ML-430 Frothy Oil Mixture

[EPineda]

I have a 99 ML-430 with 103,000 miles on it. It's being maintained quite well and had no problem the last 2 years. Synthetic oil (Mobil #1, 0W-40) was always used and replaced with a new fleece filter every 3500-4000 miles.

Lately, I had a tell-tale sign of frothy oil under my oil cap that started to show a few weeks back. This past weekend while checking the oil, it seems there is more frothy oil mixture now than before. I stopped using the car all together to make sure I don't damage the engine until the problem is solved. Although the engine temperature was (I thought) higher than normal (3/4 on the gauge which I think was normal), the engine never overheated.

Are there simple test to determine if I have a 1) blown head gasket, 2) bad EGR, 3) thermostat problem 4) or any kind of problem that can cause this?

I would appreciate any suggestions or tests to determine the cause before I go into an expensive trip to a dealer/independent mechanic.

I appreciate our expert's help on this problem.

Thanks an awful lot!