Gloop in the radiator expansion tank

[ralabaf]

My radiator low-water warning light flickered today and when I took the top off the expansion tank I saw some pretty yucky gloop in the water. It's sort of brownish thin blamanche. There's a lot of it.

No sign of anything when I took off the engne oil filler cap.

Is this oil in the coolant? If so, I'm I likely to get another ridiculaously large bill for my old J-reg 3-litre Mercedes?

[vikingaero]

Sounds like the head gasket has gone and oil is mixing with the coolant giving rise to the rust colour gloop.

[The_Economist]

Could be head gasket. How long ago did you do a oil change. If the oil out of the sump or oil filter is of the same consitancy as the expansion tank and the car is running hot then all most certainly is head gasget.

[epninety]

It certainly sounds like oil in the water, usually described as 'mayonnaise'. You won't always have any visible effects in the sump oil, depending on the exact fault.

It's most often a head gasket, but there are other (some easier to fix!) faults that can cause the same problems. A bad inlet manifold gasket will do it on some engines, as will a cracked or 'pin-holed' oil/water heat exchanger.

I'd find someone who knows the engine well to see if there are any common problems before whipping the head off.

[iluvmylexus]

had a merc 190 e last year with the same symptoms,
it was a head gasket, ran it locally for several months before the engine finally went kaput.
almost certainly a head gasket in your case

[plane_boy2000]

Sounds like head gasket. Have a look in the oil filler cap to see if there is any more gunk in there.

[iluvmylexus]

Sounds like head gasket. Have a look in the oil filler cap to see if there is any more gunk in there.
they dont always blow water into the oil so you dont always get mayonnaise on the filler cap, all the mercs i have seen tend to blow oil into the cooling system so the mayonnaise is in the header tank.
it is a good idea to check though
and keep a sharp eye on the temperature needle

[ralabaf]

Thanks everyone.

It was the lack of any sign of contamination when I lifted the oil filler cap that made me wonder.

Effing typical, this year alone I've had to replace the distributor cap, rotor arm and MAS box. That on top of an exhaust last December. I'm spending more than the car is probably worth. Time it was traded in I guess.

[vikingaero]

It was the lack of any sign of contamination when I lifted the oil filler cap that made me wonder.

My dads A Class Merc has mayo on the filler cap and tube. The coolant is fine and the Merc garage says that on the A class the filler tube is really tall and you get a lot of condensation which gives rise the the mayo. Plus he does loads of short trips which doesn't help.