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Onan Generator 7500 Quiet Diesel

DANO2014
Explorer
Explorer
Having problems with my generator, Onan 7500....runs OK until I turn my A/C on. When it loads up the generator will run about 5-10 minutes and kill.
I am getting three blinking lights on the switch after stopping. According the manual it mentions abnormal maintanence problems. I will bring it to a Onan dealer in the morning but was checking on any suggestions available information from those that may have experience these issues.
DANO2014
Allegro Bus 2002
Retired: Cameron Iron Wks
U.S. Army Veteran
Louisiana Masons
11 REPLIES 11

DANO2014
Explorer
Explorer
I believe my generator problem may be solved!!
Brought it in to repair facility this morning and as he
was checking the Fault Code again he notice an
inline fuel filter behind the generator. Disconnected
hose on both ends & emptied into a pan where
he saw a lot of trash, attempted to blow into
hose which was restricted. He blew into it
with a air hose & more goop/trash came out
but still restricted. Hose were cracked on both
sides no doubt allowing air causing cavitation.
Changed out with new hose direct & did not install
Another filter since most do not have?
Why mine I could not tell you.... I hope this
Is my problem which no doubt believe it to be.
Thanks for your help
DANO2014
Allegro Bus 2002
Retired: Cameron Iron Wks
U.S. Army Veteran
Louisiana Masons

FIRE_UP
Explorer
Explorer
DANO2014 wrote:
OK, brought coach to have my generator checked out for previous stated problems. Technician found the Fault Code No 36 and checked out unit. Could not find any problems so I instructed him to change Oil & Filter, change out fuel filter and air filter plus anything else that he thought necessary to eliminate issues.
Tech ran it for 2 1/2 hours with a full load, no problems and I ran it for another 2 hours, no problems.
Left for a day trip about 220 mile r/t. Generator worked great on the way down. Parked coach left generator running with full load and was gone maybe 3 hours. Came back to coach, generator had stopped running..checked oil level-OK, Fault Code again was 36. Restarted unit but was a little sluggish and I had to hold down on my start button until it started. I normally don't have to do that once the glow plugs heat up it cranks with ease. It stopped again on the return trip after parking for about an hour to eat dinner. Came back out and generator had stopped again....cranked again and ease the load by cutting rear A/C off running just the front...ran OK all the way back home which was about 2 1/2 hours, no issues..
I am bringing it back to the repair facility in the morning in hoping they can find the problem....I am beginning to think it could be in the coolant and/or thermostat? Confused by not giving up !
Any suggestions would be greatly appreciated....sorry for the long message.


Well Sir,
As I stated earlier in my previous post, if you were having an "over heat" condition, it would present a code 33. Now, this does not mean you're not having one, it's just that, it's typically going to produce that specific code if, there's any of the conditions exist, that would cause a high heat condition.

While these 7.5 QD units are great little generators, they can throw fits now and then that cause some head scratching. I have corresponded to a few on here and IRV2 that have had that "over heat" condition and, for about 99.99% of them, the cause was the infamous temp sensor, located in the lower thermostat housing.

The temp sensor is about the same shape as a spark plug. And, the condition is resides in, is real close proximity. In other words, there's very limited flow of coolant around it. So, being in that kind of environment, it eventually builds up a hard calcium type corrosion all around that sensor and, therefore, sort of "grounds out" which, causes false signals to that little diesel ECM.

It's actually presenting an over heat condition, when in fact, the little diesel is running just fine. But, the ECM can only respond and, act on, what it's told are operating conditions.

Some, like me, had one serious pain in the a$$ time of getting that sensor out due to the corrosion on the threads and sensor tip. But, others, were not so bad off. Theirs came right out.

There was one gent, I think he/they go by the user name of "Joe and Angela" who actually by-passed the sensor, faking out the engine ECM with a new sensor, taped to the radiator hose, emanating from the thermostat. IT WORKED! That little engine kept right on running in the hottest conditions.

So, anyway, you'll have to do a bit more investigating to see if that's your problem and, it's just not throwing the correct code. Good luck.
Scott
Scott and Karla
SDFD RETIRED
2004 Itasca Horizon, 36GD Slate Blue 330 CAT
2011 GMC Sierra 1500 Ext Cab 4x4 Toad
2008 Caliente Red LVL II GL 1800 Goldwing
KI60ND

Preacher_Man
Explorer
Explorer
Check for airflow over the radiator. Depending on how it's been used, you can accumulate a lot of garbage that will block the airflow. Had this happen more than once. It would run ok on a 1 ac, but load it up and it would eventually overheat and shutdown.
Mark Walter
J-Angel Productions
Web and Media Company
2004 Sportscoach LE 376 DS
Cat 3126E, Allison 3000

DANO2014
Explorer
Explorer
OK, brought coach to have my generator checked out for previous stated problems. Technician found the Fault Code No 36 and checked out unit. Could not find any problems so I instructed him to change Oil & Filter, change out fuel filter and air filter plus anything else that he thought necessary to eliminate issues.
Tech ran it for 2 1/2 hours with a full load, no problems and I ran it for another 2 hours, no problems.
Left for a day trip about 220 mile r/t. Generator worked great on the way down. Parked coach left generator running with full load and was gone maybe 3 hours. Came back to coach, generator had stopped running..checked oil level-OK, Fault Code again was 36. Restarted unit but was a little sluggish and I had to hold down on my start button until it started. I normally don't have to do that once the glow plugs heat up it cranks with ease. It stopped again on the return trip after parking for about an hour to eat dinner. Came back out and generator had stopped again....cranked again and ease the load by cutting rear A/C off running just the front...ran OK all the way back home which was about 2 1/2 hours, no issues..
I am bringing it back to the repair facility in the morning in hoping they can find the problem....I am beginning to think it could be in the coolant and/or thermostat? Confused by not giving up !
Any suggestions would be greatly appreciated....sorry for the long message.
DANO2014
Allegro Bus 2002
Retired: Cameron Iron Wks
U.S. Army Veteran
Louisiana Masons

DANO2014
Explorer
Explorer
Not sure I found my problem but brought my coach to check out my Onan 5700 QD to a repair facility. My code on generator was 36 meaning I did have a fuel problem i.e. (fuel Pump, Filter or fuel restriction and/or mother board?) Everything seem to check out OK so I went ahead and had oil, Filter changed plus replace Fuel Filter.
They ran it for 2 1/2 hours at the facility with a full load, running both A/C's, No Problem?
When I picked it up I also ran it for another 2 hours with full load and worked great, No Problems so to say what my problem was, don't really know but hope it works OK .

Thanks again for your responses as I did go back and correct my spelling on my subject so as to not confuse everyone?
DANO2014
Allegro Bus 2002
Retired: Cameron Iron Wks
U.S. Army Veteran
Louisiana Masons

FIRE_UP
Explorer
Explorer
DANO2014 wrote:
Having problems with my generator, Onan 7500....runs OK until I turn my A/C on. When it loads up the generator will run about 5-10 minutes and kill.
I am getting three blinking lights on the switch after stopping. According the manual it mentions abnormal maintanence problems. I will bring it to a Onan dealer in the morning but was checking on any suggestions available information from those that may have experience these issues.


DANO2014,
Ok, you're seeing "Blinking" lights on the switch after the engine shuts down. Those blinks are telling you a code. The code is deciphered by counting the amount of blinks you see, then, there's a short pause in the blinks then, there's anther set of blinks.

Then, there's a long pause, and the whole sequence starts all over again. So, first off, how many blinks in the first series, then, after the short pause, how many more. If you count say, three blinks in the first set, then the short pause and, three blinks again then, the long pause, you'd have "3 and 3". That would represent a code 33. In the trouble shooting book for Onan, there's a list of codes, what they all mean, and, possible remedies for each code. On my coach, an '04 Itasca Horizon 36GD with the C-7 330HP CAT, we also have the 7.5 QD diesel gen.

About two years ago, it did the same exact things yours is presently doing. When I checked the codes, it came up as "over heat condition" and, in the book, it had several remedies. All of which were not the cause.
What it ended up being was a very common cause of that code "33" (three blinks, short pause, 3 blinks- long pause, start over), and that was the infamous "TEMP SENSOR" that's located in the thermostat housing in that little Kubota 3 cylinder, 14HP diesel engine.
It's been known to cause all kinds of operational issues.

Now, does this mean that, that is your cause, not sure but, you'll have to decipher the code, to start. Good luck.
Scott
Scott and Karla
SDFD RETIRED
2004 Itasca Horizon, 36GD Slate Blue 330 CAT
2011 GMC Sierra 1500 Ext Cab 4x4 Toad
2008 Caliente Red LVL II GL 1800 Goldwing
KI60ND

2oldman
Explorer
Explorer
OK, you can change the post title anytime 🙂
"If I'm wearing long pants, I'm too far north" - 2oldman

glamisorbust
Explorer
Explorer
3 blinks usually means it's low on fuel. There is a fuel pickup in the tank about 1/3 of the way up from the bottom. Keeps you from draining the tank using the gennie. Make sure you have a full tank of fuel.
1999 Holiday Rambler Endeavor 38'. Cummins ISB 275, allison 3060.
Toys pulled: 22x8.5 open deck PJ flatbed. 5200# axles. Sand car with ecotec engine. Multiple 1980's ATC's(3 wheelers). We're duners!

DANO2014
Explorer
Explorer
Sorry for the misspelled word (Quite / Quiet) but my computer did it but thanks for the quick response which most are very helpful.
DANO2014
Allegro Bus 2002
Retired: Cameron Iron Wks
U.S. Army Veteran
Louisiana Masons

Kayteg1
Explorer
Explorer
With diesel you always start with checking for air in fuel lines.
Make sure everything is tight and solid.

2oldman
Explorer
Explorer
quiet
"If I'm wearing long pants, I'm too far north" - 2oldman