M916 NTC-400 Coolant Leak Help

[Castle Bravo]

So I've been chasing a problem for a while on the M916.

Back when I changed the thermostat, the water bypass tube that connects the water pump to the thermostat housing (#11) started leaking. It is kind of an odd setup - there is an o-ring (#16) that seals the tube (#15) to the water pump and a sort of half clamp (#21) that holds it in place. As soon as I turn on the engine and pressure builds, coolant starts leaking through the connection. A new o-ring did not fix the problem, I may try to apply RTV to the o-ring and surrounding area to see if that will seal.

It is also very, very difficult to get the hose that connects the tube and thermostat housing (#11) in place with the o-ring on the tube. Several times now, I've cut up the hose and o-ring while trying to get everything in place.

Anybody else who's worked on the NTC-400 run into this or have any tips?

 

[goodguyzy]

The only thing I can suggest is using silicone grease on the o-ring, helping it to seat right.

 

[LanceRobson]

You might try calling a Cummins shop and see what they say. The Cummins website show several in AZ.

Lance

 

[BigWill1985]

I recommend that you check to make sure the seating surface is true, without any pits or warpage. That tube shouldn't have a ton of forces working against it, so the U clamp should work fine at holding it in place and sealing it. Clean up the seating surface below the tube (where the o-ring sits) and make sure it seats perfectly flush on all sides. You should be able to use emery cloth and a block of wood to true it up and make it completely flat. If you're having trouble with the o-ring pinching or moving around on you, use a dab of wheel bearing grease at 4 points in the o-ring groove (90* apart on each). That will help hold the o-ring in place. Also, put a very thin film of grease on the block below the tube so you can slide the tube into the hose, and swing it into place on the bottom without disturbing the o-ring. Grease works wonders on these situations.

I hope this helps you!

~Will Courtier~

 

[rangereter]

These are very good configurations for the water plumbing when in tact (undisturbed), most diesel engine builders do use this type water/coolant connections. Make sure that you use small diameter wire wheel brush in the tube bores with either a drill or die grinder, and make sure that you wire wheel the tube o-ring grooves. If the rust pits are too deep, then you are asking too much from the o-ring seal to fill, and then the part should be replaced. You can't go wrong with liquid dish soap for lube on water connections during assembly. If you are having trouble making the connections, that usually means that one of the housings needs to be removed to facilitate assembly.
Regards, Bob

 

[Castle Bravo]

I managed to get it all together today. I'll let it cure for a few days, replace the coolant, and then try it out.

 

[powersmoke18]

I usually use wd40 spray the hose down so it will slide all the way on the pipe. be sure you are using the correct oring to! they tend to be silicone when it comes to coolant. that connection is famous for leaking, dirt and other debris get in there and cause all kindsa pitting and what not. could also have a crack in it!!

 

[Castle Bravo]

Well, after getting it hot several times, it seems to not be leaking anymore! All of the parts could be sourced through Cummins, still. I did not have to replace the tube itself, but that was the next step. It was about $60.00 if I remember correctly. The o-rings are a few bucks each.