Good afternoon everyone,

Could someone who has done the aftercooler service on their NT37 Cummins
let me know what I ought to know before addressing the service myself? (How
much time it is likely to take, what special tools I need, what service kit
I should look at, tips and tricks, etc.)

Thanks,

-Jonathan

Cyclops
NT37-138
Freeport, Maine

Jonathon,

I have done that service several times on our NT37. Since our hull number is 136 I expect the procedure is identical.

Time is difficult to estimate, since experience level counts, and any problems can extend the time indefinitely.

I would estimate under an hour to remove everything. Disassembly can take 10 minutes or a long time, depending on how "stuck" the core is. If your aftercooler has never been serviced, it could be a challenge to get it apart.

Cleaning can take an hour or more, depending on what you need. Make sure you do not soak the entire core in dilute HCl, because the outside fins are aluminum on this vintage cooler. If you cap one end with a large rubber drainage pipe cover and stand the core on end you can fill the tubes with acid. You can also use a rod to clean the tubes.

The biggest concern is corrosion of the aluminum housing. It is quite likely that you will find some level of corrosion. If it is on a sealing surface it will need to be dealt with. This includes the outer faces (where the o-rings go) as well as the bore that contains the ends of the core. It is possible to remove a small amount from the faces with careful filing or sanding. Be sure that you do not make to housing too short to fit the core, including slack for possible thermal expansion.

If everything looks OK (or is made OK) then you can assemble and test. The pros advise that you test the core first, then assemble and test the entire aftercooler. I choose to assemble first and then test everything at once. The downside is that if there is a leak it will be necessary to disassemble and test the core separately. This takes time (and money) for a professional, but I have plenty of time. The upside is that only one test rig (for the entire assembly) needs to be goobered together. (technical term!)

Make sure you carefully select the correct o-rings when assembling (I need the large ones) and use lots of Metalube grease everywhere metal touches metal.

Reinstallation takes a bit more time than removal, but still should be no more than an hour or so.

No special tools are required. Ordinary metric wrenches/sockets will do.

I presume you are familiar with Tony's instructions and videos at Seaboard Marine. If not, be sure to look there.

Regards,

Gene Fuller

Yorkshire Rose

Punta Gorda, FL

NT37-136

On 2/2/2026 1:41 PM, Jonathan Handelman via Sentoa wrote:

Good afternoon everyone,

Could someone who has done the aftercooler service on their NT37 Cummins let me know what I ought to know before addressing the service myself? (How much time it is likely to take, what special tools I need, what service kit I should look at, tips and tricks, etc.)

Thanks,

-Jonathan

Cyclops

NT37-138

Freeport, Maine

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Jonathan,
Difficulty entirely depends on how long it’s been since it was serviced last. Good owner DIY project if you are mechanically inclined. Messy but entirely doable.
Recommended aftercooler maintenance interval in salt water is 2 years regardless on engine hours.
Takes me a few hours but I’ve been religious on the every 2 yrs.
Nothing special for tools, a good work surface and room to make a mess.
Buckets are important and a place to clean something that will likely be nasty.
Having a vise on heavy bench helps because of the irregular shape.

Sbmar.com is an outstanding resource.  here’s a link to their article on the subject from their Tony’s Tips knowledge base.
https://www.sbmar.com/articles/cummins-marine-aftercooler-maintenance/
[aftercooler-assembly-3.jpg]
Cummins Marine Aftercooler Maintenancehttps://www.sbmar.com/articles/cummins-marine-aftercooler-maintenance/
sbmar.comhttps://www.sbmar.com/articles/cummins-marine-aftercooler-maintenance/

My 2 cents:

This sucker is heavier than you think.

Try to work on it horizontally if you can.

Do not unbolt both bronze end caps until you are prepared to attempt to slide the core.

The bronze tube bundle core is fragile and very expensive, if it was serviced properly last time, will slide right onto the floor!

There are tricks if your core doesn’t slide out easily, email me if you get frustrated.

Never re-use the old o-rings!

Be advised different model years use different o-rings and it’s not obvious looking at the deformed old ones whether yours needs the thick ones or the thin ones - use sbmar.com resources to tell the difference and which ones to buy (Cummins once sold me the wrong ones for my engine no.)

I use a local radiator shop that will pressure test my aftercooler once I’ve serviced and re- assembled it. Good peace of mind to keep salt water out of the engine.

Good luck.
Kelly Britz
SANDPIPER, NT37-042, Seattle/Edmonds

Sent from my iPhone

On Feb 2, 2026, at 10:42 AM, Jonathan Handelman via Sentoa sentoa@lists.sentoa.org wrote:


Good afternoon everyone,

Could someone who has done the aftercooler service on their NT37 Cummins let me know what I ought to know before addressing the service myself? (How much time it is likely to take, what special tools I need, what service kit I should look at, tips and tricks, etc.)

Thanks,

-Jonathan

Cyclops
NT37-138
Freeport, Maine

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