generator overheat, any ideas??
2004 holiday rambler.. 7500 onan diesel. Going down the road will run about 30-45 mins sitting in the driveway about 15mins then shut down...it flashes the 1 code then the 3-3 code for over heat shut ...
Forum Discussion
jtad,
Well Sir, after reading your posts and, all the others, I'd have to aim your issue at the temp sensor, located in the lower half of the thermostat housing. That temp sensor, has been the source of many "over heating" and "Starting" issues for many of the 7.5QD units as well as the 8.0QD units. The temp sensor is responsible for both cold starting and, over heat shut-down too. It is the about the size of a lawn mower spark plug.
Now, due to the environment that it sits in, it can get corroded somewhat easily. The top part of it looks like a normal temp sensor with a threaded stud on it, to hold the temp sensor wire. Now, the bottom section, the part that's inside the T-stat housing, is basic a copper cylinder, about 1/2" in diameter and, about 1" long. However, the bore that it resides in, is only slightly larger than the sensor portion itself.
So, due to the fact that there is very little clearance between the sensor stub and, the bore it sits in, there is very little coolant flow around that sensor body. And because of that tighter clearance, corrosion will start to develop all the way around that sensor stub until, it actually fills in the entire gap, around the stub.
When that happens, you now have no way for that sensor stub to detect just what's cold, hot, warm, anything. It will then start to send false readings to the little Kubota 14HP diesels ECM. It will tell that ECM that the engine is running hot when in fact, it's operating at a completely normal temperature. If you go into the Onan 7.5QD troubleshooting manual, you'll see that code "33". It will also tell you of the potential causes and remedies for this situation.
Some are:
1. Blocked air flow for the fan cooling system
2. Broken or missing water pump drive belt
3. Reduce the number of appliances on at one time
And the list goes on.
And, someone asked about the "fan" for the radiator. Well, the front of that little Kubota engine, faces away from the front of the coach. The only thing attached to the front belt system is the crank pulley and the water pump pulley with the belt in between. The actual fan that cools the radiator is attached to the rotor, which is attached to the flywheel, which is at the rear of the engine, which faces the front of the coach.
Now, that fan and, all the sheet metal around it and, all the panels, top, sides, front and back, and, a center bulkhead panel, is what controls all the air movement throughout that entire cooling system. You see, the fan draws air from the bottom side, through a grate/grill. The cooling airs first job is to cool the radiator. Right after cooling the radiator, it then cools the rotor, stator and all the wiring etc. in that immediate area. Then, that same air, is routed right though a hole in the partition/center bulk head, to cool the entire exhaust area, including thee muffler itself.
When that's all done, the air is jettisoned out the bottom of the generator, at the rear section, underside. So, the fan itself is not a normal looking fan. It's a rotary fan, similar to what's used in ducting and A/C units only thinner.
Now, also, that temp sensor is responsible for engine startup too. It tells the engine ECM what temp the coolant is. If it's real cold, as in way below ambient outside temps, it tells that ECM to hold the heat on the glow plugs for a longer duration. If the coolant is relatively warm or, mildly cool, the temp sensor tells the ECM that and, the ECM doesn't need to warm up the glow plugs.
So, after all this blabbing, I hope I've given you just a bit of insight as to what MIGHT be your problem. If, that temp sensor is corroded and, is giving you false readings and, causing the premature shut down due to "over heat" condition, you'll need to replace it.
And that my friend, can be one serious pain in the a$$ or, it can be as simple as changing a lawn mower spark plug. It all depends on just how corroded the temp sensor end is, and how long it's been like that.
A good buddy of mine on here, actually did a test/experiment of that temp sensor system and, it worked. His was doing the same exact thing as yours is, mine was and, many, many others. So, as an experiment, he purchases another temp sensor from the local Cummins/Onan parts house and, opened up the top cover of that generator. That exposed the area of the temp sensor and the electrical wire attached to it.
What he did was, remove the wire from the temp sensor, then attach it to the new temp sensor and, strap that new sensor to the thermostat upper hose. What that did was allow for the new sensor to send the engine ECM, proper readings.
IT WORKED!! That engine/generator ran like a top, all through running the A/C and other appliances without shutting down one time. Ingenious!! But, he only did it that way 'cause he was on the road at the time of the problem. When he returned home, he replaced that sensor properly.
Scott
Well Sir, after reading your posts and, all the others, I'd have to aim your issue at the temp sensor, located in the lower half of the thermostat housing. That temp sensor, has been the source of many "over heating" and "Starting" issues for many of the 7.5QD units as well as the 8.0QD units. The temp sensor is responsible for both cold starting and, over heat shut-down too. It is the about the size of a lawn mower spark plug.
Now, due to the environment that it sits in, it can get corroded somewhat easily. The top part of it looks like a normal temp sensor with a threaded stud on it, to hold the temp sensor wire. Now, the bottom section, the part that's inside the T-stat housing, is basic a copper cylinder, about 1/2" in diameter and, about 1" long. However, the bore that it resides in, is only slightly larger than the sensor portion itself.
So, due to the fact that there is very little clearance between the sensor stub and, the bore it sits in, there is very little coolant flow around that sensor body. And because of that tighter clearance, corrosion will start to develop all the way around that sensor stub until, it actually fills in the entire gap, around the stub.
When that happens, you now have no way for that sensor stub to detect just what's cold, hot, warm, anything. It will then start to send false readings to the little Kubota 14HP diesels ECM. It will tell that ECM that the engine is running hot when in fact, it's operating at a completely normal temperature. If you go into the Onan 7.5QD troubleshooting manual, you'll see that code "33". It will also tell you of the potential causes and remedies for this situation.
Some are:
1. Blocked air flow for the fan cooling system
2. Broken or missing water pump drive belt
3. Reduce the number of appliances on at one time
And the list goes on.
And, someone asked about the "fan" for the radiator. Well, the front of that little Kubota engine, faces away from the front of the coach. The only thing attached to the front belt system is the crank pulley and the water pump pulley with the belt in between. The actual fan that cools the radiator is attached to the rotor, which is attached to the flywheel, which is at the rear of the engine, which faces the front of the coach.
Now, that fan and, all the sheet metal around it and, all the panels, top, sides, front and back, and, a center bulkhead panel, is what controls all the air movement throughout that entire cooling system. You see, the fan draws air from the bottom side, through a grate/grill. The cooling airs first job is to cool the radiator. Right after cooling the radiator, it then cools the rotor, stator and all the wiring etc. in that immediate area. Then, that same air, is routed right though a hole in the partition/center bulk head, to cool the entire exhaust area, including thee muffler itself.
When that's all done, the air is jettisoned out the bottom of the generator, at the rear section, underside. So, the fan itself is not a normal looking fan. It's a rotary fan, similar to what's used in ducting and A/C units only thinner.
Now, also, that temp sensor is responsible for engine startup too. It tells the engine ECM what temp the coolant is. If it's real cold, as in way below ambient outside temps, it tells that ECM to hold the heat on the glow plugs for a longer duration. If the coolant is relatively warm or, mildly cool, the temp sensor tells the ECM that and, the ECM doesn't need to warm up the glow plugs.
So, after all this blabbing, I hope I've given you just a bit of insight as to what MIGHT be your problem. If, that temp sensor is corroded and, is giving you false readings and, causing the premature shut down due to "over heat" condition, you'll need to replace it.
And that my friend, can be one serious pain in the a$$ or, it can be as simple as changing a lawn mower spark plug. It all depends on just how corroded the temp sensor end is, and how long it's been like that.
A good buddy of mine on here, actually did a test/experiment of that temp sensor system and, it worked. His was doing the same exact thing as yours is, mine was and, many, many others. So, as an experiment, he purchases another temp sensor from the local Cummins/Onan parts house and, opened up the top cover of that generator. That exposed the area of the temp sensor and the electrical wire attached to it.
What he did was, remove the wire from the temp sensor, then attach it to the new temp sensor and, strap that new sensor to the thermostat upper hose. What that did was allow for the new sensor to send the engine ECM, proper readings.
IT WORKED!! That engine/generator ran like a top, all through running the A/C and other appliances without shutting down one time. Ingenious!! But, he only did it that way 'cause he was on the road at the time of the problem. When he returned home, he replaced that sensor properly.
Scott
