Cummins fuel block

Some probably most Cummins 6BT series engines have a fuel block which as I understand it is a block of metal with channels bored into it with fittings where fuel enters and exits the engine. It also has ports for fitting fuel and oil pressure gauges and probably some other test equipment. There appears to be up to 8 ports and in my case several are plugged because they are not needed. This engine is a reman, a year and a half old. Fuel has been leaking from one of the unused and plugged ports since it was installed. I didn't realize fuel was coming from one of these ports until I finally decided to hire Cummins to fix the fuel leak knowing I still had 6 months of warranty left.

Because this is a reman long block engine several items were taken from the old or core engine including the starter and fuel block. So the fuel block because it is not part of the reman is not covered under warranty. The location of the fuel leak plug is very difficult to get to requiring a partial disassembly of the engine, mainly removal of the after-cooler and probably the fuel cooler. Cummins is estimating 8 hrs to fix this which is nearing $1000.

I have removed both the fuel cooler and after-cooler several times and it is a real pain. 8 hrs is a bit of a stretch but it is a pain. The boat is 1000 miles from home and the mechanic that installed the engine is not available that far away. I have very limited time to work on the boat and with a car rental for a couple of days it would cost me a couple of hundred bucks if I do it my self, which I just really don't have the time to do. On top of that I just recently developed a pinched nerve which makes it very painful to reach down into the engine. I'm hopeful the pinch nerve pain goes away soon, most do.

I'm just ranting but a lesson learned. I should have fixed the fuel leak right after I noticed it. We left on an extended cruise and didn't want to wait.

Can you snug up the plugs? I think they are all just NPT.

Ski in NC said:

Can you snug up the plugs? I think they are all just NPT.

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Yes I think so. From the cell phone pics the mechanic took it looks to me the plugs all accept a 3/8" drive socket. The problem is I can't get a socket wrench on the plug without removing the after-cooler and fuel cooler. At least that was what I was told. Thinking the fuel leak was under warranty I did not look carefully where the plugs were located when the Cummins mechanic was at the boat. I am just taking his word for it.

You mean a square drive? How about a short piece of key stock and a 3/8 open end wrench. Maybe you can squeeze that in there???

Having to remove the fuel cooler to get at the fuel/oil block I can understand (you might want to consider not putting it back on afterwards....only needed if your fuel tank volume is so small that the returning fuel would heat it up: see BoatDiesel for more or ask Ski). But I cannot image why removing the aftercooler should be necessary. I've taken my fuel/oil block off (6BTA 5.9) and didn't need to go anywhere near the a/cooler.

On several I found the fuel hose end fittings are on an adapter that screws into the npt port. The adapter itself is loose in the npt. Have to break the hose fitting loose from the adapter, then snug the adapter, then snug hose to adapter.

Rare for the plugs themselves to leak.

Thanks guys for all your help. I finally got the Cummins mechanic to send me the pics he took.

Thinking the engine was under warranty I did not look for myself where the leak is or how difficult it is to get to. I am just taking the mechanics word when he said about 8 hrs labor and removal of the after-cooler was necessary.

Looking at the pics I don't think the leak is due to a hose attached to a fitting as suggested by SKI. I'm going to look for myself before authorizing Cummins to do the work.

Aqualbelle; good to hear you didn't have to remove the after-cooler to get to the fuel block. But as I recall the after-cooler will need to be loose in order to remove the raw water hoses to allow space to remove the fuel cooler hoses.
Concerning the wisdom of removing the fuel cooler; I've read Tony's suggestions on this, and I have no doubt that he's the expert. The only thing I can say about this is that his experience in the San Diego area with water temps rarely above 60 degrees may be different than mine where the water temps are rarely below 60 degrees. None the less I won't remove the fuel cooler until the engine is out of warranty.

jleonard; great idea about the key stock, it might work, I'll check when I get down to the boat next week.

Thanks guys for your comments. Below are the pics, additional comments are welcome.

Geez Tim...where's the leak?? At the worst, Ski's right as usual...not the fuel block plugs but if anything the fuel hose adapter connection on just one, maybe? (And no, the a/cooler doesn't even need to be loosened off to remove fuel or raw water hoses.)

Looking at the 3rd picture you can see a drop of fuel about to drop from the fuel block and it looks like it originated from the plug closest to it. The first picture also shows fuel seeping from the plug.
When the pics were taken the engines had been previously winterized and not run for about 7 months.

Last season it leaked enough to fully saturate 2 diapers after about 25 hrs of run time.

First pic, middle hose: Looks damp to me where adapter screws into block. Note pic is oriented funny, the surface where the square socket plugs go in is actually the bottom, confirmed by seeing edge of oil pan rail. So anything moistening the block will gather around that plug. Gravity thing.

I'd snug that middle hose adapter. While there put a ratchet wrench in the plugs and snug them too.

Greetings,
Mr. t. OK, so $1k for Cummins to fix it. Sounds like it would be cheaper to fly the mechanic who put that block in place to come and fix his mistake.

After giving this some thought I think SKI is correct. The fuel is probably coming from the adapter or a steel hose fitting that screws into the adapter as he suggested, not the plug. I did not notice fuel leaking from the previous engine and none of the plugs on the fuel block should have been touched when the fuel block was transferred from the old engine to the new one. Only the adapters would have been reattached to the new engine.

Since I haven't look at it carefully I don't know if the fuel cooler needs to be removed to allow access to the fittings on the fuel block. But if so it seems I remember the a-cooler needs to be loosened, not removed to allow space to remove the hoses from the fuel cooler. The hoses on the fuel cooler are restricted from moving by the fuel lines on one side and by the a-cooler on the other. Am i wrong?

I've read Tony's opinion on the fuel cooler, SKI what's your opinion operating these engines in summer on the east coast w/o the fuel cooler?

Something about that middle hose doesn't look right to me in the pic. Looks like the fitting on the hose is not seating with the adaptor all the way . This hose has a crimped on fitting and the the other hose has a reuseable fitting . Looking from the top the reusable looks seated better . I think these are probably female jic fittings . Could it be that crimped on fitting is not the right fitting and is not sealing with adaptor plug and never has ? I know sometimes threads will match and get tight but not seal on the inside surface.

Suggest you try your questions on boatdiesel.com. You will get experts, probably the best there is on your Cummins helping you solve the problem. Nothing against the folks here.

Tim, I had a similar leak from my fuel pump on my stbd Perkins. I tightened the fittings, but couldn't seem to stop the seepage. Finally, I cut strips of the diaper and attached then carefully around a couple fittings at a time until I found the exact one that was leaking. It was not near where the fuel drip was visible. Once identified, tightening it was easy. It only took a small tweak to stop the seepage. Hopefully, you'll have the same luck.

Where did I just see this same problem written up? Steve D'A or Tony Athens article?Dry the block with paper towels, short piece of square bar stock and wrench for the square drive plugs. for $1K+ I would try to find out exactly where the leak was first.

I think his issue it is outboard on port engine and very tight access.

Greetings,
Put some fluorescent dye in the Racor to trace the leak.

Foot powder! Comes in a spray can and sticks to things, smells nice and fuel leaves a track in it. Or, take some of those blue shop towels and wrap them around the lines or use masking tape and tape them over suspect parts.

Thanks guys for all your input. Ski is right, very tight access, only about 5" between engine port side and fuel tank.
Al, I was thinking of that exact same idea. I think Ski is correct in a previous post where he identified the leaking fitting.

The real issue here is my pinched nerve. It hurts like hell to reach down into the engine. I've been dealing with this for 3 months. I can't take any strong narcotic type pain killers because I'm on flying status and that's a big no-no with the FAA. Anyway I'm going to a pain Dr. Tuesday who will inject a steroid and will hopefully give me some relief. I've already had 2 injections from a Orthopedic Dr with no relief, but he said the pain Dr is more precise in locating the nerve and injecting the steroid.

If the injection works I'll be down at the boat next week fixing this issue myself. Like they say getting old is not for sissies. I'm 64 and in otherwise great health and shape, I don't consider myself old.

fryedaze said:

Suggest you try your questions on boatdiesel.com. You will get experts, probably the best there is on your Cummins helping you solve the problem. Nothing against the folks here.

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Thanks, I did. Tony came back with some great pics of the engine w/o the fuel cooler and a modified fuel block. I'm not going to remove the fuel cooler just yet, but will consider it when I get the boat back home to Tampa next year. It will be due for after-cooler cleanings, and that would be a good time to remove them.

Once I learned to lift the floor on my Carver I did it whenever things were too tight. Took advantage and did filters and careful inspection at the same time.

If the plugs are on the bottom of the block I think Ski has gotten it right. One of the adapters threads is wet with fuel. Leak is where you find fuel at the highest point. Doesn't look like the plug is leaking it is just a point where fuel is puddling along the way.

timjet said:

Thanks guys for all your help. I finally got the Cummins mechanic to send me the pics he took.

Thinking the engine was under warranty I did not look for myself where the leak is or how difficult it is to get to. I am just taking the mechanics word when he said about 8 hrs labor and removal of the after-cooler was necessary.

Looking at the pics I don't think the leak is due to a hose attached to a fitting as suggested by SKI. I'm going to look for myself before authorizing Cummins to do the work.

Aqualbelle; good to hear you didn't have to remove the after-cooler to get to the fuel block. But as I recall the after-cooler will need to be loose in order to remove the raw water hoses to allow space to remove the fuel cooler hoses.
Concerning the wisdom of removing the fuel cooler; I've read Tony's suggestions on this, and I have no doubt that he's the expert. The only thing I can say about this is that his experience in the San Diego area with water temps rarely above 60 degrees may be different than mine where the water temps are rarely below 60 degrees. None the less I won't remove the fuel cooler until the engine is out of warranty.

jleonard; great idea about the key stock, it might work, I'll check when I get down to the boat next week.

Thanks guys for your comments. Below are the pics, additional comments are welcome.

Click to expand...

Plugs are 5/16" square drive. Just trying to tighten them runs the risk of splitting the aluminum block they are in. If you go to the trouble of stripping down the engine to get at it, you should get the Seaboard Marine kit and do it for good.
There certainly are thread sealants and plugs that will do this job correctly. Makes you wonder why Cummins didn't use them reman or new.