I was checking the level of oil in my car and I've found some yellow foam in the oil cap, the car has 120000 Kilometers and 12 years; the head gasket is the original, what could it be? Do i need to replace the head gasket?
What does the oil itself look like? If the oil looks like oil (and not milkshake), just clean the cap and call it a day. More than likely you just haven't been running your vehicle enough. You need to take it out and completely get it warm which will burn off any moisture which might get into the crankcase. Moisture is a byproduct of the combustion process and will get into the crankcase. If you don't get the oil hot enough through usage, the yellowish foam can collect in the oil cap.
Concur - I had similar, a small amount of yellow foam like this turned out to be condensation and was resolved by running the engine for a while without the oil filler lid. This let the vapours escape. criggie.org.nz/pictures/landrover/2007-06-10_head_gasket/…– CriggieMay 7, 2022 at 0:46
1@Criggie - If you get your engine hot, the PCV will take care of the vapors.– Pᴀᴜʟsᴛᴇʀ2 ♦May 7, 2022 at 1:14
...if the PCV system is working - mine was not at the time.– CriggieMay 7, 2022 at 5:23