My car 1987 300D had a near death experience last week. It was turning 400k miles on the way back from San Francisco. A milestone reached so to speak. However, when it was climbing Los Angeles National Forest the radiator neck snapped and lost most, if not all, coolant. It overheat big time. Luckily we were near the top of the climb and limped to

Fort Tejon State Historic Park

https://g.co/kgs/TjZDaU

The break wasn't a clean break and I couldn't attach the upper hose back on. I had it tow home. Ordered a new radiator and car is now back on the road. So check your radiator and change it out if necessary, plastic radiator is prone to breakage.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Yes, plastic end tanks on radiators (and intercoolers) don't make sense for parts longevity.

My new DD, 'Kjetteri', developed a mystery coolant leak with a tiny bit of foam in the coolant expansion tank.
Turned out to be a cracked plastic radiator nipple, and not a head gasket failure.

On Monday morning I bought a 3/4' X 1/2" PVC coupling and 2 oz of epoxy putty to repair the nipple in the afternoon after the car was cold.

On the way to work, steam started wisping out of the left front of the hood, so I did an emergency roadside repair.

The plastic end tank still leaks a tiny bit of steam from a crack between the top overflow nipple and the top hose nipple.
A replacement radiator will be installed...if I end up keeping this 'Heresy'.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

If you need a hand with anything I’m not too far away. I can grab a radiator from my 94 and bring it to you.

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1993 e300
1995 e320
1994 e320
2006 s500 4matic
2004 Jeep wj overland
2001 Ducati 748
2004 Honda shadow aero

I just had a coolant bottle explode.
No excessive pressure, possible prior trauma from an overheat long before I got the car, but has been fine for years now.
I went ahead and replaced the overflow tank and cap just in case, car is running a-ok again, incredibly it blew out in my driveway right as I got home one day.

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1982 300D (w123, "Grey Car")
1982 300D (w123, "Blue Car")
2001 Ford F150 "Clifford" (The Big Red Truck)
1997 Dodge Ram 2500 12V Cummins
1996 Dodge Ram 2500 12V Cummins
Previous Vehicles:
1995 E300D, 1980 300SD, 1992 Buick Century, 2005 Saturn Ion

Mine blew on my 83 300D after only 3 laps of a track, then I drove it like that for like 3000 miles including a giant roadtrip, before replacing it with the new style with the wonderful baffles and the level sensor blockoff

It happened to me when I used to own the w126 1989 300SE.
Luckily right before entering the freeway bridge entrance on Turkey day!
I stopped immediately.
Fetched some water from a near by store.
was able to keep the neck closed with the 'mechanical' hose pressure,long enough to drive back home. (maybe 6 miles).
Did not overheat.
I think I saw the steam just before entering the freeway... long ago....

replaced the thermostat cover with an aluminum one, the original was plastic, and also replaced the radiator because the neck edges were deteriorating.

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

It happened to me and about a year latter it needed a head gasket and the head flatted. That's one pattern I've seen several times before.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Glad you have it running again, and it wasn't too catastrophic.

For those with W123 300D, new radiators are now affordable. I got one for $130 vs used to be $350. That solved the overheating in my 1985 300D after trying many other things over years, even another used radiator first left sitting with citric acid for a week. That climb on I-5 N out of the L.A. Basin, on a >100 F day, is where I have heard new car coolant designs are verified. If you go up the grade slower, that will reduce the horsepower output of the engine, if fighting an overheating issue.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

This.

When needing to verify work I’d done to my cooling system, this was the proving ground.

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1981 240D 4sp manual. Ivory White.

Uncle Kent sells a reinforcement kit which is quite effective at preventing this exact issue.

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Why I will never do business with "DieselKraut" again

http://www.peachparts.com/shopforum/mercedes-benz-used-parts-sale-wanted/378935-why-i-will-never-do-business-dieselkraut-again.html

MS in Bellingham has issued a warning on this and recommends a copper sleeve inserted inside with epoxy to reinforce it. He sells the components. it is a known problem and why these car companies think that plastic radiators caps are acceptable is beyond me.

You can reinforce it all you want but the breakage is at the base of the neck and took out a bit of the body itself. Basically no 'neck' left. The kit would not help. The breakage is a crapshoot thing so you take your own risk.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

We have read here that the upper plastic nipple on the radiator cracked at the base of the neck and another person said it cracked further out. I suspect unless Kent's idea of a copper sleeve/epoxy reinforcement would help if for no other reason than it spreads the stress out all over and around the hose nipple. I decided to do my own version using the MS method. I used powdered copper as an epoxy thickener which gives astounding strength probably better than the powdered aluminum of JB weld. I also cut pieces of graphite cloth/epoxy around the base and up to the flange for the hose, carrying the load almost an inch on to the radiator cap housing all around to a thickness of 3/16-1/4". This gives what amounts to an epoxy gusset. Curious that nobody mentioned failure of the lower radiator hose nipple, perhaps because it probably runs a little cooler?

This is my take. You can reinforce it all you want but it doesn't resolve the fundamental problem of plastic fatigue. The breakage can be at the neck, at the neck base or thereabouts. You may end up with no neck to speak of. This is what happens to me at the most inopportune time. If the car is a keeper then just replace it for not so much money. I have a #14 head on the 87 300D so any overheating is a death nail. If you want to do any preventative maintenance then this is it.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.