After Cooler Maintenance: Cummins QSB 5.9

I am posting to share the importance of doing the above maintenance whether you have a Cummins or other turbo engine with an after cooler. I had planned to do this at 1000 hours, then came onto Tony Athens' article on "marine age" and realized that my 2006 boat had and after cooler that has had seawater in it, since it was launched!

While I did not find some of the terrible things that neglect can create in this component, I did see the start of seawater intrusion onto the air side of the core and corrosion building up around that o-ring (the bottom, where the seawater sits when engine isn't running).

I always noticed that the lower zinc got eaten up much quicker than any of my other engine zincs (upper after cooler and heat exchanger) and this is likely due to the fact that water sits in that pool always. So...check this zinc every 2-3 months and replace more often as needed.

My after pictures are exactly as shown in Tony's excellent video on how to clean (brake fluid on the air part, simple green on the water side after clearing tubes with a rod, then soak entire core in bucket of simple green to loosen up anything else, rinse, dry, done).

links to my research prior to this job, which I will now do every 2-3 years;

use the recommended grease...
https://www.sbmar.com/articles/cummins-marine-aftercooler-maintenance/

check which o-ring size to use on the QSB
https://www.sbmar.com/articles/b-series-aftercooler-o-ring-identification/

I believe Tony called out a lack of lube on the O Ring at the factory assembly for the AC which allowed the salt water to bridge across as a primary reason, but I haven’t read the article in a few years so correct me if wrong. 13 years is a long time to wait. 3 to 5 years is a better interval.

Following TA’s recipe, I did mine about a year after buying current boat. Getting exchanger out of housing was a chore. It was not plugged up, nice clean tubes, but stuck in housing. After service following SBAR, procedures it has run 3 seasons. Disassembled for service recently, all good again and exchanger, slid easily from housing. If access is good, it is a pretty easy chore.

you are exactly correct. I've only have this boat 1 year, so trying to "catch up" on all that should have been done by previous owner...

pattormey said:

My after pictures are exactly as shown in Tony's excellent video on how to clean (brake fluid on the air part, simple green on the water side after clearing tubes with a rod, then soak entire core in bucket of simple green to loosen up anything else, rinse, dry, done).

Click to expand...

I did see his site some time ago- now I didn't go back to the video, so correct me if I'm wrong here, but I believe that he's using brake cleaner and not brake fluid for cleaning the soot from the air side of the cooler.




This stuff should be in every boat fixer's inventory.

You are correct. I will edit my original post.

I just did mine, be aware that there are two different size O-rings that may be used in that aftercooler. You can put the big one in where the small one belongs and get it back together (the PO of mine did) but the results aren't good. Somewhere around 2006 they changed over from the large to the small. You cannot depend on quickserve.cummins and your serial number or the parts counter for this - mine were clearly called out by serial number as the wrong ones. If you look deep enough there is a Cummins tech note explaining this.

Also, Cummins gets $45 for a standard dash 250 O ring, about one or two dollars anywhere else.

O Ring Size

DDW said:

I just did mine, be aware that there are two different size O-rings that may be used in that aftercooler. You can put the big one in where the small one belongs and get it back together (the PO of mine did) but the results aren't good. Somewhere around 2006 they changed over from the large to the small. You cannot depend on quickserve.cummins and your serial number or the parts counter for this - mine were clearly called out by serial number as the wrong ones. If you look deep enough there is a Cummins tech note explaining this.

Also, Cummins gets $45 for a standard dash 250 O ring, about one or two dollars anywhere else.

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Not to worry, as Tony Athens provides the photos and the explanations in my links above.

I did the service on a pair of QSC engines, so probably similar.


I think the point of the grease is to make disassembly easier the next time you service them. If the coolers have not been greased and not been apart for a long time, getting them apart can be a problem.

Look what I found on a 250 hour QSB. And the boat was serviced by highly regarded boat yard.

DDW said:

I just did mine, be aware that there are two different size O-rings that may be used in that aftercooler. You can put the big one in where the small one belongs and get it back together (the PO of mine did) but the results aren't good. Somewhere around 2006 they changed over from the large to the small. You cannot depend on quickserve.cummins and your serial number or the parts counter for this - mine were clearly called out by serial number as the wrong ones. If you look deep enough there is a Cummins tech note explaining this.

Also, Cummins gets $45 for a standard dash 250 O ring, about one or two dollars anywhere else.

Click to expand...

Just got a boat with 2xQSB380 and I'm taking aftercoolers apart. I found only 2 fat o-rings sealing core one on the top and one on the bottom. Both of them look the same. Just got a quote from Harbor Marine in Seattle for 2 gasket sets for aftercoolers and 2 sets for heat exchangers 730$ is that insane or what ? I can't believe it. Are these magic o-rings ? I have a feeling they are standard silicone o-rings which cost 99c for all truck drivers but sold to suckers like me for insane profit. I'm thinking ordering these o-rings, measuring thickness and diameter and returning them just to buy generic silicone o-ring online. Please tell me if I'm missing something here ?

Also, there are bunch of connecting 4 inch long hoses, cummins wants 75$ a pop for. Are they standard 4ply silicone hoses I can buy online for 40$ a yard for . I've seen a lot of them produced for car turbo applications

Romanp said:

Just got a boat with 2xQSB380 and I'm taking aftercoolers apart. I found only 2 fat o-rings sealing core one on the top and one on the bottom. Both of them look the same. Just got a quote from Harbor Marine in Seattle for 2 gasket sets for aftercoolers and 2 sets for heat exchangers 730$ is that insane or what ? I can't believe it. Are these magic o-rings ? I have a feeling they are standard silicone o-rings which cost 99c for all truck drivers but sold to suckers like me for insane profit. I'm thinking ordering these o-rings, measuring thickness and diameter and returning them just to buy generic silicone o-ring online. Please tell me if I'm missing something here ?

Also, there are bunch of connecting 4 inch long hoses, cummins wants 75$ a pop for. Are they standard 4ply silicone hoses I can buy online for 40$ a yard for . I've seen a lot of them produced for car turbo applications

Click to expand...

Goto SBMAR.com

Romanp said:

Just got a boat with 2xQSB380 and I'm taking aftercoolers apart. I found only 2 fat o-rings sealing core one on the top and one on the bottom. Both of them look the same. Just got a quote from Harbor Marine in Seattle for 2 gasket sets for aftercoolers and 2 sets for heat exchangers 730$ is that insane or what ? I can't believe it. Are these magic o-rings ? I have a feeling they are standard silicone o-rings which cost 99c for all truck drivers but sold to suckers like me for insane profit. I'm thinking ordering these o-rings, measuring thickness and diameter and returning them just to buy generic silicone o-ring online. Please tell me if I'm missing something here ?

Also, there are bunch of connecting 4 inch long hoses, cummins wants 75$ a pop for. Are they standard 4ply silicone hoses I can buy online for 40$ a yard for . I've seen a lot of them produced for car turbo applications

Click to expand...

Give Seaboard Marine a try. Here's their service kit for AC and HX. Spend some time on their site and get to know your engines. They are absolutely a treasure trove of Cummins Marine information.

Romanp said:

Just got a boat with 2xQSB380 and I'm taking aftercoolers apart. I found only 2 fat o-rings sealing core one on the top and one on the bottom. Both of them look the same. Just got a quote from Harbor Marine in Seattle for 2 gasket sets for aftercoolers and 2 sets for heat exchangers 730$ is that insane or what ? I can't believe it. Are these magic o-rings ? I have a feeling they are standard silicone o-rings which cost 99c for all truck drivers but sold to suckers like me for insane profit. I'm thinking ordering these o-rings, measuring thickness and diameter and returning them just to buy generic silicone o-ring online. Please tell me if I'm missing something here ?

Also, there are bunch of connecting 4 inch long hoses, cummins wants 75$ a pop for. Are they standard 4ply silicone hoses I can buy online for 40$ a yard for . I've seen a lot of them produced for car turbo applications

Click to expand...

Welcome to boating .

The O-rings are standard size. In fact a dash 353, like this one from McMaster, $6.68 for two. (Of course, this is the internet so verify for yourself). I'd give you 4 new ones if I could only get to my boat, as I bought the large ones and needed the small ones, so in a rush went down and paid $40/ea for them at Cummins. I believe the Cummins seal kit comes with the silicone side seals, which seem to have no reason and SBMar says leave them out. SBMar is much more reasonable than Cummins, they only want $45 for the $7 O-rings.

DDW said:

Welcome to boating .

The O-rings are standard size. In fact a dash 353, like this one from McMaster, $6.68 for two. (Of course, this is the internet so verify for yourself). I'd give you 4 new ones if I could only get to my boat, as I bought the large ones and needed the small ones, so in a rush went down and paid $40/ea for them at Cummins. I believe the Cummins seal kit comes with the silicone side seals, which seem to have no reason and SBMar says leave them out. SBMar is much more reasonable than Cummins, they only want $45 for the $7 O-rings.

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Thank you for the recommendation. Any thoughts on connecting hoses?

They are 70 durometer o rings. $2.00 each

Seaboard marine www.sbmar.com sells the kits as well as individual hoses.

Romanp said:

Thank you for the recommendation. Any thoughts on connecting hoses?

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The only hose I'd buy from Cummins would be the ones that must be molded into a particular odd shape. Anything else I'd get a high quality hose that said Gates on it. That is very likey the source for Cummins.

DDW said:

The only hose I'd buy from Cummins would be the ones that must be molded into a particular odd shape. Anything else I'd get a high quality hose that said Gates on it. That is very likely the source for Cummins.

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You can find automotive hoses to cut out the section with the bend you want. My old T6 Perkins acquired at least one hose which was intended for a Ford Fairlane.

After cooler/intercooler or heat exchanger?
Looks like heat exchanger.

The pic in post 10 is the bottom view of a QSB aftercooler. Still technically a heat exchanger.