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Old 06-04-2018, 09:15 AM   #1
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Onan MDKBM maintenance - coolant, thermostat, v-belt tension

Hello all,

I am embarking to change the coolant and thermostat on my Cummins Onan MDKBM generator. I have procured the parts (pressure cap, thermostat) and supplies (coolant and Cummins Fleetguard Restore coolant system cleaner).

Any tips or tricks to flushing the cooling system and replacing the coolant? Do I simply drain the existing coolant, refill with restore in the coolant resevoir, start engine, refill to get to the right level, let sit for a few hours, drain, replace with coolant and new pressure cap?

Any tips or tricks for replacing the thermostat?

Any tips or tricks for checking the v-belt tension? Do most carry a spare belt?

I may also do the impeller soon so open to tips and tricks for that too (it hasn't been a year yet and not close to 500 hours).

Thank you!
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Old 06-04-2018, 12:37 PM   #2
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With respect, didn't you get a manual?
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Old 06-04-2018, 12:58 PM   #3
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You should be able to access a drain plug on the block to drain the coolant. Once you drain it, fill it with water and add a radiator cleaner, the fill and drain a few times. Then add new coolant. Replacing the thermostat is straight forward. Just don't over torgue the bolts.
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Old 06-04-2018, 02:00 PM   #4
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With respect, didn't you get a manual?
I have the operators manual. It has instructions for most of the items but not cleaning/flushing the cooling system... it says:

"Follow the manufacturer's instructions for cleaning and flushing"

"Use radiator cleaning chemicals to clean and flush the cooling system before refilling with fresh coolant. Follow the cleaner manufacturer's instructions"

I was also looking for tips and tricks from folks that have done this before. Some times there is good advice that can prevent an issue or mess.
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Old 06-04-2018, 02:02 PM   #5
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You should be able to access a drain plug on the block to drain the coolant. Once you drain it, fill it with water and add a radiator cleaner, the fill and drain a few times. Then add new coolant. Replacing the thermostat is straight forward. Just don't over torgue the bolts.
Thanks but how do I circulate the cleaner through the system? Do I need to start the engine? I did note the manual has warnings about adding cold water to the cooling system but should I use room temperature water or hot water? Why would I fill it with water and then add radiator cleaner? Or did you mean use water to flush out the cleaner? Should I use distilled water? I am assuming the radiator cleaner is only going through the closed part of the cooling system and the raw water side would be flushed separately using something like barnacle buster?
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Old 06-04-2018, 02:44 PM   #6
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I have the MDKBH. Have done mine twice now in 9 years, 900 hours. Getting to the drain plug is really tough. it is sort of tucked under the generator end. I drained the coolant ad added the Cummins cleaner. Ran it for about 20 minutes. Drained it. Added distilled water and ran it about half an hour. Drained it. Then added the coolant. Each time I ran it there would be air bubbles so I would stop and top it off about every 5 minutes until it was holding volume. If you can find out if it is the same manual, I might have a PDF of it some where.
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Old 06-04-2018, 03:35 PM   #7
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i have the mdkbh. Have done mine twice now in 9 years, 900 hours. Getting to the drain plug is really tough. It is sort of tucked under the generator end. I drained the coolant ad added the cummins cleaner. Ran it for about 20 minutes. Drained it. Added distilled water and ran it about half an hour. Drained it. Then added the coolant. Each time i ran it there would be air bubbles so i would stop and top it off about every 5 minutes until it was holding volume. If you can find out if it is the same manual, i might have a pdf of it some where.
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Old 08-23-2018, 03:41 PM   #8
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So coolant flush and replacement not bad. Had to remove battery box, battery, and side of generator to get access to the coolant drain though. About to do thermostat.

Also doing oil change. How much oil are you guys getting out through the oil drain hose? Is the capacity measured at the full tick on the dipstick? Oil capacity says it is about 1.15 gallons but I've only been able to pull about .7 gallons out...but the dip stick was at 1/3 and the oil filter was full.
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Old 08-25-2018, 10:55 AM   #9
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Thermostat was easy. Used Permatex Ultra Grey instead of Three Bond 1215
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Old 08-25-2018, 12:06 PM   #10
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With respect to coolants please review what is meant by ASTM D3306, ASTM D4895, ASTM 6210, and what is an OAT coolant? Some coolants can damage some engines.


I like the stuff that is easiest to get in case I want more later. Shops and parts stores will usually take old coolant for recycling.
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Old 01-15-2019, 01:17 PM   #11
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Hello all,

I am planning to use barnacle buster to clean out the raw water side of my Onan MDKBM in the next couple months. I can pull off the raw water inlet hose from the seacock and connect that to a pump to circulate but wondering where I should connect the outlet on the MDKBM to reclaim into a bucket for circulation?

I plan to let it circulate through for 2-4 hours. I will remove the impeller and zinc anode (or just leave the anode and replace it after). Anything else I should remove or be aware of? Is the thermostat fine to leave in?

Attached is a pic.

Thanks!
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Old 01-15-2019, 02:24 PM   #12
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Are you cleaning the salt water side or the freshwater side. The thermostat is in the freshwater side. Does yous have an anode? My MDKBH does not. If cleaning the salt water side, put the cleaning solution in a bucket with a small 12v bilge pump. Connect he pump discharge hose to the heat exchanger where the saltwater goes in. run a second hose from the mixing elbow back to the bucket. Connect the bilge pump to 12v and let it run, After a while reverse the hoses so you revers the flow in the salt water side of the system.
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Old 01-15-2019, 03:28 PM   #13
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Originally Posted by tadhana View Post
Are you cleaning the salt water side or the freshwater side. The thermostat is in the freshwater side. Does yous have an anode? My MDKBH does not. If cleaning the salt water side, put the cleaning solution in a bucket with a small 12v bilge pump. Connect he pump discharge hose to the heat exchanger where the saltwater goes in. run a second hose from the mixing elbow back to the bucket. Connect the bilge pump to 12v and let it run, After a while reverse the hoses so you revers the flow in the salt water side of the system.
Excellent catch. I am talking about raw water. Now I remember the thermostat is on the freshwater side because I drained, flushed, replaced thermostat, pressure cap, and coolant a few months ago. My bad.

Any chance you can please mark the picture I uploaded with where I should connect on the heat exchanger and mixing elbow? You are suggesting avoiding the raw water pump altogether?

Thanks.
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Old 01-15-2019, 04:16 PM   #14
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Usually there is no need to flush the pump. My genset is 5 KW 2 cylinder, so not exactly like yours. Can't see the exhaust or the heat exchanger in your picture. Trace the hose on the discharge side of the pump. That's the one not leading to the sea cock! What ever that connects to, probably, the heat exchanger around on the other side of the generator is one point of connection. Next find where the exhaust hose connects to the engine at the mixing elbow. The water line (not the exhaust hose) line into the mixing elbow is the other point of connection.


The set looks nice and clean. How old is it? How many hours? Do you need to clean the raw water side at all? I have 950 hours. . I pull the end off the heat exchange every 200 hours or so and look. It has always been clean, unlike the engine heat exchanger which needs to be cleaned about every 1000-15000 hours in salt water operation. On the other hand, the fresh water side is harder to check I clean and flush it every 2-3 years when I do the main engine.
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Old 01-15-2019, 04:37 PM   #15
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Usually there is no need to flush the pump. My genset is 5 KW 2 cylinder, so not exactly like yours. Can't see the exhaust or the heat exchanger in your picture. Trace the hose on the discharge side of the pump. That's the one not leading to the sea cock! What ever that connects to, probably, the heat exchanger around on the other side of the generator is one point of connection. Next find where the exhaust hose connects to the engine at the mixing elbow. The water line (not the exhaust hose) line into the mixing elbow is the other point of connection.


The set looks nice and clean. How old is it? How many hours? Do you need to clean the raw water side at all? I have 950 hours. . I pull the end off the heat exchange every 200 hours or so and look. It has always been clean, unlike the engine heat exchanger which needs to be cleaned about every 1000-15000 hours in salt water operation. On the other hand, the fresh water side is harder to check I clean and flush it every 2-3 years when I do the main engine.
OK I will probably have to take the side off any take a better picture. Its very tight space to work in. There is no chance of the engine ingesting barnacle buster because it has coolant and is not raw water cooled, is that correct?

Its only a couple years old. ~400 hours. Put 300 on in the past year. We were aboard for most of the past year. Figured I'd tackle while I have Barnacle buster left over from doing the Volvo engines...

Thanks!
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Old 01-15-2019, 05:25 PM   #16
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for v belt tension, get a Gates 91107 Belt Tension Tester for about $12
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Old 01-15-2019, 05:44 PM   #17
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for v belt tension, get a Gates 91107 Belt Tension Tester for about $12
Thanks!!! Going to grab one!
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Old 01-15-2019, 05:44 PM   #18
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My bet is that there is no need to do the barnacle buster cleaning. Save the stuff it is expensive. . You can use it to clean AC units. See if you can get to the heat exchanger. You should be able to take of an end cap and look inside the raw water side of the heat exchanger . I will bet it is clean and bright. Save that expensive cleaner for use when you really need it somewhere. Are you operating in salt water?
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Old 01-15-2019, 05:54 PM   #19
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My bet is that there is no need to do the barnacle buster cleaning. Save the stuff it is expensive. . You can use it to clean AC units. See if you can get to the heat exchanger. You should be able to take of an end cap and look inside the raw water side of the heat exchanger . I will bet it is clean and bright. Save that expensive cleaner for use when you really need it somewhere. Are you operating in salt water?
Yes I am operating in saltwater

If I open up the heat exchanger, do I need to put a new gasket on and seal? If so, any idea on part # or if there is a kit with everything needed? Thanks!
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Old 01-16-2019, 10:07 AM   #20
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The heat exchanger probably has a rubber gasket seal. Use a little silicone grease (most any grease but not Vaseline..It contains hydrocarbons. Hydrocarbons can soften some rubbers. Silicone grease will not). I've been using silicone grease on my engine and gen set for 10 years, The gaskets are still fine. A small dab of silicone grease on the threads of your deck (fuel) fills and on the threads of your sea strainer caps will also help them seal and reduce the chance that they will get stuck!
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