Coolant Leak Sensor: Troubleshooting & Repair

Hi!

After a slightly faster drive on the highway, the 'mouse cinema' (infotainment system) in my AJM displayed a message just before reaching my usual parking spot: 'STOP! Check coolant!' (or something similar). I followed the AI's advice and discovered that most of the coolant was stuck to the rear splash guard, or it was pooling in the tray directly below the coolant reservoir. Apparently, too much pressure had built up somehow, and the fluid was released through a relief valve or similar mechanism. I had encountered this problem once before, and the solution was a faulty sensor/sender that controls the switch between the small and large control loops.

Where is this sensor/transmitter located?

Is an error entry stored in memory?

Is there another potential source of error that could be responsible?

Thank you for your help.

Okay, today I drove home from work in 'eco' mode = 120 km/h on the highway, 90 km/h on country roads. And of course, right away, the dashboard displayed the message 'Check coolant level!'. Again, just a few kilometers before my house. I haven't checked yet, but I think the engine compartment will show the same picture as yesterday.

What can you say about that?!

How about a search function and a detailed product description?

Best regards, Rainer.

I've searched, but I couldn't find a similar problem to mine. The issue is that when the coolant level is reported as low, the two contacts no longer reach into the coolant reservoir, and according to the markings, the level is about 1cm below the MIN mark. However, if I open the coolant reservoir cap, the coolant level rises with a hiss to 0.5cm above the MAX mark. So where did all that coolant go in the meantime?

It doesn't appear that there is any oil present in the liquid.

Try changing the fill cap on the expansion tank. The valve inside might be defective and not opening properly, causing excessive pressure to build up. This would cause all the hoses to expand, allowing more water to enter. When the system is opened and the pressure drops, the hoses contract, and the water returns to the expansion tank.

If the pressure is too high and the system has already overheated once, the hoses can expand significantly. This causes water to flow towards them, and when the pressure is released, the water flows back from those hoses into the expansion tank.
"Check ZKD - Search function as previously mentioned."
Replace the lid.
Kühlerlüfter laufen prüfen/ lassen 1.+ 2. StI don't understand. Could you please rephrase?
The engine is overheating, usually only occurring under load and often in the initial stages of the problem.

Thank you for the tips. So, it overheats both during normal driving and under full load. I've now noticed that after 40 km, the upper hose to the radiator is hot, but the lower one is cold (on the right side). This can't be intentional, right? The same goes for the radiator: the top is warm, the bottom is cold.

Then the thermostat is probably defective.
and again: does the fan run when it's cooking, or not?
Does the radiator fan blow hot air when it's overheating?
After driving 40 kilometers, it doesn't mean much; you can also be gentle with the car and keep the interior nice and warm, which means the exterior will stay cold!
But what about the temperature display in the AI system?

In this case, you might be able to save yourself a lot of trouble by checking if there is still pressure in the cooling system after a long cooling-down period (overnight).

If yes --> 99.9% probability of being correct. If not --> continue searching (this has already been mentioned countless times in this forum).

Based on the signature, I'm guessing it's from ZKD. How old is this device?

The car has now been driven for 188,000 km and, until now, without any major repairs. There was always a warm-up phase and a cool-down phase. Today, I replaced the darn thermostat. What a pain with that lower screw. Not to mention the coolant that gushed out. But there's always a first time for everything. So, with the engine running, I added about 2-3 liters of coolant and carefully observed how it was being pumped into the system until no more topping up was necessary.

Test drive, warning message, intense cursing.

@teileklaus
I don't know when the fan last ran. In other words, no. I'm almost certain the fan wasn't running. The temperature gauge in the cockpit is stuck at 90°C. Currently, however, water is being forced into the hoses, which become very hard, causing the liquid level sensors to be exposed to air. Nothing was found on the spray bar during recent trips. The AGB (automatic gearbox) cover is okay. HOWEVER, the lower hose became warm. Perhaps it's just an issue with venting?

@BM
I assume the comment about the SIG regarding ZKD referred to the tuning, right? Yes, that's quite possible. But there were also plenty of unmodified AJMs with the same problem, weren't there?

I'll check the pressure in the system tomorrow morning after the printing process to see if it's still at the desired level.

Quote:

@BM I assume the comment about the SIG regarding ZKD referred to the tuning, right? Yes, that's quite possible. But there were also plenty of unmodified AJMs with the same problem, weren't there?

The AJM engine has the same issues as the other engines, nothing significantly more or less. It's important to know that all 1.9L PD engines (except the ARL) have the same cylinder head and gasket/bolts. Only the material of the engine block differs between the AJM and the 130PS variant in this regard.

Personally, I now consider the cylinder head gasket to be a wear item in diesel engines. And with almost 200,000 km on the clock, that can happen. My AJM engine (the previous owner was known for driving aggressively) already had cylinder head gasket failures at 63,000 km and 142,000 km.

Okay, yes, I'm also getting to know the new ZKD (presumably a piece of equipment). Well, at least the idea of it... are the prices around 500 euros?

Okay, if the thermostat was actually working properly all along – I'm sorry if you broke your fingers. But if you say the radiator isn't getting hot and the fan isn't running...
I'm disassembling almost every thermostat, along with the new one, to see what might have been wrong with the old ones!
Jetzt fülle erstmal auf und dann wird man sehen. Possibly still some room.
Remaining stock will be available tomorrow morning, as mentioned by BM.

Just do a CO test on the exhaust manifold; then you'll know if it's related to the cylinder head gasket.

Okay, the problem car is now at the workshop (with the former friendly dealer) and being inspected. They are checking why the silly fan isn't starting up and, related to that, the overpressure issue in the cooling system. I fear it will turn out to be a blown head gasket, as has already been mentioned several times here.

I will let you know the result when it is finalized.

*sigh* Okay, so it turns out that the CO test suggested by Wingmaster was correct:
Cylinder head is damaged. Okay, there's nothing we can do about it. Last question: Is there anything to consider when installing a new cylinder head gasket, especially if the head needs to be machined for chip tuning? Regarding the potential increase in compression ratio? Or is this negligible?