Generator breaker tripping while driving

[Steve Pillon]

Been having a problem with the generator ( onan 7.5 ) on my 89' marquis, while driving in warm temps ( over 85 degrees outside ) we run the genset and run the front AC. After about 45 minutes the genset temp guage inside coach climbs to about 230 degrees and throws the output dual breaker on the genset.  Just tooh it to cummins/ onan in South Carolina had the radiator boiled out, new water pump, new hoses, new sensor and was assured the problem was solved!  Got about 60 miles away running the genset on a warm day and breakers trip. Took back to cummins they tested the genset every way and could find no problem with genset and no solution for problem!  Being this only happens when traveling in warmer weather I'm thinking the problem might have to do with air flow into the genset compartment but I've been told this would have nothing to do with tripping the breaker.  One more thing the genset does not shut off when breaker trips it keeps running.  HELP?  Thanks Steve Pillon

[Steve Huber Co-Admin]

Steve,
If your gen set is located on the rear driver's side, with the engine exhaust pipe outlet just rear of it, install a chrome tip on the engine exhaust and angle it about 45 degrees to the rear. I had same problem on my 01 Contessa and this fixed the overheating permanently. (I live in AZ so got lots of chances to verify the fix). The problem is that when moving  the coach sucks the hot exhaust back under in the area of the genset air intake.
Steve

[Stan Simpson]

Steve,
If your gen set is located on the rear driver's side, with the engine exhaust pipe outlet just rear of it, install a chrome tip on the engine exhaust and angle it about 45 degrees to the rear. I had same problem on my 01 Contessa and this fixed the overheating permanently. (I live in AZ so got lots of chances to verify the fix). The problem is that when moving  the coach sucks the hot exhaust back under in the area of the genset air intake.
Steve

Wow! And the Cummins/Onan people didn't know that? Or suspect that? Not good.  :-/

[Edward Buker]

Steve,

I believe there is a belt driving the fan on your model and I assume that they changed the belt also. Slipping causes overheating and shut down if you have sensors that monitor for overheat. As far as the breaker tripping with heat, that issue may be internal to that breaker. If there is no reason for an overcurrent condition and the breaker just trips I would be sure and change out the breaker. The contacts and the springs age and wear out given these are mechanical devices and heat accelerates the aging of the springs.

Later Ed

[Steve Pillon]

The generator sets behind the left front tire and the exhaust runs out the back of the coach. Cummins replaced the fan belt and did a load test on the breakers and they held on a 10 amp overload test and they felt the breakers were good. I think I'll try a fan on the fresh air inlet of the compartment to see if some more airflow will solve the problem.

[Edward Buker]

Steve,

I have the 10kw version mounted on the side of our coach so the results may not be exactly the same but this may help. It sounds like they did a lot of work on the cooling system. Did they change the thermostat? You can get some good diagnostics using an IR gun. Shoot the face of the radiator in multiple spots to see if the face is reasonably uniform in temperature as it comes up to temp. You can see if it stabilizes as if the thermostat opens properly. You can pull the side cover momentarily and shoot the oil pan and a spot on the block water jacket and close the cover back up. These are some references if the cooling system is working properly. The oil pan should be about 150 degrees and the radiator face about 120 degrees if the belt is doing its job. The radiator was 188 to 217F across the finned area measured from the bottom, the oil pan was 206F, the engine block was 215F when mine was overheating due to a slipping belt. Your 230 degrees sounds to me like a stuck thermostat or a slipping belt. They may have changed that belt but is it tight enough would be the question. The breaker can handle the current when cool but may be heat sensitive at these temps. If it still trips once the temperature problem is sorted out then I would not hesitate to change it.

Later Ed

[Gerald Farris]

There seems to be a little confusion here in comparing the enclosed cabinet model QD Series (quiet diesel) to the open design 7.5 series that was used in the 1989 Marquis. In 1989 the generator was in an enclosed bay for sound proofing and did not have its on sound proofing housing. Therefore Steve's idea of furnishing more air to the compartment may be a valid point.

The 230 degree temperature is definitely too high, and if the problem is a mechanical problem with the generator it should be able to be duplicated when sitting still with the bay closed. I find it hard to believe that the problem is a design problem with the compartment air flow that has existed for 24 years before it caused a problem. Therefore I would load test the generator with a moderate to heavy load while sitting still with the compartment closed to see if you can duplicate the problem, and if so you should be able to determine the root cause.

Gerald    

[Steve Pillon]

Thanks Gerald, the problem has been ongoing for a while but only happens on those hot days!  We just recently retired and are using the coach more often and for longer period of time. We been traveling for two months now and have encountered some 90 to 100 degree days driving in the hottest part of the day. We were in Gilette with the fmca rally and had some 90+ days and ran the generator for a couple hours with no problem being parked, but start driving in those temps I get about 30 to 45 minutes and the breaker trips

[Steve Huber Co-Admin]

Steve,
Sure sounds like incoming air temp or lack of airflow. When driving, the incoming air is already heated by the pavement which you can't duplicate by running in place. I'd verify a clean radiator, and tight belt per Ed. Also, check on  any work done recently that might change the airflow under the coach in front or near the gen set radiator.
I don't understand why the gen set keeps running at 230. While I don't have the manual, I would think this temp would trigger a shutdown and cause it to flash an overtemp code.
Steve

[Edward Buker]

Steve,

Even though they load test the breaker you can still get a temperature sensitivity due to heat as the contacts age (become more resistive), and the springs age. They should not be that expensive and a new one rules that possibility out. I still think you can learn a lot with an IR gun and these liquid cooled diesel generators. First you could learn if 230 degrees is real and if obviously that is overheated. You can see if the radiator and the water jacket are similar in temp indicating good circulation. You can tell what the thermostat is doing by shooting that and see if it looks like that is opening when it should. If air flow is poor the radiator face will have hot spots and it will be more uniform if there is good airflow and antifreeze flow.  It may take a little interpretation as to what is going on. There needs to be good cool airflow incoming to the radiator face and a good exhaust air flow from the compartment ideally without mixing the two. If you have lost some air dams or shroud sealing of the inlet air that could come into play here. Gerald pointed out that you do not have a generator enclosure from Onan with this configuration but the principles are the same. Steve is thinking airflow. If you know of another coach that has a similar genset you may be able to IR gun that one to see what is different. If you resolve the overheating issue you might want to consider an oil change, the oil will reach temps in excess of the water jacket sensor and may become degraded due to oxidation. It is cheap insurance.... Hope this helps.

Later Ed

[Larry and Heidi Lee]

Would it make any sense to extend the generator out about 4" and perform the road test to see if the addtional airflow keeps the genny cooler..? At least until you figure it out..

[Gerald Farris]

Larry,
The generator on a 1989 Marquis is in the bay behind the LF (left front) wheel, and bolted to the frame. Therefore, there is no way to "extend" the generator for a test.

Gerald

[Steve Pillon]

Ok here is an update on my ongoing generator problem today I drove 60 miles and the outside temp was about 85 degrees, shut all interior breakers off, the inverter off and left the front air breaker on and ran the front air and it tripped the breaker! Then stopped reset the breaker and waited for 15 minutes running the generator and AC while paked and the temp went down to normal! Repeated with just rear AC and the same results! So I am going to change the breakers on the generator and install a fan on the air intake to help force some fresh air into the compartment will post the results later.  Thanks for all the suggestions. Steve

[Steve Huber Co-Admin]

Steve,
The breakers may be weak due to heat but I don't think that will solve the problem as they passed Cummings' overload test. Adding a fan to increase airflow should help a lot, IF it is pulling air in under driving conditions. Another thought would be to add a scoop to channel the air. Only downside is that it may also bring in debris. I'm still confused as to why it isn't flashing a code at 230. We're messing something.
Steve

[Steve Pillon]

This is the older unit 1989 it does not have the electronics like the new units, just breakers and reset buttons.