Mystery coolant leak

Cummins has a lower engine gasket kit which is part 3802375 which sells for $519.10. That is every gasket and seal below the head. That is a complete rebuild kit. The head gasket and exhaust gaskets are not included in that kit. Standard head gasket is part 3283333 (.25mm oversize is 3283336 and .50mm oversize is 3283338), valve cover gasket 3930906, oil filler cap gasket is 3936876, intake manifold gasket is 3938153, aftercooler inlet gasket is 3914856, exhaust manifold gasket is 3927154, turbo inlet gasket is 3709861, and turbo oil drain gasket is 3765575. All the gaskets and seals in that big kit can also be bought individually. There are 38 different parts in that kit. There are 2 different filter head gaskets in the kit depending on which block arrangement you have. Early engine types use gasket 3929792 shown here.

Later engines use gasket 3942915 shown here.

Here are all the gaskets in the big kit.
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Have fun.

There was something that bothered me about that head gasket. There are normally metal tabs the join the rings to seal the cylinders. Also metal down one side and on the corner. Here's a good video showing a good quality and a really crappy head gasket.

No, that's not how it would work. With the aftercooler the air is cooled down to that point or a bit lower. The cooled water coming into the aftercooler is coming direct from the radiator which is lower than 180 deg which is the internal engine water temp. If you were running a separate radiator on the aftercooler it would be even more efficient. The heat exchanger mounted on the intake is the defining factor on that. Cummins offered 2 different heat exchangers on the 4bt. The later model was probably a bit better than the early one but still used engine coolant. Not the ideal system but better than none at all. Most diesels use an air to air intercooler mainly because it's cheaper, not better. The newer Ford diesels all use the water to air type. When you look at that system, the aftercooler radiator is huge. Around 4 feet wide and literally bigger than the engine cooling radiator. What is creating all the heat in the system is the turbo itself. When you compress air it gets hotter. Those silicone connecting hoses on the system are not for show. They are rated to 500 deg F and air temp can easily pass 300 deg F. Higher altitude areas make it even worse. It would be interesting to have air temp sensors in a turbo system, one reading temp coming out of the turbo and one reading temp at the intake manifold. Those gauges exist in various grades. The really good ones tend to be kind of expensive like in the $300 area. Good things are seldom cheap.

On your turbo plumbing, have you checked the clearance between your air intake and the oil filter? Going to be close if even possible. You'll need an air cobra head intake hose but yours is 4" like the HX35W. See photo below. I suspect you may need a remote oil filter. You'll just have to check and see. On the intercooler pipes, you can go smaller. The standard outlet elbow for the Super 30 is 3". There may be a 2.5" but it's not one we ever see. The standard 3" part number is 3918685 but there is a part 3918684 showing to be 2.5". Of course your can just use the 3" and a necked down coupling hose. I'd try to keep the pipes 2.5" if possible. What part for the oil drain are you looking for? If it is part # 4 in this diagram that is part 3903744. Cummins charges $56.91 for it but you can find it for near half that price.

If that is a standard HX30W/HX35W flange then it's a hair over 3". Amazingly, Cummins makes that part you're looking for which is 3910990. See photo below. That part is around $50 or so. I'm sure there are some aftermarket parts out there that are cheaper but this is one option. Are you needing a tighter bend than what you have there? That one looks to be about as tight as you can make it. That part is a half Marmon flange and you could make it with a lathe. Just use the old flange for dimensions.

Part 3959261 is available. Just don't look at the regular vendors who have that thing priced into outer space. Here's a used one on ebay for $49.99 including shipping. Cummins Part # 3959261 Connection Exhaust Outlet Elbow Pipe | eBay Here's a brand new one for $49.95 or best offer. Genuine Cummins Exhaust Outlet Connection, pn 3959261 | eBay Have also seen used ones on some of the truck salvage yards. Another possible might be 3910992.

Here's one of those on Amazon for $64.60. https://www.amazon.com/Solarhome-3910992-Connection-Exhaust-Cummins/dp/B08D9C4GRC
Here is yet another possible with part 4939408. One thing you'd have to watch on this one is it requires a larger exhaust pipe. Was originally used on a ISBe6.7 with a reverse mounted turbo.

Would probably require removing that bolt stud on the side which this guy did. Here's a photo of one on an engine.

For 3" probably none of them. Here's 3959261. It's about as tight as you can get and I'd say it probably needs about 3.75"-4.00". Have to figure the flange alone is a hair over 3" and then another 1/2-3/4" spacing for the clamp and a little more maybe for that bump sticking out the back. Only a true cobra head might fit the space and it can't be less than the diameter of the flange. Pacbrake has some cobra heads but their smallest is 3.5" so that's no help. There's just never been enough demand for anyone to make a 3" unit. Although you hate to make changes, your best solution would be a different exhaust manifold. If you don't have hood clearance for the top center mounted turbo like shown in post #4, then the cut down 6bt manifold might be the answer. When you go from a H1c turbo to the HX30W the tail section gets about 1.5" longer.

High EGT usually comes from too much fuel and not enough air to burn it. People often keep turning up the fuel in hopes to get more power and often just get more heat. A well balanced system usually peaks in the 1000-1200 deg area. The 1000 is more desirable. Another factor that can affect EGT is altitude where you are at. At higher altitude your air/fuel ratio is not the same. With a diesel, they run cooler the leaner you run the fuel. Exact opposite of a gas engine. Also, injection pump timing will affect EGT. Advancing the timing usually lowers EGT and increases power. Just can't get too aggressive with that or you may blow the head gasket. Also, the engine will be noisier with advanced timing. I would think 35 PSI would be the max limit on a Super 30. It may go higher but you start to get off the map where it makes the best power. Member Dougal can tell you about what boost level you need to produce certain power levels. You mention wanting it to spool fast. A Super 30 will spool slightly slower than a standard 30 but not by a lot. It's just a matter of the fact you're spinning a larger compressor so it takes a little longer. It's not like the guys trying to run an HX35W and it a dead dog on the bottom end. All it's power is in the upper RPM range. You have a turbo with a turbine housing that is twice as big, a larger compressor, and 1/3 less exhaust to drive it. Doesn't take a PHD in physics to see that doesn't work well. When it comes to wanting the best of all worlds, twin turbos are probably the best solution.