[jack_chapman]

I was topping up my collant on my Peugeot 307 and I found some white gunk on the lid of the expansion bottle, any ideas what it could mean at all?

 

[508GT180]

It used to be that gunge round the oil filler meant coolant in the system and a probable new cylinder head gasket. Whether that applies the other way round ie oil in the coolant I don't know. I'm not a mechanic so best wait for someone else

PS Welcome to the forum.

 

[reliable406]

Depends on engine can be a sign of head gasket failure but only on petrol engines

Can be a sign of oil cooler failure on diesels

Can also be a sign of some numpty putting oil in there by mistake !!

 

[F13Dev]

In general gunk that looks like mayonnaise in the coolant or oil would likely be the result of mixing oil and coolant under temperature. Often the result of a head gasket failure, but can be other things.

I'd check the appearance of the oil, both via the dip stick and by looking under the filler cap.

Could it possibly be caused by mixing red and blue coolant? The different types don't mix well and can cause havoc.

 

[jimmymarsbar]

The colour of the coolant shouldn't affect it - it's just a dye that's used to identify the liquid as coolant, and to give an indication of over-dilution. Colour doesn't specify type of coolant.

You should only be using OAT coolant, and when topping up, aim to keep the concentration the same as the older coolant (ie. try not to put 50/50 in if the older mix was 70/30). Always read the label

It would help if the OP posted the engine info?