Hello

I have a Octavia Scout 2litre diesel 17 plate

For 52 thousand its been total reliable, but on Christmas day it said it was overheating but opening the bonnet, no signs

Full details

Set off in lightly loaded car to drive to Oxford from Brum

10miles to M42, turn towards M42 and shortly dash lights up and tells me its overheating. Temp gauge is a 120 but oil at 105

Slow down to 50 to crawl to safe place. Temp gauge quickly gets back to 90 as it has always been

Speed up a bit but gauge goes to 120 again. Pull over in HGV type layby.

Open bonnet, no water splashed nor the sort of smell you get with a hot engine. Wait 10 minutes, touch plastic reservoir. Its hot but not untouchably hot.

Highway officer pulls up and suggests I drive to next junction.

I set off but the needle stays at 90 on the water and 105 on oil

Decide to carry on keeping eye on temps.

I switch heater on full

Make it to north Oxford absolutely fine.

I had it trailered back as I didn't want to be waiting beside freezing motorway at 23:00 on Christmas day

Past few days I've been driving it around and temps of oil and water exactly where they should be and rick solid

Is this a known issue? Sounds like a sender switch to me. Ideas please

Thanks for any help

It could be, but looks like you need a mechanic to diagnose. Water Pump. Possibly. Is it a manual gearbox?

For the minimal cost, probably worth changing the primary coolant NTC sender first. There maybe a secondary but that will not usually control the display gauge.

Have you had a read of the water pump thread?:

Gaz

Is your coolant level ok. It may be a faiing waterpump or perhaps an airlock thats cleared itself or as simple as a sticking thermostat. I agree with changing sensor anyway and would monitor it and keep an eye on coolant.

Alasdair

Thanks for all the replies

My initial thoughts are sensor

I have been driving it on short distances today and the temp is solid at 90 and oil at 105

I plan to do more miles to see if it comes back

Will read about the pump

Thanks again

OK, just read most of the pump thread - that sounds like my issue 100%

Once my Skoda dealership has diag'd it I'll submit my details and remedies

Thanks

common for the heater matrix to block up on these aswell

On 29/12/2025 at 18:31, Gaz said:

Have you had a read of the water pump thread?:

Gaz

I've added my details to that thread, Gaz

A few observations

Since Christmas day the temp has got to 120 degrees there times but by driving at a constant 50mph the temp falls back to 90 in jerks. Only once after it has fallen back has it risen again.

In between those 3 events the car has stayed at 90 for water and 105 for oil for 100s of miles

The Skoda mechanic who changed it implied the bypass sleeve went from solid stuck to like mine sticking occasionally

Giving the car a good run tomorrow, will be back if it doesn't work

The car is fine now, but an observation

The rate at which the water gauge got to 90 is much slower now I have a new water pump/shut off valve.

Maybe if you see the needle getting up to temp much faster than was normal this is a leading indicator that something is wrong

When was the last time a coolant change was done on the car? Coolant may have got too weak to help cool the car.

The pump change has fixed it thanks

On 23/01/2026 at 02:09, varaderoguy said:

Coolant may have got too weak to help cool the car.

I dont think the concentration of coolant helps cooling at all.

Water is the best cooling medium due to its enormous specific heat capacity, but we mix it with glycol etc to prevent freezing and corrosion of cooling system. The mix also inhibits boiling to some degree but that is largely due to a pressurised cooling system.

Really diluted coolant probably cools the best

9 hours ago, BlueWagon said:

I dont think the concentration of coolant helps cooling at all.

Water is the best cooling medium due to its enormous specific heat capacity, but we mix it with glycol etc to prevent freezing and corrosion of cooling system. The mix also inhibits boiling to some degree but that is largely due to a pressurised cooling system.

Really diluted coolant probably cools the best

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

Edited 24 January24 Jan by Warrior193
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