Overheating Problem Need Advice

[anaksarawak]

Understanding the cooling system:
• The waterpump (centrifugal type) is driven by a belt. It allows the coolant to circulate.
• The thermostat controls the coolant flow into the radiator. Closed when the engine is cold (nothing goes in the radiator, open when the engine gets warm to flow the coolant inside the radiator and cool it down.
• The primary coolant fan is mounted to the front of the waterpump with the fan clutch.
• The fan clutch is a viscous fluid type that control the speed of the fan based on engine compartment.
• A two speed auxiliary cooling fan is mounted in front of the condenser. It is uses when the A/C operates and when coolant temperature exceeds 196F (91C)
• The fan shroud is also an important item not to overlook: the presence of a shroud, with about 1/2" to 3/4" clearance between the tips of the fan blades & the shroud opening, and the fan inserted about 1/2 way into the shroud opening is essential for efficient cooling performance.

First: make sure that your radiator is in good condition, check the belts, the hoses and the coolant level. Make sure that there is no coolant leaks. Check the condition of the shroud for cracks & its proper installation.

Car fluid or coolant circuit element just changed:
Your overheating is probably due to air trapped into the coolant circuit. Use the bleed screw to bleed the circuit. Then bleed again, again, again and again.

Nothing had been changed, car is overheating while idling or heavy traffic:
1. Check that the thermostat works and opens.
2. Check the fan clutch.


Car overheating while driving. Not stop and go.
1. Bleed the cooling circuit.
2. Check the thermostat.
3. Check the water pump.
4. On the 535i, check the bypass hose located and attached just above the upper hose neck on radiator and runs along the inner walls to the Resivior tank. If it is plugged, the car will overheat.


Overheating with A/C on, or very high temperature only.
1. Check that the auxiliary fan is working properly(Bentley manual page 170-4).
2. Check the fan clutch.

How to check the thermostat:
A slow working thermostat is hard to diagnose. When the engine is warming up and the temperature needle is near center, touch the top radiator hose. If hot, the thermostat is working (could still be a slow one). If there is cold area in the hose or radiator, check the thermostat.

How to test the fan clutch:
Sorry guys, the newspaper test is not reliable. If the thermostat doesn't work or is slow moving, the fan clutch will fail the newspaper test and will spin freely don't even bother explaining how it is done as it is dangerous.
What you should do:
1) make sure that the thermostat is working!
2) when the car is cold, the fan clutch should turn with a small resistance and not spin freely.
3) Let the car idling and the hood not closed but down. After 5-10 min, the temperature will rise at the 1/2 mark, check that the fan is blowing a LOT of air inside the engine compartment and increase in noise level, no need to put your hands, you will feel it. If when the temperature hits the 3/4 mark, the fan is not blowing a lot of air, that means that: either the thermostat is not working or slow, or the fan clutch is bad.


Bypass hose modification: (Thanks to Dave Smith) Picture from Gale
Dave enlarged the hole on the end of the pipe from the radiator to the expansion tank.

The pipe that runs from the radiator to the expansion tank is about 1/4 inch diameter (internal) , but just as it enters the expansion tank it reduces in size down to 1/64 inch diameter. this pin hole is what was blocking and causing overheating... I have enlarged the hole by running a 1/4 drill down the pipe and this should prevent any futher blockage.

 

[tc@torpedo]

Thanks a lot Geoffrey!

 

[VNP]

Understanding the cooling system:
• The waterpump (centrifugal type) is driven by a belt. It allows the coolant to circulate.
• The thermostat controls the coolant flow into the radiator. Closed when the engine is cold (nothing goes in the radiator, open when the engine gets warm to flow the coolant inside the radiator and cool it down.
• The primary coolant fan is mounted to the front of the waterpump with the fan clutch.
• The fan clutch is a viscous fluid type that control the speed of the fan based on engine compartment.
• A two speed auxiliary cooling fan is mounted in front of the condenser. It is uses when the A/C operates and when coolant temperature exceeds 196F (91C)
• The fan shroud is also an important item not to overlook: the presence of a shroud, with about 1/2" to 3/4" clearance between the tips of the fan blades & the shroud opening, and the fan inserted about 1/2 way into the shroud opening is essential for efficient cooling performance.

First: make sure that your radiator is in good condition, check the belts, the hoses and the coolant level. Make sure that there is no coolant leaks. Check the condition of the shroud for cracks & its proper installation.

Car fluid or coolant circuit element just changed:
Your overheating is probably due to air trapped into the coolant circuit. Use the bleed screw to bleed the circuit. Then bleed again, again, again and again.

Nothing had been changed, car is overheating while idling or heavy traffic:
1. Check that the thermostat works and opens.
2. Check the fan clutch.


Car overheating while driving. Not stop and go.
1. Bleed the cooling circuit.
2. Check the thermostat.
3. Check the water pump.
4. On the 535i, check the bypass hose located and attached just above the upper hose neck on radiator and runs along the inner walls to the Resivior tank. If it is plugged, the car will overheat.


Overheating with A/C on, or very high temperature only.
1. Check that the auxiliary fan is working properly(Bentley manual page 170-4).
2. Check the fan clutch.

How to check the thermostat:
A slow working thermostat is hard to diagnose. When the engine is warming up and the temperature needle is near center, touch the top radiator hose. If hot, the thermostat is working (could still be a slow one). If there is cold area in the hose or radiator, check the thermostat.

How to test the fan clutch:
Sorry guys, the newspaper test is not reliable. If the thermostat doesn't work or is slow moving, the fan clutch will fail the newspaper test and will spin freely don't even bother explaining how it is done as it is dangerous.
What you should do:
1) make sure that the thermostat is working!
2) when the car is cold, the fan clutch should turn with a small resistance and not spin freely.
3) Let the car idling and the hood not closed but down. After 5-10 min, the temperature will rise at the 1/2 mark, check that the fan is blowing a LOT of air inside the engine compartment and increase in noise level, no need to put your hands, you will feel it. If when the temperature hits the 3/4 mark, the fan is not blowing a lot of air, that means that: either the thermostat is not working or slow, or the fan clutch is bad.


Bypass hose modification: (Thanks to Dave Smith) Picture from Gale
Dave enlarged the hole on the end of the pipe from the radiator to the expansion tank.

The pipe that runs from the radiator to the expansion tank is about 1/4 inch diameter (internal) , but just as it enters the expansion tank it reduces in size down to 1/64 inch diameter. this pin hole is what was blocking and causing overheating... I have enlarged the hole by running a 1/4 drill down the pipe and this should prevent any futher blockage.

Thanks Geoff for the detailed explaination on the workings of the cooling system. But how do you explain that when the thermostat is taken out, just for tesing purpose by the mechanic, the temperature went way up? After that put back the thermostat and the temp. is back to normal - middle mark.

 

[anaksarawak]

VNP,

The infor are what I got from the net.. You may try visit my trusted workshop at USJ,

For those with a GPS N 03 ۫04.054` E101۫36.104` (garmin format)

 

[zidee]

Hi,

I'm about to decide to get a year 2000 E39 525 with M54B25 engine. Loan approved but before I finalise the purchase i decided to take the car to mechanic to do diagnostic check. After the diagnostic only one error discovered. Parking Distance sensor not working (can it be easily repaired?). Anyway that does not deprive me from taking this car. However on the way back from workshop, during heavy rain and jam, the temperature shoot up to 3/4.When cruising, temperature back to normal. When rev the engine high in neutral gear, temperature back to normal (half). When idling or stop temperature back to 3/4 and at one time almost hit the red zone.

This really scares me as I've gone through radiator lower hose burst before on my previous E34 during traffic jam. Even after fixing the problem, radiator have to top up from time to time. I decided to let go the car.

My worst nightmare is head gasket crack.

What could go wrong?

Fan clutch? I notice aircond takes time to cold when start the engine. Salesman said this is normal for BMW. Is it so?

How about water pump? Is it not working properly that cause the problem?

Salesman said he will fix all those problem. I told him after all the fix, I want to do compression test to make sure head gasket not warp or crack. Where can I do compression test? How much will it cost should engine require top overhaul?

Final question....should I walk away from this car. Such a beautiful machine to drive with very responsive throttle and comfortable.

Appreciate any advise.

 

[AZM]

Hi,

However on the way back from workshop, during heavy rain and jam, the temperature shoot up to 3/4.When cruising, temperature back to normal. When rev the engine high in neutral gear, temperature back to normal (half). When idling or stop temperature back to 3/4 and at one time almost hit the red zone.

.

Similar symptoms happen to me as well last few weeks. Turn out that the Auxillary fan not working properly. Replaced with a used unit sourced from chop shop. everything went back to normal.

 

[Hammer278]

Interesting thread..many E34s with issues here. Mine isn't perfect either, have to top up radiator around 1/4 litre once a month or so. Have sent to mechanic and he can't find any problem anywhere. Did pressure test, checked hoses, thermostat, fan everything working fine. Even he says it's a mysterious leakage. But since it's not much of a hassle right now I'm leaving it be.