Onan MDKBM maintenance - coolant, thermostat, v-belt tension

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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!
 
With respect, didn't you get a manual?
 
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.
 
Xsbank said:
With respect, didn't you get a manual?
Click to expand...

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.
 
Alaskan Sea-Duction said:
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.
Click to expand...

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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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.
 
tadhana said:
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.
Click to expand...

100%
 
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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Thermostat was easy. Used Permatex Ultra Grey instead of Three Bond 1215
 
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.
 
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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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.
 
tadhana said:
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.
Click to expand...

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.
 
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.
 
tadhana said:
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.
Click to expand...

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!
 
for v belt tension, get a Gates 91107 Belt Tension Tester for about $12
 
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?
 
tadhana said:
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?
Click to expand...

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!
 
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!
 
tadhana said:
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!
Click to expand...

Ok thanks. Was thinking gasket maker but sounds like that is overkill.
 
If coolant is still clear as most are, just a drain and flush and refill is all that is needed. No need to chemically clean the coolant side as it is hard to get all the chemical out.

Why replace the thermostat? I have found Kubota tstats to be very reliable.

Heat exchanger should be chemically cleaned on the sea water side say every five or so years. Remove it to clean. If it has the central bolt end caps, it is probably a SenDure unit and the cap gaskets are generic. Replace them and end caps, available almost any marine supply house. Not sure about putting silicone grease on them as that may become a persistent lubricant and allow the gasket to extrude. Clean and dry is fine. And end of HX must be clean clean clean.

Belt tension, just put it "snug". Hard to describe, but it does not have much load on it driving alt and circ pump, so just snug it down so it does not flop around when running.
 
Ski in NC said:
Why replace the thermostat? I have found Kubota tstats to be very reliable.
Click to expand...


True, It is always best practice to check the thermostat as they get rust on them that affects their operation. Cheap insurance.
 
Out of curiosity, does anyone know if the ODKBM has an alternator? I.e. will it charge the genset starting battery while running or do I need to use a battery charger?
 
Look at what the belt drives. Bottom pulley is crank. Up top is circ water pump and off to one side is alternator, of some sort. I think your unit has a std car alternator. Some have permanent magnet alternator and a motorcycle type regulator (shunt type). PM types look like a bell, car alt types you can see the windings through air vents in the case.
 
Quick question

Volvo filter # 3581078 comes with three large gaskets (I think two same size, one larger) and two small

Two small I have figured out

One larger goes on bottom of fuel filter between the bowl and filter as indicated by red arrow

Other larger goes up in lip of metal assembly as shown by a red arrow

But where does the third larger one go? In the lip of the fuel filter as shown by the yellow arrow??? If so, aren't there essentially two gaskets there then? (one in the metal lip and one at the top of the fuel filter)

Thanks
 

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All

I know I raised this a year ago but I am thinking about Barnacle Buster flush on the raw water side of the Onan MDKBM

Curious if the genset can be flooded by forcing water through the raw water side? I have heard many flood their gensets and destroy them. I think it was in relation to a high speed water pickup or something letting water in when the generator was not running. Just want to make sure if I attempt this I am not going to break anything...

Thanks!
 
Does the smaller (water) hose come easily off the exhaust mixer? If so you can use that as one of the recycle points. With that off the mixer, no was to get the fluid to back up into engine. Just don't start it with it off.

Also when done and all back together, run it for many hours to get as much of that solution flushed out.
 
Mystery -
What makes you think you need a BB treatment?
I freshwater flush about 1 x per month and add salt away.
So far no issues (5 years old)
 
hi does anyone know if the MDKBM is considered fresh water cooled? can water get into the generator and cause damage if i leave the seacock valve open when underway but not running the generator?
 
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