I’m about to tackle the oil cooler seals. Any recommendations on “while you’re in there” do these things? I’m thinking of replacing the thermostat, idler pulleys, belt, belt tensioner, and the power steering reservoir and seal.

Also is it worth getting OEM parts or are aftermarket parts from FCP okay? I’m trying to keep this car another 10+ years so I want to get the maintenance dialed in.

 

It depends on when various items were last replaced.

If you replace the thermostat, you will almost certainly have to replace the upper radiator hose, unless you can match the o-ring.

The thermostat is a long-lived item, with the common failure mode being sticking open. It is a wax motor, and the wax is pretty good about forcing the thermostat open but not so good at pulling it closed. So it typically can be ignored until the motor does not adequately warm. Given how the dash gauge masks the info, even the slightest lack of warm-up should be heeded.

I have not done it, but my impression is the oil cooler seal is not invasive surgery, so it probably ought to be performed in isolation.

Your determination to help your GL live long and prosper is admirable, but keep in mind, you can put thousands of dollars into it and lose it all tomorrow should a rock fall from the sky.

 

If you have some mileage, the PS reservoir makes sense since it needs to come off to get at the cooler, there is a filter built into it and it is reasonably cheap. Make sure to bleed properly after you put a new one in or replace the old one. (Fill the reservoir and turn the steering wheel back and forth with the front tires off the ground while checking fluid level and adding as needed until you stop seeing air/bubbles in the reservoir) I used the oil cooler seal FCP sells and so far no leaks after a year and 15K miles on my ML. It is an easy job once the PS reservoir is out of the way - just make sure to get all the remnants of the old hard seal off before putting the new one in.

 

Yeah that’s true. I’m doing all of the work myself so it’s not too costly. To remove the oil cooler assembly you have to remove the thermostat and the belt tensioner to get to the bolts for the oil cooler. Since I’m removing them anyway I’m thinking of just replacing them. But yeah if the parts are fine I maybe should just leave them alone. The whole “while your in there might as well do this” gets me most of the time. 😂

 

Do you recommend doing the oil cooler assembly gasket as well? That one requires more work. It does look like it’s just the cooler itself that is leaking but if that gasket is bad then I’m assuming the other one is on its way out?

 

on what? 350 or 450/550?
answers depend

 

2011 Mercedes gl450

 

I just did the one that is sandwiched between the plate the cooler mounts to and the cooler itself you get access to by removing 5-6 torx head bolts. The other one hasn't leaked on my former GL or ML.

 

good time to replace the engine oil filter housing gasket as well, and two idler pulley, drive belt tensioner. and check radiator for possible leaks. and replace coolant if its time.

 

Yeah, basically everything in the upper right front quadrant… It would be good to have a go with the O-ring for the power steering reservoir while replacing the reservoir itself.
all serpentines and pulleys with quality, pulleys and bearings… That’s all I would do with that while I’m in there.

I would not touch the thermostat if it is a factory MB unit that is operating perfectly.

I was relieved to hear that wasn’t a diesel, at which point the while you’re in there becomes everything.

 

don't replace anything until it's broken. its a habit that costs you money and doesn't let you appreciate the natural lifespan of your components for science reasons IMHO. i replace outer tie rods or a singular pair of control arms at a time on my personal vehicles.

If you WERENT doing the labor yourself then hell yeah spend it up and make it good for the long haul, but honestly these items all have vastly different service intervals and its really nothing to go back in to tackle those things one at a time... particularly the front drive stuff which goes out pretty far.

also if you want to save time/headache since theres an internal check valve which isn't quite serviceable, just buy the oil cooler assembly, you should have a fresh filter, and gaskets that come with that.