Help, Octavia MK3 overheating during regeneration ONLY when car is not in motion, IE standstill at lights, in traffic etc, but ok if car is in motion. Had timing belt, water pump and radiator done, had pre and post dpf sensors done 6 months ago, any ideas please? Thanks

Did you have this problem before the water pump and radiator were done? Or when this problem started?

 

Why was radiator done?

 

How about the notorious silica bag? Do you have it? ('mit silikat' written on the coolant expansion tank, google / search forum if necessary).

Is the radiator fan running during the regen?

Had the problem before water pump etc, was hoping someone on here might have come across something similar, maybe the egr is stuck or egr cooler is leaking, the fan does run when you switch engine off mid regen

The radiator blew after having the water pump done, like it's too pressurised, it won't overheat whilst the car is in motion during regeneration only when static

1 hour ago, txdriv said:

Had the problem before water pump etc, was hoping someone on here might have come across something similar, maybe the egr is stuck or egr cooler is leaking, the fan does run when you switch engine off mid regen

But does the cooling fan run DURING the regen while the engine is indicating overtemperature?

Edited 25 November, 20241 yr by Warrior193
emphasis

I'll check next time it happens, thanks

No the fan isn't kicking in

If that is while the temperature gauge is indicating high temperature, it will be the cause of overheating while stationary, particularly while undergoing a DPF regen. You previously said that the fan does run when you switch off engine during regen, so I'd suggest checking the coolant fan thermo-switch. 

Thanks

On 25/11/2024 at 13:30, txdriv said:

The radiator blew after having the water pump done, like it's too pressurised, it won't overheat whilst the car is in motion during regeneration only when static

oh heck - I hope you haven't suffered from the "Bag of Death" inside the header tank - i.e. its split and got into the cooling system.  If so, you need to pressurise flush your cooling system until all the silicon has been flushed out, then refill with G12Evo.

Heater matrix or egr cooler 

The heating is hot, silica bags not split, doesn't overheat at any other time except whilst regeneration only if the car is static, when the car is in motion it doesn't overheat. Could the egr be stuck open or shut, or the egr cooler not getting any water in, or the secondary water pump not working maybe

Edited 26 November, 20241 yr by txdriv

Check reason for coolant fan not running when engine overheating.

If 'Mit Silicat' bag is still in expansion tank, remove it or replace EV for one without it ASAP.

The EGR should be inhibited during regeneration because it reduces the combustion temperature so whether coolant passes through the cooler or if the EGR valve is stuck open is of no consequence to overheating.

 

Mmmmmm.................. Actually under that situation (valve blocked open) the engone coolant will have more heat to deal with but the cooling system has more than enough capacity, the fan not running should be investigated, I know it comes on after switch off but should it at idle with the vehicle stationary during regeneration?

 

 

The cooling fan should definitely run if coolant temperature has risen above normal, particularly when vehicle is stationary. Coolant fan not normally required at normal engine load and with vehicle moving at speed. 

Given the untruths the VAG temperature gauges display its possible that the temperature guage might rise visibly before the cooling fan cuts in.

 

I dont know because in the 26 years I have been driving VAG diesels the cooling fan has never once cut in to reduce the coolant temperature, only for the air conditioning.

 

That is probably more of a reflection that I have never been in a traffic jam since moving to France!!!!!

 

Only a slight untruth, one time leaving the parking field for the Paris air show it was 20 minutes of crawling and one time an autoroute was closed due to an accident and again we crawled for 15 minutes to the exit, never ever come to a complete standstill for any length of time.