Not sure if it is the same on the QD7500, but on the QD8000 the Temperature Sensor is known to go out and result in a 333 error code, running hot... In this case, the generator is not actually running hot, but when the sensor goes out, it comes the connection to the brain which looks to it as if the sensor is sending a High Temp.
We replaced ours twice. The last time, we had a second temp sensor A/B switched into the mix. With the secondary sensor hose clamped to the mental intake of the hot water return into the generator.
So this way, if the OEM placed Temp Sensor again fails. I can validate that fluids are in good shape, check the belt is good, and oil levels are also OK. If so, I will then switch over to the alternate Temp Sensor, allowing continued use of the generator. Yeah, I'll replace the OEM located Temp Sensor again too, but on my schedule - as opposed to running up Highway 395 and having the generator shut down in Bishop with 112 degree bank temperature flashing down at us
If any of you do this, please note that you are assuming the risks, and you also should do regular checking of all vitals while using the alternate temp sensor. (I have not had to use this yet
! But, I do test it about every three months, to be sure the "B" alternate Temp Sensor still is working too.)
And another common problem with these units, is neglecting of testing the coolant, and keeping the smaller radiators cleaned. We had to replace our generators radiator, even flushing would not get it unclogged. (Bad maintenance from previous owner.) We had Final Charge OAT based coolant added to the generator radiator, same as we run in the coach, for ease of carrying only one kind of spare coolant. The bonus, is I feel the generator is running a bit cooler then it had on regular coolant.
Best to all,