Warrior193

Presumably your Octavia does not have automatic Stop/start?

What @dsgman is attempting to warn you of is that the 1.5 ACT engine requires specialist (and expensive) locking equipment to maintain correct valve timing. There are many references in this forum where the cambelt change on 1.5ACTs has been done incorrectly.

Way, way too low with just ignition on - 8 volts is even too low while the engine is being cranked! Also check for loose terminal connections while testing the battery.

The second variant has to be for some extra ancillary, probably via a flat belt - suggest just getting the one that matches original.

Clearly, 225 deg.C isn't possible without the coolant system venting - so there is at least a sensor issue to address.

Correct, adding glycol to water actually lowers the specific heat capacity of the coolant.

Hello, welcome to the forum. Try contacting one of the specialist performance car builders - they'll have a pretty good idea of what will fit - or be made to fit.

Hello, welcome to the forum. I'd take a guess that the spring assisters would be aftermarket too - I believe that any changes from the factory for towing pack would involve fitting heavier-rate springs and shock absorbers.

NO, definitely not! - DOT5 is not compatible with most / all ABS systems. DOT5.1 MAY be suitable though

The 12 volt sockets are permanently live on the Mk3.

^^^This, something has clearly changed (gone wrong) with this engine, as the issue is relatively recent. The 'vibration' is being highlighted when the engine switches to 2-cylinder mode - NOT caused by it.

Pretty sure that the fluid is not tested for MOT, and the brake efficiency test that is actually part of the MOT would almost certainly NOT show up high moisture content in the braking system - that WILL show up in braking while descending a long slope - or a hard stop from high speed!

DTC 171900 could very well be a result of your momentary losses of power - that can be a flag that your ECU is limiting engine power to prevent damage to it. The cause of that should be investigated.

Brake fluid change isn't the same as the usual 'Cash Cow' scams - possibly not actually required as frequently as stated, but the fluid should at least be tested for water content on a regular basis and changed when required. I don't see members deriding regular oil changes as being an unnecessary cash grab. The brakes are your primary safety system - and terminal brake-fade is something you really do not want to experience!

What did the old plugs look like - especially the non-ACT cylinders? If nothing unusual was noted with plug electrode colour, I'd suggest a compression test.

Clearly something has changed then - it's not ACT triggering that is your problem, but something affecting the operational cylinders. Has a scan for misfiring been done? Have the sparkplugs and coil packs been checked?

Hello, welcome to the forum. Does the ADAS warning flash up when this event occurs?

Hello, welcome to the forum. I'd take a guess that there may still be part of the broken, old cap in the filler - can you post a photo of the filler opening? There is a possibility that the plate you refer to in the filler is a baffle-plate. Provided the filler opening is completely clear of all debris from the old cap, everything should be OK so long as the replacement does actually seal correctly and lock into position.

Has it always vibrated severely when it switches to 2-cylinder mode - or this more recent? I can't see ACT mode alone causing severe vibration, as it is only supposed to operate when the engine is lightly-loaded. Have you had it scanned for misfires in either of the two non-ACT cylinders?

But OP says Kodiaq in the text in first post.

'Warming up' the engine while idling is a potentially damaging action - the usual recommendation is to move off as soon as practical after the engine is started, and drive gently until engine has warmed up. If you engage Sport mode, the IC engine will share the load with the EV while warming up - another option would be to fit an auxiliary engine block heater.

From a little research - if your vehicle is a Kodiaq PHEV, there is apparently no ICE mode available - however, if you select Sport mode, the ICE will run alongside the EV. The IC engine should also run if you don't recharge the battery via the socket - although that rather defeats the object and will increase fuel consumption.

Hello, welcome to the forum. Do I assume correctly that you have a PHEV? Are you saying that you are unable to get the ICE to run, and it's running only in EV mode?

Hello, welcome to the forum. The contents of the bag (or capsule) if fitted are Silicate, and this was fitted to the coolant expansion tank for extended coolant life and corrosion protection for the engine. The problem comes from the bag splitting and releasing silicate granules into the cooling system, blocking small channels - especially in the heater matrix. AFAIK, the problem only appears with the bag (if fitted) - later vehicles had a plastic capsule insert fitted instead of the bag. Even later vehicles dispensed with the silicate insert - I believe this may have been when coolant was changed to G12evo.

Given the highly hygroscopic nature of DOT4, I doubt there is such a product as 'long-life' brake fluid.