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Old 04-24-2021, 08:12 PM   #1
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Onan 10HDKCA Overheating

Hey everyone.


So I have a few questions regarding my Onan generator.
The unit is a Onan (Kubota engine) 10HDKCA.

I have had this thing running on and off. Sometimes it will run 4 hrs no issues...other times it will run 15 minutes and throw a 3-6 code.

I've went through and verified the fuel pump is pumping. It has a little shake/vibration to it. Both while priming and running.

I've also looked at fuel flow before and after the diesel filter...it fills up a solo cup in like 15 seconds. It's fresh diesel (no black slime and looked at my coalescing filter in the engine run bay...no water so I feel confident my diesel is good). I also added some diesel additive to the tank when I bought 90 gallons the other day. I also re-bled fuel at the injectors. I'm pretty comfortable around diesels. Pretty simple...air...fuel...compression. BOOM!

I've cleaned the air cleaner element. So that shouldn't be an issue. Plus it's new. Only ~20 hrs on it. Bought it direct from Kubota.

The belt is connected to the main crank and water pump (my model doesn't have a tensioner). It feels loose for my liking (~.5" of deflection if I push) but when the crank spins, it spins the pump. No squeaking. No rubber smell. I've also taken the belt off and spin the pump pulley... It spins.

Fast forward to me diagnosing this mess. I took all the panels off and it ran smooth for ~10 minutes then shut off with a high temperature (one blink) code. This is a fresh surprise considering I've been getting 3-6 codes. So it's welcome...sorta. What it tells me is that my temperature sensor is working!!! So that's freaking awesome to know.

However, I've been reading that these engines need the cowling installed for adequate cooling? Is this a real reason for it to throw a high temperature code? AFTER throwing 3-6 codes about 4 seperate times after runtimes between 30 minutes and 4 hrs.

Back to diagnosing....

I've squeezed the intake and exit coolant hoses...when I squeeze one hose the other pushes back (engine off; coolant cool). Making me think that the radiator isn't clogged, and furthermore the thermostat is open? But could it still be clogged? Enough to throw a temp code. Keep in mind I had been getting 3-6 codes for a random engine stall/quit and this is my first time getting a temp code; allbeit with the cowling off.

I've also sqeazed the hoses when the engine is running (cowl off) and the hoses are hard (both sides) making me think the water pump is pushing coolant but the radiator is causing a restriction?

Do any of y'all think it could be the thermostat? Maybe my squeezing was a result of the coolant moving through the bypass hoses...?

Can I (potentially) remove the thermostat and run it to see if it still overheats? At least be safe enough to get my stuff charged to get on the road?

Any help would be great. Honestly I'm in the weeds here...I've done so much to diagnose.. also we do have an AutoGen Start system and it's disabled right now...so that shouldn't be messing with anything related to the genny.

Right now I'm at Talladega running the bus engine to recharge every 5 or 6 hrs at a time.

My plan (after I limp home) is to start tearing this down to the radiator.. looking for abrasions on hoses, etc.

Replacing: water pump belt, thermostat, water pump, and cleaning the radiator with something?

Again, any help is appreciated.
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Old 04-24-2021, 08:31 PM   #2
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Have you contacted Kubota sales yet? I would expect them to be helpful for a genset with 20 hrs on the meter.
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Old 04-24-2021, 08:52 PM   #3
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Have you contacted Kubota sales yet? I would expect them to be helpful for a genset with 20 hrs on the meter.
No...the generator has 2k hours. The air filter has 20 hrs..
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Old 04-24-2021, 11:13 PM   #4
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No...the generator has 2k hours. The air filter has 20 hrs..
My bad, speed reading got me again.
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Old 04-25-2021, 04:40 PM   #5
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When is the last time you've changed the coolant system roketenginer? These units need the coolant changed out every 3 years to keep them in tiptop running shape..I learned this the hard way & it was very expensive to have Cummins do something I'm capable of doing. I just did mine yesterday with a flushout too.
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Old 04-25-2021, 08:47 PM   #6
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Thermostat first, your time to overheat is all over the place. If that's due to load on the gen being different then I would lean towards a bad radiator. A radiator can be clean and still be deteriorated to the point it won't cool. The overheating is gradual and may not overheat while under a light load.
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Old 04-25-2021, 10:11 PM   #7
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When is the last time you've changed the coolant system roketenginer? These units need the coolant changed out every 3 years to keep them in tiptop running shape..I learned this the hard way & it was very expensive to have Cummins do something I'm capable of doing. I just did mine yesterday with a flushout too.
I haven't. Just oil, oil filer, fuel filter, air cleaner. I'll be doing a flush and replacing the thermostat, inspecting the lines for holes (sucking in air maybe), and boiling the radiator to clean it out.

I checked the airflow with the cowling on. It sucks air up from the bottom at the radiator. So the fan is developing a vacuum and moving air through the cowling.
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Old 04-26-2021, 01:00 AM   #8
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If pump working, not leaking thru weep hole, fluid level good/ full and fan/ fan clutch (if equipped) good, most likely THERMOSTAT; they can go bad suddenly, either stick shut, stick up, even had one snap in half suddenly
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Old 04-26-2021, 11:11 AM   #9
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Copy, I'm gonna plan on doing a full coolant flush of the coolant as well as thermostat replacement and inspection of the water pump. The RV is a 07 Monaco Dynasty 43' tag axle and the mx records are a little lacking from the previous owner. I'm an airline pilot so records of mx are essential where I'm from.

Question, do you know of anyone putting a coolant temp gauge on the generator? Like with an actual AutoMeter gauge? I'd rather know the problem could be developing rather than be surprised. I do a lot of RVing over-the-road w/ the generator on (at least with my former Bounder I did) and I'd like to know the condition of the generator going down the road if at all possible from the driver's seat. And maybe an oil PSI/temp gauge as well? I looked on the generator and there are a few sensor bungs that have wires leading off it I could steal those signals for some gauges? There's no such thing as too much data!
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Old 04-26-2021, 07:17 PM   #10
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Genie coolant change out

There's a great video on YouTube on hoe to change out & flush your genie







Quote:
Originally Posted by roketenginer View Post
I haven't. Just oil, oil filer, fuel filter, air cleaner. I'll be doing a flush and replacing the thermostat, inspecting the lines for holes (sucking in air maybe), and boiling the radiator to clean it out.

I checked the airflow with the cowling on. It sucks air up from the bottom at the radiator. So the fan is developing a vacuum and moving air through the cowling.
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Old 04-26-2021, 07:34 PM   #11
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Before getting too crazy with coolant system (although it sounds like service is due) I would want to know the temp switch is not failing. It's a cheap easy to replace part or I'm sure you can look up how to ohm test it. If it's sending faulty signals it could be shutting it down. I also would love a temp gauge on the genny. I'm sure there is a way to wire one in.
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Old 04-27-2021, 03:29 PM   #12
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I checked the sensor it showed 1 ohm cold.

Is there a way to 'test' a radiator? Can I blow low psi compressed air through it? Or should I just leave it be and use prestone cleaner to get the scaling out?
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Old 04-27-2021, 05:50 PM   #13
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I ordered a pressure fill cap, temperature sensor, and thermostat. I will refill with some quality fluid after.

I tested flow of the radiator, it flows very well. If I still get overheating issues I will know THAT is where my problem is.
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Old 04-28-2021, 06:54 AM   #14
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Quote:
Originally Posted by roketenginer View Post
I ordered a pressure fill cap, temperature sensor, and thermostat. I will refill with some quality fluid after.

I tested flow of the radiator, it flows very well. If I still get overheating issues I will know THAT is where my problem is.

You could also pick up one of those cheap thermometer laser guns. You could know actual temp of coolant in different parts of the system as it runs. Would prob be able to tell if there is a blockage in the the radiator and for sure see if the thermostat is stuck closed.

Amazon Thermometer Gun
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