I am still experiencing a cooling system leak on my 1993 940 non-turbo with automatic trans. The hose clamps are tight and a new heater hose is installed. There is a sensor at the front of the transmission at the top which is right next to the pipe from the water pump. I noticed that the insulation on the cable for this sensor appears to have been somewhat melted away presumably from hot coolant spraying on it. Is there any coolant in the transmission by this sensor? I am thinking that perhaps the sensor may have been cracked or is just worn out and maybe coolant is actually coming out through this sensor thus burning the insulation away some in the process. Someone mentioned in another thread that this might be the crank position sensor if it is any help. This is a very baffling problem since the leak only appears to occur while driving the car resulting in coolant leaking all over the exhaust pipe creating a cloud of steam from under the hood. Pressure tests have not found any leaks that might be causing the problem.

That is not a sensor that has any connection to the car's cooling system. If it comes directly out of the top of the transmission immediately behind the engine it is the crank position sensor aka rpm sensor.

If the insulation on that sensor/wire is coming loose you are simply running on borrowed time. Bad insulation is the first indicator that it needs to be replaced before the second indication steps up: a no start situation.

The pressure in the cooling system is actually higher about 5 minutes after shutting the engine down after a spirited drive. Heat builds up after shutting the engine down and pressure increases.

Shut the engine off and wipe down the area around the suspected leak. After a few minutes use a strong light and survey the area to locate the leak. Chances are from the description you give it will be one of the heater hoses or the heater control valve.

Good luck,
Randy

I am waiting to find the leak before I replace the timing sensor since it appears that hot coolant has been spraying on the sensor cable. I don't want to replace the sensor just to have the hot coolant spraying on the new one before I find the leak.

Hello,


Instead of speculating, which can be helpful, right now you need to warm the engine up and LOOK for a pinhole hose leak. They can be hard to spot; I know from experience that they are tricky to find in the first place, and nearly impossible with the engine off.

Raise the car on jackstands and start the engine and idle it until it starts leaking. Then, using your flashlight, look for the stream.


Goatman

Like I said it only happens while driving the car so I can't very well have the car on jack stands and in gear.

He's right. There's only one SIMPLE way to discover where its leaking, look. Waste a can of brake clean in that area first to clean it off well. Take it for a 10 minute burn. Return to driveway and really get under there and look. That being said you could buy a pressure test kit or go and pay a shop to pressure test. But that will cost ya.

I have had the system pressure tested twice with inconclusive results. The only leak was a very minor leak at the bottom of the radiator which would not be causing the clouds of steam that come from coolant in contact with the exhaust pipe after it comes out of the manifold. there is obvious coolant in the same area on the framework at the rear of the engine compartment. when I open the hood the most I see is a the steam coming off the exhaust pipe but the car is not in gear then. It does not seem to be a constant leak but only intermittent when the car is in gear. It does not occur every time I drive the car either. I am basically looking for other ideas or possible ways to check it. I had a couple of other small leaks that I have resolved such as the thermostat housing leaking. For that I placed chalk marks on the engine block and just below the thermostat housing and confirmed the leak. The leak I am still having problems with is more difficult to locate. I am considering getting some powdered chalk and just covering the area at the rear of the engine block to see what might be revealed if I can't find any other suggestions. The chalk would be washed away by the coolant.

OK I have a better picture of whats going on. Is there any correlation between the leak and when you have the heat on or off? Just thinking that there is the "pre-heater tube that goes from back of water pump along the block to the back of block. Its not unheard of for that tube to rust out at the point where it is affixed to the block by a clip....just thinkin aloud.

I do not think it matters much if the heat is on or off. I think I have seen the problem both ways. I did get some powdered chalk to used to help me pinpoint the problem and will be placing it around the area I suspect is leaking. It does seem to be more prevalent when the temperatures are colder though so it is mostly when the heat is on from that standpoint, but maybe it is when it is colder that the steam cloud is also more visible. Is is possible that a freeze plug might be leaking?

Dear MadDogKY,

Hope you're well. To help find the leak, see if you can slide over the water pump's rear coolant, pipe, a sleeve of white paper towel. Tape it into place. Bring the engine up to operating temperature. If there's a pin-hole leak in that pipe, coolant will wet the paper towel and change its color from white to pale green. The advantage of using paper towel, is that any escaping coolant must hit the towel as soon as it exits the pipe.

If you can get the paper towel around the pipe, use aluminum foil over the paper towel, to hold the paper towel into place.

Hope this helps.

Yours faithfully,

Spook

I found the leak. There is a cooling system drain plug on the block right near the 4th cylinder on the right side of the block. Somehow this has come loose and is spraying coolant onto the exhaust pipe resulting in a cloud of steam. It was not easy to spot but with the help of a friend with better eyesight we found it. A new plug has been ordered since just tightening it only helped for a couple of days.