rodel@1629

Hi Friends, I have a 2017 GLS 450 having coolant issue. Coolant seems to expand out of the reservoir cap when driving long distance. Seems to eveporate since i dont see any leak anywhere else. I only see dried up coolant around the reservoir area. When it cools down, the coolant level goes to 1/4. When i open the cap, it release presure and level goes to 3/4. No visible leake on the other hose. Engjne is not overheating.
Took it to dealership and they said nothing is wrong. Took it to local mercedes mechanic and replaced the lower readiator hose. That did not fix the problem. Replaced the thermostat, return line, reservoir and cap. That also did not help. Purchased the block tester kit. The test was possitive. Blue fluid turned yellow.
Questions:
1. how reliable is the block tester kit?
2. I called another mechanic and scheduled a diagnostics. Over the phone, he is suspecting its the turbo causing the issue. Does that sound right?
3. From my research, it can be the head gasket, the car runs fine and dont see white smoke.

Please help. thanks in advance.

jkaetz

You should ask the W/X166 Folks for a 2017. That said, it needs to be properly diagnosed:

• Is the system being pressurized by something? (Head gasket)
• Are there combustion gasses present in the coolant? (Head Gasket)
• Is the radiator cap holding the pressure it's supposed to? (Bad cap)
• Coolant getting hotter than it should?

Some of these can be checked with the proper tools if you're mechanically inclined but I see little reason to speculate as there are many possibilities.