I have a 1999 Motorhome on the F53 chassis with 275hp V10. I'm having a problem with getting false high temperature readings which puts the engine in the "limp" mode. This happens at any time including after just driving a couple miles to being on the interstate driving 65 mph. I use a scan gauge II which gives a reading that can go from 200 degrees to 255 in a matter of 30 seconds or it can slowly climb to 255 over several minutes. I have pulled and checked everything with no sign of actual overheating and have used an IR temperature gun which shows normal temperatures.

I have read every thread on this forum that mentions false overheating, but no one ever posts what they finally did to solve the problem. So far I have replaced the water temp sensor and the thermostat with no change.

Any recommendations will be highly appreciated.

Thanks, Bob

 

Have you replaced the temperature sensor in the left head that does not sit in coolant?

 

Is that the Cylinder Head Temperature Sensor? I tried to locate it but not sure exactly where it is. When you say the left side, do you mean the drivers side?

 

Yes, take the alternator off and you can access the sensor on the drivers side in the valley near cylinders 5 & 6.

 

Right now I'm in a campground and taking the alternator off in a motorhome is a real pain so I might have to wait till I get home. I see the connector going to the sensor but I can't even get my hand in to touch the sensor. Any idea what would happen if I disconnect the sensor? I'd like to be able to get home without going into limp mode every few miles and I know for sure that the engine is not overheating so I'm willing to risk driving with sensor disconnected.

I'd even be willing to buy a sensor and connect it and just lay it on top of the engine just to get a "normal" reading.

 

"I'd even be willing to buy a sensor and connect it and just lay it on top of the engine just to get a "normal" reading."

Sounds like a plan, let me know how it goes? Maybe tape it to the water crossover?

 

I've heard of this exact thing before, don't be surprised if it's the computer. Change the sensor, chase all the wiring to be sure, but ...

 

I think you may be right. I drove to the next campground (220 miles) and the temperature fluctuated between 206-242 and mostly stayed close to 224. My IR temp gun registered 190 at the temp sensor and a little lower when pointed at the upper radiator hose. At least it never went into limp mode.

I'm thinking about buying an aftermarket water gauge so I can know what the temp really is. I will unhook the old gauge and hook a rheostat to the wiring harness so I can dial up a temp that matches the "real" temp. I still have a month on the road before I get home and have the resources to do more, so this may work in the short term.

I did program my scan gauge to show the cylinder head temp and it fluctuates right along with the water temp- always staying about 2 degrees higher, so I don't think its the CHT.