Vauxhall Astra Hatchback 1.6 8v 2004 - New car troubles - Aidan Hickman
I just bought a new car (well new to me) and it has a few issues.

Basically it reports the wrong temp, the cars running fine and I just fitted a new thermostat like a hour ago and it still runs reports cold however the heating is boiling, the engine has a tapping noise however I have been told it’s just noisy tappets and not to worry unless it’s actually affecting the car, I found mayo on the oil cap so I replaced the thermostat as many people say to do, the engine management light flashes when pushing the engine however the car isn’t running slow or even rough if anything the cars very nippy, no white smoke or power loss however the engine can run rough after giving it a bit of stress and it’s got bubbles going into the water tank however I’m quite sure it’s not losing any coolant and there’s no oil in the coolant.

EDIT: I forgot to mention the car is my daily driver and it works well, apart from the issues mentioned above planning on keeping it for a few years if I get these issues straightened out.

It’s my first car and I am in love with it so losing it would be a real shame.

Thanks for any help.

Edited by Aidan Hickman on 17/01/2019 at 12:03

Vauxhall Astra Hatchback 1.6 8v 2004 - New car troubles - hardway

Possibly a suspect coolant temperature sensor.

Vauxhall Astra Hatchback 1.6 8v 2004 - New car troubles - Aidan Hickman
I have read about that and bought one just in case as they’re really cheap, I’ll replace it later and let you know

Appreciate the help
Vauxhall Astra Hatchback 1.6 8v 2004 - New car troubles - Aidan Hickman
Fitted new CTS but no change on idle taking for a decent drive later see if there’s any difference and I’ll let you know.
Vauxhall Astra Hatchback 1.6 8v 2004 - New car troubles - Aidan Hickman

After a drive with the new CTS the temp sits between the two white lines in the cold area not holding heat

Vauxhall Astra Hatchback 1.6 8v 2004 - New car troubles - elekie&a/c doctor
The accuracy of the cts is dependant on it actually sitting in the flow of hot coolant. I would remove the sensor and let the engine idle for a few seconds to see if there is any coolant flow.. Do you have access to any diagnostic kit ? You would then be able to monitor real time engine temp.
Vauxhall Astra Hatchback 1.6 8v 2004 - New car troubles - John F
..... I found mayo on the oil cap .......and it’s got bubbles going into the water tank.....

Not what you want to hear but I suspect the previous owner, after possibly unsympathetically thrashing/neglecting the old engine (how many miles?), has noticed these early signs of CHG failure, and offloaded it pronto before it becomes obvious.

Vauxhall Astra Hatchback 1.6 8v 2004 - New car troubles - andrew bairsto

First signs of a cylinder head gasket going .