So, my gl63 has had a coolant and oil leak for the past couple of months. They were both small leaks but they needed to be addressed. I have been waiting for free time to replace the radiator and track down the oil leak. Using an endoscope, I had an idea of where it was coming from. The coolant leak was at the strangest spot. I kept getting a very small amount of coolant on the driver's side top radiator mount that connects to the top support as seen in the picture. I went to tearing just about everything apart on the front side of the engine including the radiator. I never did find the leak in the radiator but I'm sure it was just a very small crack or pinhole due to stress on the upper support.

As far as the oil leak, it was coming from where I had suspected which was the oil thermostat. It


was from an O ring under the cap that is pictured. The good thing is that I had an extra oil ring that I had laying around. It happens that one of the O rings from my x164 gl450 oil filter kit fits exactly on the oil thermostat cap. It sealed great and I have no more leaks from it. I also removed the oil filter housing just to change housing gaskets as it is not easy to get to these items and I figured that I may as well change everything that might fail in the future.

I do want to add that since I now have 140K miles on my GL63, I decided to change the coolant thermostat, idler pulleys, belt tensioner, serpentine belt, oil filter housing seal, and driver's side turbo coolant lines.

When I went to check the turbo coolant lines by grabbing them and lightly pulling, they both snapped off with just the slightest pressure. I would say it would have been a matter of months until they failed and luckily, it didn't happen on one of my road trips. I had changed the passenger side turbo coolant line a few months back because it had been leaking.

In all, I spent almost $1500.00 on genuine Benz parts and it took me about a day and a half. I think it was time and money well spent to keep this thing going. If you have a high mileage x166, I would seriously think about getting those driver's side coolant hoses changed.

 

Weirdly mine has just started showing similar coolant around that mount, I cleaned it off and it’s very slowly coming back. 2014 69k GL63. What was causing the coolant leak in the end?

I’m still under MB warranty (am in the UK so is Allianz) so will be booking it in, but will take a look before when I get a chance.

 

I found a post where someone had repaired it but cleaning and dried the area thoroughly and putting jb weld in there. It appears that it leaks from under the support cap. I think you should try to do that first and see if it seals. It is a fairly big job to remove and replace the radiator not to mention that it is very messy. If I were to do it again, I would seal it first but I never bothered to track down the leak since I had to address the oil leak also.