out, no evidence of steam coming from the exhaust, no water in the oil etc.

Any common failures with this model?. I really need to fix it before I go on another journey.
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Old 08-06-2011, 12:12 PM   #2
Manolito

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On a 325 this age, I would look for a water reservoir that is crumbling inside, causing the cooling system to suck in air. Air might cause overheating at idle but not at higher RPM. The 318 uses a different tank so I don't know whether sucking air is a problem with this tank, but it costs only $20 on line for an OEM tank.

The thermostat may have stuck shut that one time, but generally when a thermostat sticks, it stays stuck.

The electric fan should come on whenever the A/C compressor is running or when the water temperature is high. You can check the function of the water temperature switch, the relays, and the fan by jumping the connections on the plug for the temperature switch that is in the end tank of the radiator. On a car this age, the relay for the low speed of the fan is probably overdue for its first replacement if that has not been done. I replaced the low speed relay in one of my '97s just a few weeks ago.

Check the fan clutch to make sure the fluid has not leaked out of it. You don't want the fan clutch to fail completely and come apart because the fan will chew a hole in the radiator.
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Old 08-06-2011, 02:15 PM   #3
Clyde

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Hi thanks for the reply. It doesn't have A/C and no electric fan, however I will include the fan clutch in areas to investigate.

Checked it today and the coolant level has gone down slightly, leading me to think either there is a small leak I can't see or an air pocket in the system. I might try the bleed procedure but I'm still baffled why it would suddenly need bleeding after 3 years of driving. Other than that I'm just gonna have to take it easy and keep a close eye on the temp.
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Old 08-06-2011, 06:36 PM   #4
Clyde

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By the way it's a 1.8, SOHC M43 engine if that helps with any common faults. Going to take some time and check carefully for leaks. I'm thinking the cool heater is a clue here. Could the core be blocked? It has a permanent antifreeze mixture in all year round, with no corrosion evident. The heater always used to be good.
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Old 08-07-2011, 10:31 AM   #5
3050rpm
 
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Just to add to the list of things that could drive you balmy, you may also wish to check the heater control valve. On the 6 cylinder cars this is located against the firewall in the engine compartment, on the driver's side. Access is absolutely horrible, perhaps better done from underneath if replacement is called for. You will, however, be able to reach underneath it from above with your left hand, so see if it's leaking from cracks or worn hoses. These leaks can otherwise be nearly imperceptible (ask my how I know). If the valve has failed internally that might explain getting cool air even when the heater is set all the way to hot.
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Old 08-07-2011, 12:01 PM   #6
Clyde

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Hi. Well here's the current situation. Decided to try and bleed the system today, loads of air in system. So it's all bled out, now the heater is working fine. Just done a 50+ mile journey with heater on full blast to make sure I had circulation, all the time kept an eye on the temp gauge. No problems at all, gauge varied from the first mark to the dead centre, depending on whether I was motoring or stationary.

So, from that I can assume the thermostat, water pump, radiator and heater matrix are working, also the valve must be working as well.

It is possible that I let the coolant level get too low, allowing air into the system. Every time I had checked the level in the past it had never seemed to move, so I kindof didn't keep an eye on it like I should do.

I could have a leak that is too small to detect at present, I will have to keep a close eye on the level and see how it behaves. I suppose there is also a chance that the head gasket has failed and is weeping water into one of the cylinders, though the engine is running perfectly and the cooling system isn't pressurising.

The car has done over 120K miles so I suppose I should expect things to start failing, I just want to know what has failed/is failing. I'm ok with doing any work that is needed, just want to make sure I don't spend on unnecessary parts.
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Old 08-07-2011, 12:10 PM   #7
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Okay, sounds like good news thus far, but permit a question, has the cooling system been thoroughly flushed, meaning engine block via the drain plug as well as the radiator?
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