Gunk in the coolant tank

[mossie54]

Gents - RS133 2010 reg. I am looking for some guidance as to whether this is a problem I need worry about, or get sorted before the extended warranty runs out. Car has 17,000 miles on the clock. I have "emulsion" in the coolant expansion tank. Normally if this was in the oil filler cap I'd say it was water in the oil, but it isn't. Car runs fine and doesn't overheat.

Thought about taking the tank out and cleaning it out to see if the gunk comes back, but don't fancy taking the whole front apart to get to it.

Suggestions please.

 

[oscar]

start by draining the coolant out. remove the radiator and check to see if this same 'gunk' is in the radiator.

what colour is the gunk? is it the same mayonnaise type emulsion that you see around the oil filler neck / cap after a short drive? if so, you have a grave problem. either a cracked engine block / cylinder head, or a head gasket failure allowing oil to enter the water jacket. if the later is the case, get it to renault immediately because this is going to be a major engine strip down job. it will entail the following

new water pump
removal of the cylinder head with headgasket replacement
cooling system pressurised flush
new radiator
cambelt / timing belt replacement

if left to chance, and you need to repair yourself out of your own pocket after warranty has expired expect to pay 1k+ before VAT...minimum for the head gasket fix if the job is done correctly.

if the engine block or cylinder head has cracked, then expect a 2-3 grand bill. so better to let renault foot the costs right now!

 

[mossie54]

Thanks for the worrying reply Oscar. If the problem was that serious wouldn't I be seeing emulsion in the oil cap too? Yes it is a cream colour.

 

[oscar]

no, the oil pressure is much greater than the cooling system pressure. oil pressure is around 20psi at idle and 45psi at full throttle wheras the cooling system will vary between 0,8 bar and 1,35 bar (20psi the latter) so the oil will only make it's way into the coolant as the higher pressure will always seek the low pressure exit if you understand what i mean

unfortunately, this does indicate a head gasket failure. however, you can purchase something called a 'block tester'. it's a container filled with a special fluid, you suck in some coolant into it and if it has any combustion gasses (which will be contained in the oil) then it will turn a different colour. the fluid is blue, if it turns yellow then you're head gasket is shot. they cost around 25-40 pounds usually, and are readily available from e-bay