Thanks Ian, I've never had a problem with the temp gauge fluctuating, is that what your saying you had? I just have the dropping coolant level under load which could be lots of trapped air, and good advice on how remove it.
On another note my silicone job has failed today decided to bite the bullet and buy a new expansion tank.
Screw is defo knackered but not sure yet if it's going to fix my underlying problem.

the bleed screw is a poor design , an easy fix is to drill it out and tap it with a 12mm tap

jobs a good un

Yes I had so much air in the system, the temperature fluctuated. I am not saying you need to have the same symptoms, but in my experience, dropping coolant level when revving the engine is a sign of air. Do you have a FBH? In that case this should probably be run also (it has its own circulation pump). I did run mine to flush out air.

Thanks for the advice Ian, I'm glad it's likely just air...
I silicone'd the crap out of the plug last night and it's held today ok.
Going to buy the new tank anyway and fit over the weekend, I'll try what you have suggested to get the air out and hopfully that will solve my problem, fingers crossed.

Oh! and I don't have a FBH.

dingg1 wrote:

the bleed screw is a poor design , an easy fix is to drill it out and tap it with a 12mm tap

jobs a good un

Update.
Replaced the tank and took Ian's advice to bleed (screw off for > 20 mins plus revving every so often)
Still seems to be surging... However I did for a sporty drive and didn't get an error.
Run it for a while longer and see what happens.

Update on this.
After replacing the expansion tank I haven't had any problems.
I did check when I first replaced it and went through what was suggested by Ian and it was still surging however I have been running for a good few weeks now with no issues.

Update on this... (probably related)
Driving to Ikea last weekend for some furniture shopping and meatballs when the RR decided to boil the coolant!
Temp gauge at 3/4, steaming coming out the expansion tank and boiling hot.
I was luckily able to pull over and let it cool down for a bit. I was on the by-pass so had to drive to the nearest stopping place which was a car wash. Let it cool and slowly filled up with water and drove to Ikea (only 1 mile away). When I got there steam and water was boiling like hell in the expansion tank and going everywhere.
Needless to say I got recovery to take me home and handed the car back to the garage I bought it from.

Before I did I had a look and with the engine idling I couldn't see any flow coming into the tank through the top hose under the bleed screw? Also the rad pipes were cold.
I assumed then there was no flow (water pump maybe?) but the water pump was replaced along with the thermostat recently.

Garage has had a look and reckon there is flow and the issue is the expansion tank cap...?

I have heard of these turning into 1-way valves (letting air in but not out) is that likely my problem? Also might explain the surging from before.

Seems too good to be true?

99% sure mine has had a water pump, but drove to Czech Republic and kept getting low coolant warning message on dash.

Topped it up and checked every time it came on and the radiator was leaking on the right hand side which is fairly common on these, so worth checking this.

cheers Alex

2018 Skoda Kodiaq vRS
2009 Caterham Supersport Race car
2007 M5 Touring
2005 Range Rover Vogue SE Supercharged
2004 SL55 AMG