What are my options to fix a broken banjo bolt that connects the block to the water pump through the U shaped steel line. The banjo bolt on the block side was welded. On 1/2 turn with little resistance and it sheered off. I ended up drilling it out in hopes of getting back to the threads but that thing was welded through and through. Now I have a bigger hole and a specialty bolt that has to be there, or does it? Can I plug it? Can I tap it with a bigger diameter thread and drill my own specialty banjo bolt? What can I do? Thanks

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1981 240D auto
1977 240D manual 300 Turbo swap
1983 300SD
1983 300TD Parts car

Im not sure of the area you’re typing about but I would tap it for pipe thread and install a hose nipple. Finish by running a hose to the pipe.

There is a “U” shaped 1/4” steel line as you look at the block from the front near where the head meets the block. It is attached by banjo bolts to the water pump. The line is a coolant line. Idk if it is a bypass line or if it is designed to cool the bearing of the water pump.

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1981 240D auto
1977 240D manual 300 Turbo swap
1983 300SD
1983 300TD Parts car

More correctly, the line connects the head to the water pump housing.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

I wouldn't plug it since that coolant flow must be needed. It is a small tube so maybe it is just to help sweep out trapped air. You would expect some get clogged by rust, so perhaps wouldn't be fatal, but google it before doing that.

It sounds like you buggered up the hole in the head. Unlikely the bolt was welded to the head, rather it probably corroded in the hole. If you can't get the M-B banjo bolt, similar ones are used on some brake calipers. There are also banjo fittings on your M-B fuel supply to the IP. To fix a buggered hole, look at heli-coil. A bit pricey and I have only used for SAE bolts, but should be metric ones today. I think there are 3 different pitches for metric bolts (coarse, fine, extra-fine), so measure carefully.

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

It sounds like stephenc1984 is talking about the water pump purge line. It allows the pump to purge air out of the head and a small amount of water to circulate when the thermostat is closed. I would turn up a new banjo bolt on the lathe (may have issues making the hole large thru the banjo to fit the larger bolt), or install a metric Helicoil.

A bypass thermostat is never "closed." Coolant circulates any time the water pump operates.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Aside from the dealer, banjo bolts should be available from industrial shops.

I was thinking I could just take a standard bolt. Drill out a portion of the bolt and tap the hole on the motor to the size of the bolt and call it good.

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1981 240D auto
1977 240D manual 300 Turbo swap
1983 300SD
1983 300TD Parts car

I believe this might be too complicated if you are not used to drilling and tapping stuff.

The one advantage you have is that the threads hole dose not have to take any load. It just has to hold the Tube on.

If the hole is drilled out larger now you could rethread the hole for a larger bolt. Preferably brass or Aluminum (yep a local industrial supply has some aluminum bolts). Although it could be done with steel you want a bolt that is easy to cut and file down.

Screw in the new Bolt with slow curing JB Weld Epoxy. Let that cure and cut it of and file it flush with the with the cylinder head. After which you would drill a hole in the metal and tap and thread it for the new Banjo Bolt (likely metric).

The new tapped hole in the head would have to be large enough so that the bolt your going to cut off leaves enough metal that it can be drilled and tapped for the new banjo bolt.

Another problem is that the banjo bolt hole has to be drilled fairly straight in or the copper crush washers are not going to seal it.

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84 300D, 82 Volvo 244Gl Diesel

This is what I am referring to. Thank you.

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1981 240D auto
1977 240D manual 300 Turbo swap
1983 300SD
1983 300TD Parts car

It's not just drilling a hole. The bolt has to be turned to allow a flow path around the ID of the fitting. $5 at industrial supply, no tears.

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E in the coolant diagram is listed as a vent line.

Unfortunately I know of no one that has written about your specific problem.

However, I am going to stick my neck out and speculate that it does not seem to do much as far as cooling goes. If you otherwise got the air out of the system one would think the cooling system would function OK without it.

But, if you plugged both holes off you are clearly experimenting.

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84 300D, 82 Volvo 244Gl Diesel

I couldn't conclude that the passage created by that bolt and line are not needed. Back in the 1960 and earlier, thermostats would prevent all water flow until the engine was warmed enough to open them. Many cast iron heads cracked from cold water being dumped on thin, hot cast iron.

It seems MB engineers may have included at least two outlets to let small amounts of water circulate when the engine is running whether or not the thermostat is open. An engine might last a bit longer before a head cracks from heat if the thermostat freezes closed.

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84 300SD
85 380SE
83 528e
95 318ic

I found a place which referred to it as a bleed hole to evacuate air from the water pump. I might have the words wrong but I am pretty sure I would not try to eliminate it. I'd put it back stock.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.