cooling system capacity

My gut tells me do not use PVC pipe for wet exhaust.
Sounds like something an insurance company would have a fit over.

I would only use certified wet exhaust hose, fiberglass tubing intended for wet exhaust, or copper pipe.

My boat has copper pipe for generator wet exhaust.

I think the 71s do not require anything other than standard coolant because they have dry liners.

The 71's have dry liners yes. So coolant is more flexible. I still would use the mtu/DD factory powercool antifreeze. DD also sells a flush additive, which I'd also recommend. Drop the old coolant, fill with water and coolant flush additive, run engines for 30 minutes, drop water/flush, then I'd repeat the process with straight water and then drain and add fresh DD powercool antifreeze. The factory stuff is reasonably enough priced that it doesn't pay to play scientist.

Judging by the color of your old coolant, it might not be antifreeze at all but DD powercool additive. In Mass I would use antifreeze.

As for the generator DO NOT use pvc pipe. In your application I would use wet marine exhaust hose with wire from the muffler to the transom or a combination of that and fiberglass pipe made for exhaust which you can buy at marine stores if you can support it properly. But still prefer the wet exhaust hose with wire from point A to B in most situations and yours would be one of them.

I can't remember exactly. I think 10-12 gallons. So half the Powercool and half distilled water.

91/2 gallons.

Going from memory, but I seem to recall 7-8 gallons per engine on my J&T 6-71 TI's.
I used the DD recommended mix at the time, also from memory, 40% antifreeze, 60% distilled water with the power cool additive. Changed it out every two years.
If you don't have to worry about freezing, straight distilled water with the coolant additive.
My boat ran at 165 running and dropped to about 140 once we hit the river and did the slow bell around the island where I docked.

My buddy had 450hp versions of the J&T 6-71 and always had cooling issues. One of the things J&T had him do was run straight distilled water instead of the antifreeze mix.

Gen exhaust - either marine rated exhaust hose or fire retardent marine fiberglass exhaust pipe.

My gen sat in front of the port engine. I ran a short rubber hose up and back to a long piece of fiberglass pipe. Straight run, sloped down and terminated to a fiber glass "saddle" fitting that I epoxied to the top of the port fiberglass exhaust pipe.

In this picture it is the light brown pipe on the right. It was also translucent, so I could see the water flowing through the pipe.

My 6-92's take just about 12 gallons if you drain every pet cock. I use power cool 2000 and distilled water, no antifreeze for me. Attached is some official stuff on coolants for your engine.
My 91 used fiberglass pipe from the muffler out. Never had any problems except the hangers were not stainless.
Dave

It is 9.5 gallons. Direct from my J&T spec sheet.

I bet it depends on which style of heat exchanger you have.

If you're sure on the capacity and the coolant is 50/50 mix, after flushing the old stuff out and draining it. I add (say it takes 9.5 gallons) 4.75 gallons of coolant and then top off with as much water as it takes to top it off etc.

No you can't.
Automotive type antifreeze coolants are specifically excluded from the 2 strokes because they do not offer liner protection, and in fact can lead to water pump & liner (non 2S) pitting.
Modern automotive coolants are designed for aluminum components. There is no aluminum in a 2 stroke that comes in contact with coolant.

6-71 coolant capacity, block, head, t-stat housing and oil cooler = 5.5 gallons.
Your heat exchanger will add whatever additional gallons to the total.
My 410HP TI's were about 7.5 gallons each

I do agree with pulling and throwing away the factory type petcocks. Even if they did drain satisfactorily sooner or later the handle will break off.
Use either solid brass plug or all brass-bronze petcocks.
Completely removing the petcock allows any crud they may be built up behind to drain.
You will have at the minimum, drains on the water pump, outlet elbow, heat exchanger and oil cooler. You may also have a drain on the blower side towards the rear.

This type allows complete removal of the actual stopper.



On the closed cooling system (antifreeze side) solid plugs work because you will infrequently be draining the system.
On the raw water side, a petcock in the 1/4" pipe areas and solid plugs on the 1/8" holes

Adding the mix, I always used a small barrel, added all my distilled water and antifreeze plus the appropriate amount of Powercool and dropped a sump pump in the barrel for a few minutes.
My preference was to added a properly mixed coolant as opposed to adding water and antifreeze separately.

If you maintain the coolant properly and replace it at recommended intervals, you should never see any crud drain.
Detroit recommended interval for marine 2 strokes is 2 years or 4,000 hours.

Correct!
Wet liner engines, the 53 and 92 series do need special coolant. The 71s are dry liners and a good quality antifreeze or an additive such as Penncool if you are going with water only. The 9.5 gallons I stated is for stock cast iron J&T heat exchangers. IMPORTANT: If that did have Dexcool in it, be sure to flush it thoroughly!!!

YES use DETROIT DIESEL (brand) POWERCOOL COOLANT IN YOUR DETROIT DIESEL, it isn't anymore expensive than any of the other stuff. There are DD dealers all over the country. And, there is no question of whether or not it is the right stuff for your engine.

I had already started making some changes before you put this up and apparently once posted for awhile can't be edited. Either way, the non standard automotive type antifreeze, which is high in phosphates and silicates and is not suitable for the DDs of that era or the latest high tech engines. Water pumps on all, wet liners in those with can also be damages by pitting/cavitation.

And to the OP, if you don't know what is in your engine now, drain, flush and put in new. Don't mix old and new.

Not sure what this means.
But from the 2001 coolant guide:
COOLANTS NOT RECOMMENDED The following describes the types of coolants not recommended for use in Detroit engines:
■ All antifreezes and coolants containing phosphorous should be avoided. Drop-out, overheating, and water pump seal failures can result from use of coolant or inhibitor packages based on phosphate.
■ Automotive type coolants generally contain high levels of phosphate and silicate, offer no liner pitting protection, and are not suitable for use in Detroit engines.
■ Methyl alcohol-based antifreeze must not be used in Detroit engines because of its effect on the non-metallic components of the cooling system and its low boiling point.
■ Methoxy propanol-based antifreeze must not be used in Detroit engines because it is not compatible with fluoroelastomer seals found in the cooling system.
■ Glycol-based coolants formulated for heating/ventilation/air conditioning (HVAC) should not be used in Detroit engines. These coolants generally contain high levels of phosphates, which will form deposits on hot internal engine surfaces, reduce heat transfer, and cause water pump seal leaks.


And from the 2017 version:
4.2 Coolants NOT Permitted The following coolants are not to be used in Detroit™ engines:
• Automotive/Passenger car-type coolants must not be used in Detroit™ engines because they offer no liner pitting protection. Also, these types of coolants generally contain high levels of phosphates and silicates.
• Methyl alcohol-based antifreeze must not be used in Detroit™ engines because of its effects on the nonmetallic components of the cooling system and its low boiling point.
• Methoxy propanol-based antifreeze must not be used in Detroit™ engines because it is not compatible with fluorocarbon elastomer seals found in the cooling system.
• Glycol-based coolants formulated for Heating/Ventilation/Air Conditioning (HVAC) must not be used in Detroit™ engines. These coolants generally contain high levels of phosphates, which will form deposits on hot internal engine surfaces, reduce heat transfer, and cause water pump seal leaks.
• Waterless-type coolants must not be used.
• Nitrite Organic Acid Technology (NOAT)must not be used in Detroit™ engines because with poor maintenance components become more vulnerable.