So, a few weeks ago i replaced all of the hoses on my cooling system, the thermostat as well, did a couple flushes, and filled up with the right coolant at a 50/50 mix. It now keeps perfect temp and gives me no issues. however....

i CANNOT get the upper radiator hose at the thermostat housing and the heater core hose on the firewall that's farthest to the passenger side to stop leaking. it happens after driving long enough to heat up and then turning the car off long enough to let it cool down (at work or overnight). i have re-clamped them over and over, tightened them too much, loosened them too much, and moved them back and forth all over to try to make them stop leaking. nothing is working. they are genuine mercedes parts/hoses but the clamps came from napa, but they are definitely the right size. none of the other many connections leak so i don't think it's the gear i used.

my question is: can i use some RTV or some other liquid gasket material and then slip the hoses on? will that work? if it does work, is it safe for the car/cooling system? i'm at my wits end here.

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1985 300D - 1984 Euro 280E AMG Clone (SOLD) - 1978 280CE (SOLD) - 1983 300D (SOLD) - 1981 300D (SOLD)

Clamps vary in their quality and construction. The size is only one parameter that is important. Just out of curiosity, what's the width of the clamps that you procured?

That leads me to believe there is a crack or two somewhere on the housing/s.
Is that heater core hose going to the mono valve?

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83 SD

84 CD

i'm not sure what the width of those clamps are, as i never even thought of that. they are just standard hose clamps, whatever width that may be, that were on napa's hanging hose clamp display. but the other ones are working just fine. i also brought all of the hoses into napa to fit them correctly to the right size (circumference) hose clamps.

the hose i'm talking about comes out of the firewall (from the heater core [i think]) and is shaped like the letter "U". there's another hose right next to it that connects back to a "Y" shaped metal tube on the fire wall. the one that is leaking attaches to the other side of the "Y" (and is not leaking on that end btw). it's leaking from the first side that comes out of the firewall on the passengers side. i considered the heater core leak as well but i actually went through 2 or three days worth of no leaks when last i rearranged the hose and re-clamped it. i actually thought i cured the problem until this morning.

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1985 300D - 1984 Euro 280E AMG Clone (SOLD) - 1978 280CE (SOLD) - 1983 300D (SOLD) - 1981 300D (SOLD)

Here are a couple of pics of my CD. You can see the clamps, original?

Attached Thumbnails

   

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83 SD

84 CD

Is it possible that the NAPA clamps do not have the capability of a socket drive?

The M/B clamps are not all that wide and they need a lot of clamping force. Hence the need for the socket drive.

in the pictures provided (thank you), the hose at issue is the one right in the top middle in the second picture and in the first picture, it's the one coming up and over the top of all of them. yes, those are the original mercedes hose clamps. i got rid of those with the hoses as two of them broke from rust a couple of months ago and i figured they should all be replaced if that's the condition they're now in. they do look skinnier than the clamps that i bought....

the napa clamps ARE socket drive, and that has helped me to tighten the heck out of them. so tight that rubber is coming through the screw slits. before someone asks, they have NOT cut through the rubber or damaged the hose because of their tightness, that's not the issue.

if you guys think that the clamps really have that much to do with it, are there other styles/shapes/thicknesses out there? i only have a couple auto stores / hardware stores at my disposal, is there an online hose clamp shop? maybe with all the hassle that went into getting these on there in the first place they bent and are no longer holding an even clamp?

maybe i should pick up a couple extra new hose clamps from napa and try them out.

as you guys help me chase this one down, what are your professional opinions about the RTV if it comes to that?

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1985 300D - 1984 Euro 280E AMG Clone (SOLD) - 1978 280CE (SOLD) - 1983 300D (SOLD) - 1981 300D (SOLD)

The thermostat housing hose nipple is aluminum and they sometimes build up bumps of corrosion that will impede a proper hose fit. Check all the leaking hose nipples and remove any lumps.
My SDL had corrosion lumps on the thermostat housing and head hose nipple. I suppose they don't leak until you replace the hose since the buildup is gradual and the new hose does not conform to the bump as the old one did.

I couldn't tell or either missed it, but are these new hoses?? I kept having leaks on my upper radiator hose. Swapped in another used spare hose I had. It leaked too.
I installed a new hose and my leak has vanished!
I've had to replace a similar hose as the "U" shaped one you have on one of my 240's, so sometimes old hoses just cannot be sealed.
Of course all this is moot if you're using new hoses.
RTV ain't the solution, you will be just temporarily masking a real problem.....

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

are all of these corrosion build ups and bumps invisible to the naked eye? i'm serious because i don't really see any but if i'm not supposed to see them, if they are in fact tiny bumps, then maybe that is the problem.

yes, they are new hoses and don't have the years and years of stresses to create conformity to the metal hoses anymore, so jimmy's point might not be moot, it could be BECAUSE of the new hoses.

what if instead of RTV i get a strip of thinner rubber to wrap around the metal hose first before putting the rubber hose on? that way i could make a tighter seal? of course, it still won't seal if there are corrosion bumps......

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1985 300D - 1984 Euro 280E AMG Clone (SOLD) - 1978 280CE (SOLD) - 1983 300D (SOLD) - 1981 300D (SOLD)

On my car the corrosion bumps were obvious, you could have them on the underside of the nipples. Anyhow, if the nipples are clean and not deeply pitted the hose will conform to its shape.

alright, so i picked up a couple of new hose clamps and got to work after work.

the hose on the firewall: took it off and cleaned the nipple. no build up or corrosion or bumps, smooth and clean. possible warpage on the clamp, possible clamp on at an angle. put on a new one and tightened the heck out of it at hopefully a better angle.

upper radiator hose at the t-stat housing: noticeable gunk and build up. chipped it away with a razor blade and scrubbed it until it was much cleaner. put on a new hose clamp at a straight angle. refilled, burped, driven to temp. and now left to cool back down to find out in the morning if things are any better.

i was hoping for a more obvious discovery. we'll see.....

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1985 300D - 1984 Euro 280E AMG Clone (SOLD) - 1978 280CE (SOLD) - 1983 300D (SOLD) - 1981 300D (SOLD)

I would not use any RTV there. It can cause the hose to spit off the fitting when under pressure. Something like a hardening Permatex (#1, I think) would work better, but will make future service a nightmare.

You shouldn't need anything but the rubber inside the hose.

Is it possible that the wider-than-original hose clamp is overlapping the bead on the pipe? (Which is not to say that a narrow clamp could not do the same thing.)

that was my original thought that had me detaching and reattaching the hoses a bunch of times, trying to make sure the hoses were placed exactly right before the bead on the pipes. i'm pretty sure i covered all my bases there unless the clamps no longer clamp true all the way around. i'll be picking up a couple new clamps after work just to be safe with that issue.

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1985 300D - 1984 Euro 280E AMG Clone (SOLD) - 1978 280CE (SOLD) - 1983 300D (SOLD) - 1981 300D (SOLD)