danmm7

Car is 2003 SL55 with about 140k miles.
Drove the car today, parked it on the driveway and noticed a small puddle under it, on the driver side, by the bumper. It's leaking coolant from somewhere. Under the hood, I could see dry coolant residue and drops in the lower driver side corner of the radiator area. I removed the plastic panel under the radiator, but I cannot see where the leak is exactly yet, since it was getting dark, there were lots of coolant stains, and I had limited access/visibility. I am not sure, but I am assuming it's a slow leak from the side of the radiator and the cooling fan has spread the antifreeze all over the place in this general area. I don't see a leaking hose, so it must be the radiator itself. Not only that, but I have no idea how old is this radiator either. It may be the original one.

1. Aside from the radiator, are there any other known coolant leak prone areas on the driver side? Anything else i should check before i order a new radiator?

2. How much of a pain is to replace the radiator on these cars? I've replaced radiators before on some older trucks, Lexus SUV and my Audi S4. Any specific tricks/issues with the setup on the SL55?

Thanks in advance!

Sozo

Check the the spot where the upper radiator hose connects to the radiator, about mid way down the side of the radiator on the driver's side. The hose fitting at the radiator is plastic with a rubber o-ring inside, and where it fits onto the radiator is plastic as well. Mine is an '07 SL550 and I had to change the hose recently (because of a failure where the fitting meets the engine which is metal), When I removed the bottom part at the radiator, I found previous owner had used some kind if sealant where this fitting met the radiator (likely because of leak there as you may be experiencing). Also I noticed the old o-ring inside the fitting (comes installed with the hose) was quite flat and obviously old (again likely cause behind leak).
I was very fortunate to be able to remove the hose where it meets the radiator. There are some horror stories on this forum (and you tube videos) of how hard the hose is to remove, and the fragility/issues because it is plastic, so you want to be careful how you try to remove it and how much force you use so as not to break anything. If you attempt it you want to use some gentle, even pressure at different sides of the hose (I used a long wide screwdriver). Also note that the fitting does not twist off as it fits straight on and slots in over a few tabs.
Anyway, an OEM hose can be found for approx. $60 new at a parts store (not eBay or MB), so it was a cheap fix. Lastly, the hose comes as one piece despite several hose/clamp connections, but at that price for the whole thing I didn't take risks taking that apart and risking being unable to out it back together properly as this is a high pressure component designed and put together a certain way,
Good luck!

sivikvtec

On my SL65, I had to remove the bumper to get access to all of the bolts on the front and on the lower drivers side of the radiator.

SL55 might be different, but just something to look out for.

danmm7

I think you are right. I did inspect the radiator and hose in more detail today, and it looks like the dried coolant stains originate from around the upper radiator hose connections. Unless there is an actual crack in the radiator plastic right there, it must be the hose O-ring seal leaking under pressure. The leaks started there and the liquid when down, the fan likely spread it around and this is why I have a bunch of dried off coolant stains everywhere in the bottom part of the radiator area.

I ordered a brand-new OEM hose and waiting for it.

brucewane

On my SL600, that hose is held on the radiator neck by a wire retainer clip that you pull down towards the ground to release - you can't see it from the top. I got to it from under the car using a pair of long compound needle nose pliers. Since your engine is smaller, you may have enough room in your car to get your hand in there.

vkovaler888

I had exactly the same problem and started with the O ring first, then the hose. It still leaked from underneath the hose. I ended up with new radiator and never had the problem since. I also had 07 SL550.

Sozo

I think the hose on the SL550 is the same. I took pics of my old hose as this may help:

Here is the hose I removed. You can see the red sealant that had been applied. Also the clip brucewane mentions is shown lowered (to remove the hose) and the notches at top and bottom I mentioned showing this hose cannot be twisted off.

From the side you can see how the clip opens. Note the clip does not need to and should not be removed. It lowers and then rests agains a stop on the hose.

Now it is in the closed position where it rests in the closed 'notch'. It's important to make sure the hose is on all the way on the radiator connection as the clip slips onto a groove there, with the wire from the clip securing the hose in place over it.

One last look at the inside of the hose with the clip in the closed position, so you can see how the clip locks into the groove over the connection to the radiator. You can clearly see here the o-ring (and the sealant that was used)

Hope this helps!

danmm7

This is useful. I can see the clip on my hose clearly, and i should be able to reach it just fine from under the car. I just need to figure out a way to gracefully disconnect the old hose from the radiator without damaging the radiator itself. Hopefully it's not stuck too much. Who knows if this is the original hose or not and when was the last time anyone touched it.

Obviously, I would have to drain the coolant from the radiator first and refill after I am done. Any tricks when it comes to burping the system?

I have a vacuum coolant refill device, just not sure if it will work well on this car, given that I also have the supercharger cooling circuit involved. I still havent separated the SC from the engine cooling. I wish I did it earlier. Perhaps now is the time to split them.

Sozo

So in my case I drained fluid from the bottom of the radiator (red plug) until I saw it got very low in the reservoir tank. At that point I knew any remaining fluid would be below the line where the hose connected. After replacing the hose I just filled coolant in the reservoir until it reached the correct level. I did not use any refill device. I believe the system in this car is self-burping or bleeding of air (at least in the '07 SL550). I did squeeze the top hose a few times once I started the engine but don't know if I needed to. I have since driven the car many times, including at highway speeds, with the car at temp stable at 90c.