Oil in reservoir tank

Hello,

The brown oily film could just be filmy gunk that sometimes collects in your cooling system. It could be coming off and breaking up from the flush and fills. Check your vehicle's engine oil. If it looks like coffee with creamer in it, then your new head gasket has failed. here are a couple of tests you can do to ensure the integrity of your vehicle's head gasket. Here are the links below:

https://www.2carpros.com/articles/how-to-test-engine-compression
https://www.2carpros.com/articles/head-gasket-blown-test

Please go through these guides and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros

Hello and welcome to 2CarPros. Just to jump in, if you have no overheating concerns then I would suspect the oil cooler has failed. The cooler is located just above the oil pan on the block. If it has an internal leak and coolant and oil has mixed then I recommend you replace the cooler. Flush out the cooling system with water and replace all rubber hoses. Example both upper and lower radiator hoses, heater hoses, and oil cooler hoses.

I have seen mechanics replace the head gasket for this concern only to end up been the oil cooler leak. It is not a common fault but it does happen. I would start with that. And the reason you need to replace all rubber hoses is because oil does some serious damage to the hoses where you will have more headaches. Hope the information is useful and keep us posted please.