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Re: 2017 GLS550 Coolant Leak

Posted: Mon Nov 17, 2025 8:36 am
by rpaoness
Unless I'm missing something they don't appear to have the coolant fitting.

Re: 2017 GLS550 Coolant Leak

Posted: Mon Nov 17, 2025 8:42 am
by kevm14
Ah you are correct. I never checked. That's pretty lame on their part. I rarely order from them. My last order was 1 year ago for an axle boot kit.

I can't tell if Warwick has it. Or my phone isn't showing the usual "In stock" type info.

Re: 2017 GLS550 Coolant Leak

Posted: Sun Nov 23, 2025 8:02 am
by rpaoness
The coolant fitting replacement was only a PIA because of access to the rear hose clamp. They left what I assume is a service loop in the 3/8" or whatever lower line that made that easy. All back together and no leaks with a couple hour pressure test.

I was going to change the oil while I have it in and on the lift (4200 miles ish?). Based on test-running with the hood open I believe I should do an idler bearing and I guess serpentine belt change shortly since I think it's noisy.

Re: 2017 GLS550 Coolant Leak

Posted: Sun Nov 23, 2025 8:05 am
by rpaoness
Oh yeah, replacement of the plastic cylinder head plug was really simple. Based on how easy it went in, I hope it doesn't leak/loosen again. Rubber seal molded into the old one seemed hard/old, so hopefully that's why it leaked.

Re: 2017 GLS550 Coolant Leak

Posted: Mon Nov 24, 2025 4:38 am
by kevm14
rpaoness wrote: Sun Nov 23, 2025 8:02 am I was going to change the oil while I have it in and on the lift (4200 miles ish?). Based on test-running with the hood open I believe I should do an idler bearing and I guess serpentine belt change shortly since I think it's noisy.
Generally spin them and listen for noise or spinning that isn't damped by bearing grease. I believe when I did the big one on top the new one wasn't any tighter so I guess you can't just go by "slop.". Noise is probably a better indicator. And it shouldn't spin endlessly.

Re: 2017 GLS550 Coolant Leak

Posted: Thu Dec 11, 2025 10:09 am
by rpaoness
Coolant leak returned. 2 weeks leak free, but leaking again. Reports are that it is from the same place. I wonder what I missed or screwed up.

Re: 2017 GLS550 Coolant Leak

Posted: Thu Dec 11, 2025 5:34 pm
by rpaoness
I'm not sure I'll have enough time in the morning to pull the faux-firewall apart in the morning to get a better look at it, but it appears that the plastic fitting-to-heater core hose may have some coolant soaking the reinforcing cords, which makes me think that that it's likely damaged from being yanked on. I'll see if New London has the hose (which hopefully comes with clamps? I didn't see clamps in the parts list?) Looks like it's also not too bad - $15 MSRP.

https://www.mercedesbenzpartsshop.com/o ... 1668300496

Re: 2017 GLS550 Coolant Leak

Posted: Fri Dec 12, 2025 12:15 pm
by rpaoness
And…. Not in stock in CT. New London thought North Haven had one but said to check because it might’ve been ordered for a job or 48 hour old status. North Haven said their computer showed one, but they couldn’t find it.

Re: 2017 GLS550 Coolant Leak

Posted: Sat Dec 20, 2025 5:38 pm
by rpaoness
Now that I finally got a chance to look at it, appears to be an unrelated leak. Small diameter cooling hose going to the drivers side turbo. Hose says Cohline 2075.55.0819/67, 10x17

I’m guessing it’s part of a line assembly that bolts to the turbo. Since I guess it’s like 3/8” on one end and 5/8” on the other, it will be hard to replace with standard hose. Looks like someone likely put an aftermarket hose clamp on the bottom end.

Re: 2017 GLS550 Coolant Leak

Posted: Sat Dec 20, 2025 6:06 pm
by rpaoness
I think 3/8x1/2 would work