Hello everybody,
I'm observing a strange behaviour of the coolant level warning lamp with my 1997 V12 DDS (aka VDP). I think I've read every single post dealing with the coolant level warning, but it seems that none of the cases (stuck float sensor etc.) is applicable.

This is what happens (everything referring to winter temperatures of 0 - 10° C):

• When starting the (cold) engine, everything is OK (i.e. no coolant level warning)
• When running on the highway (@130-150 km/h) everything still is OK (no warning), even if I drive 200 km without stopping.
• When leaving the highway an running smoothly some 5 kms through the city, the coolant level warning comes on (temperature at N)
• When stopping the engine in the garage, the small electric fan will be running for some 5 mins, then stops.

Another scenario:

• Cold engine, coolant level OK, starting engine, no warning, but when running in the city (smoothly), the coolant level warning light comes on after some 20 mins. Checking coolant level -> OK.

When overfilling the coolant reservoir (cold engine) and then running for some time, coolant will come out through the valve in the coolant reservoir cap. I'm not sure whether this is proof enough that there is no other leak in the system.
Even if the temperature gauge is always at N or a littler below, all this makes me think that the warning is temperature-related and has nothing to do with the coolant level. Also, it doesn't seem probable to me the the float sensor gets regularly stuck after driving some 20 minutes.
It seems that Gus from JagRepair found out that the level sensor of his Jaguar has different continuity when the water temperature changes. Even if the expansion tank he is testing is not from a X300 V12 (but from a XK8), this sound like a possible explanation.

Does anybody have an idea what might be going on and how to fix it?
Best regards
Martin

 

Hi Martin,

not sure, but sounds like an electric problem (contact problem, cable break or something like that).
First of all, I would check whether the sensor is pushed-in properly in the coolant reservoir. Then in a second step, I would (with ignition on) slightly jiggle the sensor and then inch along the cable and jiggle again and again and check whether the warning lamp is still on or goes out - for this you need helper of course.
You also can pull out the sensor from the coolant reservoir without any problems, as the sensor is outside the coolant reservoir and thus has no contact with the coolant (no idea how this works, but it definitely does). Maybe you need to replace the sensor.
When I bought my XJ12, it came with leaking water hoses due to a marten, which obviously loved that car... This is why I was concerned with the cooling system, the reservoir, the sensor and all of the hoses and I know for sure that the warning lamp doesnt come before the coolant is VERY low.

Cheers!
Harald

 

Thanks Harald, sounds like a good plan. I don't remember why, but I had in mind that with the 6.0 V12 the expansion tank and the coolant sensor were a unit.
Last time the warning lamp came on, I carefully opened the cap of the coolant reservoir, and it was filled up to the brimming, even pushing out some water. Perhaps the overfilling which is evident and of course gets even worse when the water expands with the heat causes the malfunction of the fluid level sensor, pushing the float out of the measurement range of the sensor. Perhaps this is not even a malfunction, but a feature, i.e. the warning not only gets active when there is a lack of coolant, but also when there is too much of it.
I'll try to clean/flush and refill the system with the correct amount.
Best regards
Martin

 

Hello Martin,
no, its not a unit. I just attach two pics, the one showing the reservoir from the bottom with the sensor standing above the hole to plug it in and the second showing the reservoir sideways with the sensor in the hole. (but not yet in the correct position!). Ensure that the nose on the sensor sits on the little notch and then snap the sensor into place. Thats all.
Best, Harald

 

Have you pressure tested system? V-12s have 2 thermostats as a dual system. Might not be sensor. Have you checked engine temp by way of laser or external temp sensor? Is your coolant cap up to specs (new)? Test it too. If pressure is not maintain in system overheat in spots occurs, not just everywhere, must be careful as not to warp aluminum. Gauge is motor top specific and not reliable for troubleshooting.