Van has one installed, was done by a previous owner, so don't know much about its install. Was working okay when I first got the van in September 2020, but the coolant was in very poor condition. Drained, flushed and refilled the coolant with red antifreeze, Triple QX and changed tank screw, thermostat, water pump, cleaned header tank and fitted Rusty's bleed kit at the same time. Within a week of running it, the alarm came on, as expected with fresh coolant. Took screw out again and cleaned it, made it go quiet for another week. Done that numerous times until it now makes no difference.
A couple of months on, the coolant alarm stays on when van first started, if you rev the engine it will go off, but then come back on when idling again. It's like that until fully warmed. Now it is even worse. Sometimes comes on when fully warm and driving along.
If it comes on when warm and driving along, if you turn on the rear heated window it goes off, for about 5 seconds then comes back on. You can do that repeatedly. If fully warm and driving along and the alarm is not on, I can make it come on by using the windscreen washers!
It goes without saying the level is fine, and the screw is clean. I have done some tests now, all with ignition on but engine off. I can confirm that:
The alarm does not go off:
- After the self test
- If I add a jump lead from the block/head direct to the battery
- Earth the screw direct to the battery
- Earth the water in the tank direct to the battery
- Earth the water in the tank to the engine block/head
- Earth the water in the tank to any exposed metal part on the car
Could it be the coolant has lined the inside of the engine so well the circuit won't complete??
Fresh out of ideas here, help please!