So I'm losing coolantz struggling to locate where. Still investigating, I can't see anything suspicious in the coolant bottle.
Ideally I'm gonna need to get underneath and inspect all the hoses - the car is 25 and used daily, I don't really know if any of the coolant hoses have been replaced.
My worry is that the head gasket is dicky. It overheated last year (blew a hose off and emptied it's coolant all over the A14).
I'm a bit worried the head may be a little warped but can't tell.
Any advice on tracing where this coolant could be vanishing? It's not blasting out anywhere, I'm just topping up every few drives. Occasionally I'll have no heat from the fans, check and top up.
I'm assuming the 1ZZ is cheaper to replace than get the head gasket swapped out?
Is there not some sort of glow in the dark coolant leak detection fluid you can add to help trace.
Before you investigate the head gasket, take out the plastic frunk surround and the frunk itself, then you can see much of the hoses and cooling system plus the radiator (which is your most likely culprit). Check the water pump for drips.
Do you park on the street or on a driveway? If on a driveway, check for drips under the car after it has been parked overnight.
Head gasket failure is rare on the 1ZZ. But a major overheating incident could cause it.
I'd pull the spark plugs and look for any crusty build-up on an electrode, which would indicate coolant in the combustion chamber.
If you can get hold of a boroscope for your phone, take a peek in each of the cylinders (you will need to roll the car in a high gear to get the pistons down in turn), after the car has sat for a while, and see of you can see the shiny reflectance of any liquid sitting on top of a piston.
You could also run a compression test to see if any cyinders are weak.. You should see around 185 psi, but mainly you are looking for one cylinder being low compared to the rest.
If it is a head gasket, it's easier to do the job with the engine out. I've done one with the engine in and I wouldn't try it again - it's a PITA.
Good advice here, thanks folks. I'll do some digging.
First place to check would be the bottom entry to the radiator. IIRC it's on the passenger side. The radiators all seem to go here eventually.
Pressure test the cooling system for leaks.
Norman
Small update - Ive not been able to find a leak from the radiator, but I'm not ruling it out, since with how bad the weather has been lately I've only been confident that the plastics were dry enough for me to be sure it wasn't leaking on one occasion (car is stored outside on the drive, but it has rained almost every day here for weeks).
Spark plugs seemed ok to my eyes, nothing scary on them, just a little carbon-y. Gaps were ok, threads were pretty clean and the ceramic insulators were still creamy white.
Ardent's suggestion of a luminescent fluid is a good shout, I have some oil-based fluoro dye which I can try, haven't got round to that yet (again, weather).
I couldn't see anything particularly obvious from the water pump either, but again the car is used every day and has had a good soaking from the rain. That said, there was no water dripping under the car overnight - oil however, there is.
I haven't managed to do pressure test yet, as I don't have the gear.
However, somewhat mooting it all - I had some savage belt squeal on Saturday while driving home at about 60mph, very sudden, and then the accessory belt decided to strip itself and flung a whole rib off.
Its still intact (minus about a third of it) on the pulleys but I don't dare drive it yet.
I don't like playing parts roulette, but with the age of the engine now (approaching 93,000) and the mystery coolant loss I still haven't tracked down, I'm going for the nuclear option and replacing the lot: water pump, tensioner and pulley, thermostat, radiator and belt - I figure if a pulley is dead/dying, the amount of work getting in there justifies getting it all sorted at once. I love this car and I miss driving it (I'm currently borrowing a Corsa...) so hopefully I can kill 5 birds with one stone here.
Ive managed to source all the bits, which wasn't terribly expensive either I was pleased to find. Some of the work I can even do myself.
Thank you all for your help and advice so far - I know this doesn't really help to narrow down the problem much, since the culprit will be lost in the replacement bits, but I will report back once it's all done with.
False economy not to.