Basically the title. Had my timing belt / water pump changed on my 1.6tdi Octavia (used OEM parts) done by a mechanic.

Everything was fine for a week - drove car maybe 200 miles over 5/6 journeys and no issues. So, I then go on a long road trip... About 3 hours in to a 6 hour motorway journey I see coolant temp rising... This has NEVER happened before. Also, oil temp went up to 110. Coolant go to 115 before I fully noticed and I immediately switched off cruise control, slowed down and within 10 seconds coolant temp was back at 90... Weird...

So, I carried on driving... Car felt fine - I switched heater on max into the car to try to dump any extra heat. All was fine for 5 minutes or so. Then, on a big uphill again coolant temp rises... Goes to about 100 before I completely stop accelerating and go down to 45mph or so and it immediately drops back to 90 degrees.

I pull over, give the car 10/15 minutes to rest as I'd been driving 3 hours anyways. Hoped it would somehow fix itself. Carry on driving... Same thing happens again on a big hill... Weird. This happens 4/5 times but fans were blowing hot the whole time and the coolant / oil never got concerningly high. But I was having to completely stop accelerating anytime the coolant temp rose, and it immediately would stop rising.

Then, randomly after maybe 45 minutes of this, it completely stops. I went up huge hills and oil temp and coolant temp stayed stable. Hooray, I thought. It was gone. It stayed like this for 2 hours or so...

But, then again, randomly coolant and oil temps rise again to 100 or so degrees. I again have to let off cruise control. This happens again 4/5 times... But, eventually I made it, without any permanent damage but I am now stuck asking the question - what could this be? Coolant temperature returns back to 90 (from 100 or so) in 5/10 seconds after completely letting off accelerator.

I am now 400 miles from the mechanic who fitted the waterpump (who would likely look at it / fix it for free given the circumstances). I'm reluctant to go to a garage as if it is an issue with the waterpump I will have to spend £700-1k on repairs...

Does anyone know what I should be doing here? Symptoms seem like a possible airlock to me but hasn't cleared even after cooling overnight and driving again? What should I do? I'm currently street parked in a busy city so can't do a whole lot of DIY work.

TLDR; Random overheating 500 miles of driving after water pump replacing. Then stopped for 100 miles. Then restarted. What could it be?

air in system or variable water pump not working as it should..

also thermostat can make problems.

Edited 28 April, 20251 yr by imart143

Has the coolant level in the expansion tank dropped since the water pump was fitted? If so it could indicate that the system is still burping itself of trapped air. There is a procedure to follow using VCDS or similar to ensure no airlocks when refilling the system after draining. It opens & closes different valves at different times AFAIK.

When my 1.6tdi has it's first pump change the indy garage didn't complete this task fully and I had to keep topping up the coolant for a couple of weeks (~1000 miles ) before it settled down. I didn't get any overheating warning signs though, just low coolant light on the dash.

If the belt has just been done it could be the timing is slightly out? You said it tends to overheat when uphill/under load. Does the car sound and drive ok and has the MPG changed.

Alasdair

Have you had a look at the water pump thread?:

And does the car display any of the symptoms therein?

Gaz