I'm helping out a workmate with a 1.4 MPI. He has the coolant level warning appearing randomly and without good cause, and the engine is very slow to warm up. I'm suggesting he replaces the expansion tank (ECP £9-ish? Is that too cheap?) and thermostat. Is it advisable to source a genuine thermostat, or will aftermarket ones tend to be OK? Haven't looked yet to see what prices are like, anyone bought a genuine one recently?

 

Ta.

 

I had an aftermarket thermostat replacement right after I bought the car, back in 2013. It's been working pretty good so far I can say and it still does, with nothing to compain about. I've replaced the expansion tank(6Q0121407B) for about £12, but with a genuine one, there wasn't a big price difference. Have in mind that the new tank will come without the cap (3B0121321) - ~£2, so you might consider ordering it as well, along with the o-ring seal (1H0121687A - not *so* sure) -£1. 

Edited 9 September, 201510 yr by Alexandru

Thanks Alex. 

 

I've actually had a good-value quote for genuine parts via here, which my workmate seems happy with.

I think I have a spare or two of the o-ring you helpfully mention, and your part number seems right.

I just remembered...I've replaced my coolant temp sensor also,  06A919501A, also with an aftermarket one, I think it was ~£15, about 1/2 price of an OEM one. The coolant warning light wasn't on, but sometimes the engine was dying when warm, at idle, due to the too rich fuel mixture. I ran a scan with VCDS and it found it as faulty. I am not sure if this would help in your situation, though.

Edited 9 September, 201510 yr by Alexandru

Thanks again. I think, but am not 100% sure, that the (genuine) thermostat housing assy comes with a new CTS, as well as the thermostat? If it does, that's another bonus of the genuine part (No. 047121111S)

As per here, I'd say you are right, but it would worth asking a question before paying. 

Well the thermostat assembly did indeed come with a new temperature sender. 

The old thermostat seemed to be loose within its housing, as if there was a piece missing, which is strange. Couldn't quite work out which way round the guts of it were meant to sit, but whichever way, there didn't seem to be enough bits in there for it to do its job.

 

Haven't tested much for the level warning light absence yet, but the temperature now goes where it should and stays there.

 

The old coolant tank appears to have oily residue inside it, which may explain the probes not reading the level right?

 

 

Maybe also indicate a HG failure in a PO's time?  It has a Temac gasket on it now, would that have been factory on an 02-plate car, or does that indicate definite replacement?

I would say the engines cooked before yes

Grrrrrrr.

He's still getting the spurious red flashing light.

Wiring? Cluster?

 

Anyone know how it works? DC voltage to the probes and a resistance measurement somewhere in the depths of the instrument cluster? Something else?

Tried bridging the plug on the coolant bottle with a paper clip? If it goes out, the wiring is good. Also, I believe that the wiring can break in the loom, so maybe try a meter on the wiring? Not sure what the voltage should be, possibly 5v?

Thanks fella. Haven't tried anything yet, gonna have a bit of a measure on my Polo in a bit, exactly the same set-up I'm sure. Mine's working fine, so might be a useful comparison.

I'm still none the wiser.

 

On my Polo the voltage at the (unplugged) plug pins seems to vary between 0.3 and 0.35V in a cycle where it ramps slowly (over 20 seconds maybe) up to 0.35, then drops abruptly back to 0.3V, then repeats this cycle endlessly.

 

On his, I measured much/even lower voltages, and no such regular pattern. There was evidence of a bit of coolant in amongst the connector pins, so I'm wondering if the crimp connections where the wires join to the pins may have corroded? With it being coolant though, wouldn't the corrosion inhibitors prevent that? :think:

 

Got a pin extraction tool at home, so we'll maybe have the pins out for a look tomorrow.

I would check for corrosion. I think also that the light doesn't go straight out after bridging the plug, it can take a few ignition cycles iirc from trying to fix mine (needed a coolant flush as it still had oil residue in due to hg failure, which coated the electrodes and prevented reading) so may be worth bridging, cycling ignition a few times, then measuring at the plug again if still no luck.

Glacially slow progress on this.

Last Sunday I think I managed to establish (on my Polo) that a pot set to about 15 kilohms doesn't trigger a low coolant warning when plugged into the connector instead of the expansion tank. Set it to about 60k and the warning does go off; at about 47k it doesn't go off. So the probes need to see a resistance somewhere around 47k or below to keep the alarm circuit from triggering. Yet to validate this on another car. It was a bit fiddly to try to establish anything really accurate as the pot I had was a linear 1 meg pot so I was making teeny adjustments right up at one end of the range.  All this was done with just ignition on, engine not running. Whenever the alarm is triggered, it stays on until ignition is cycled off/on, from what I can see, irrespective of what happens to the resistance after triggering.

 

Weird observations on the way to the above:

1. When trying to directly measure the resistance between the probes in the coolant, with a reasonable quality (£30-ish?) multimeter, I was seeing 18 Megohms (20M highest range). Guess some sort of electrolysis mechanism must be enhancing the conductivity during whatever the car does to sample it, but the meter doesn't test with enough energy to make this happen???

2. When substituting a pot for the tank, I couldn't seem to measure any sort of voltage, dc or ac across the pot, even while the alarm was being triggered.  Maybe something 'pulsey' and brief going on that the meter wasn't picking up? Or something occasional that my concentration wasn't sufficient to spot? Was using a different, much cheaper meter the other day (post #12) when I was seeing 0.3V dc with just meter plugged into socket, no pot. Confused.

 

Today we de-pinned the socket on the owner's car to check for corrosion where the copper wires were crimped into the connector pins/skts - absolutely pristine, shiny fresh metal. 

 

He's no longer bothered, 'cos it reliably gets reset by cycling the ignition - which he does on the move - but I still have a need to understand how it works.

 

I'll keep trying, but if anyone knows anything that could help, please speak up!

 

Ta.

Since the coolant light also serves as a high coolant temp warning, could it be possible that there's some fault on that side of things? Maybe wiring or possibly the new sensor is faulty? I know a faulty new sensor is unlikely but these things do happen sometimes.

Cheers Lee, I'll add that into my investigations.

A friend of mine had a few years ago a 6n Polo with an oil pressure warning light on. He had to replace the instruments panel in order to get rid of it. It was a PITA to identify the issue.

Just the other day some kind person popped up a post saying that they'd solved this problem (or similar) by just pulling the two plugs off the back of the clocks and then re-connecting (i.e. bad contact problem)..http://www.briskoda.net/forums/topic/372997-coolant-level-warning-light/#entry4391443

If I can persuade the owner that this is worth a try, we may see if that works for him.

This is might be a good point. In cold mornings, I find my instruments panel glass covered with moisture. I don't think I want to know how it looks inside. 

Edited 28 September, 201510 yr by Alexandru

Sorry if this seems lazy (it is  ), but is there a how-to on here anywhere for getting the instrument cluster out of a Fabia? I seem to remember reading that it isn't particularly difficult?

 

Edit: This thread seems to cover it.

Getting the cluster out is a doddle. Once the screws are out I used a stiff piece of wire (like coat hanger wire)  bent into a small hook (L-shape) to push behind the top of the cluster and then pull the top forward.

I've had my first coolant alarm this night. I was driving around the city and out of nowhere it started beeping twice and with that red intermitent light flashing. The engine temp needle was at 90 degrees so I knew it must have been the expansion tank connectors. I've pulled over, reseated it, but thr alarm came on again after less than 1 minute after I started the engine, maybe less. Since it was 1am, I've decided to keep on driving, with the cabin heater at 3rd and on max warm. Had to stop to drop my future wife, couldn't resist so I checked again the oil and water levels, reseated the connector and for 5miles the alert didn't came back. Pulled out my laptop, scanned it, it was pretty clear, which was and still is darn akward since I am used for the past 2 years to get o2 sensors errors and fuel trim stuff. Tried to the engine over 3000, allowed it to idle for ~5 min, it was as good as new. I tried to reproduce the alert and I've unplugged the connector from the expansion tank, the alert came back after less than 1min after I started the engine. So IMHO, that was the one causing the mess. Tomorrow morning I will check the connector, maybe clean it, but the tank is kind of new, I've replaced the old one less than 6 months ago. I am now intrigued why that o2 errors are no longer logged. The fact is, last 5-6 times, I've reffiled from different gas station companies that I have been used to.

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I bought a cheapo secondhand spare cluster on ebay the other night, compatible with her 1.2, so I'll be tearing that down when it arrives to have a look at the circuit board and whether there are any visible issues with the solder joints for the connectors.  I'll get some photos, especially if there's anything interesting/useful to be seen.