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Old 10-06-2015, 03:38 PM   #15
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Originally Posted by Gary RVRoamer View Post
I ran into the above "nightmare" scenario helping a friend change his QD 7500 temp sensor. He & I worked on it the better part of a day to get the old, seized and broken sensor out. Both of us are mechanically skilled, and had plenty of tools for the job, but it was still a challenge.

And sometimes the sensor isn't even accessible without yanking the genset. All depends on how the coach front end is set up, e.g. gen slide-out, large or small access panel, etc.
The Horizon and the Vectra of that year, both had slide-out generators. Having that option, sure makes ANY work/maintenance SERIOUSLY EASIER. But, like yours, that particular repair, even with the slide-out feature, gave me a ton of grief.

A short story. I attempted to get that sensor with the use of socket and ratchet but, NO GO. So, as you know, there's very limited room in there for alternate type tools. So, I figured what the heck, let's dismantle what I have to, to get better access to that sensor. Well, half-the-generator apart later, I put a long handled wrench on it and, as you can see, it broke the sensor. CRAP!

So, out comes the PIPE WRENCH. Still a no-go. So, I came up with this bright idea of "freezing" the sensor. Off to the store for a can of "Freeze". I used a propane torch for the area immediately surrounding that sensor and then, immediately cooled what was left of the sensor for only a few seconds.

I put my vice grips onto what was left, and, that stub, un-screwed right out. And you can see what was inside that cavity where the sensor lived.

Anyway, I cleaned out the threads, replaced the sensor, put the mess all back together and, uh-ohhhhhh, what's this, A MAJOR COOLANT LEAK!! I thought I'd securely tightened all the hose clamps thoroughly etc. Well, could not see where it was coming from but, it was pouring out.

Well, with the use of a mirror, I found it. What happened was, (and I hope the OP is reading this) when I was applying that much torque to the sensor, with all the various tools, I cracked the thermostat housing and, didn't know it.

So, most of that generator had to come back apart, including pulling the engine head, to gain access to that t-stat housing to remove it. I was going to TIG-Weld it up when, a new one could readily be had for a whopping $54.00. Back down to Cummins/Onan I went for that and, a head gasket.

All back together and, is running well. What a pain. All for a $17.00 sensor.

OP, do take care if and when you find out you need to replace that sensor.


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Old 10-07-2015, 03:32 PM   #16
Join Date: Jul 2011
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Thanks for all the info. guys I have not had time to get to it yet. Will start with fuel and air filters I hope its not the overtemp. sensor that does not look like fun

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Old 10-08-2015, 07:10 AM   #17
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Just a shot in the dark. I've related this several times by my 7500QD on the last coach kept shutting down and throwing overheat codes. Not on a slide so it had to be dropped. I had EVERYTHING replaced so I would not have to continue to drop it. Didn't work. It would shut down if you loaded it heavy. Long story short after dropping and spending many hours & days testing it was a defective radiator cap. Wasn't holding the correct amount of pressure. I'll never know if that was in fact the original problem but it's cheap to try it. Good luck.

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Old 10-09-2015, 03:57 PM   #18
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Thanks Duoglide1 I am picking up a radiator cap as well not leaving for AZ for another month I have a little time

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