Innaccurate Temperature Gauge

Keith Browning · December 18, 2014

We recently had a 1999 F450 in to install a Jasper engine that was in the dump body when it was dragged in. The tech finished the install and observed the temp gauge as pinned hot, then started to fluctuate hot to cold hot to cold then stayed on cold.

Long story short it ended up in my bay.

It got a new ETC sensor and connector. I verified the parts.

Performed the diagnostics in the WSM and verified both circuits every which way. The PPTs led to replacing the ETC sensor. Hmmm. I executed the tests again with the same result. Even load tested both circuits. IDS active command modes had the proper response, command cold, it read cold. Command hot it read hot. In my time looking at this truck, the gauge would read just above cold when stated and quickly rise as it warmed up then pegged the hot mark and then fell to cold. Tried a different cluster - same problem. Verified the cluster power and ground circuits. Verified battery cables, body grounds to the frame, batteries and engine. All good.

Anyone ever see this?

8WA Sman · December 18, 2014

No other 5 volt sensors reading funky? Wire didn't get crossed when the pigtail was put on and terminal tension on the ECT is fine? Did the 42 pin harness on the left VC get checked for wire chafing?

mchan68 · December 18, 2014

Another temperature sender? New doesn't mean good. I'll assume you have verfied actual engine temp via an alternate method of course.

Keith Browning · December 18, 2014

To repeat, I tested the wiring thoroughly and oddly enough as you mentioned the tech did reverse the wires on the pigtail which I corrected. But that makes no difference.

Mike, I did grab another sensor... Same deal

Buddy_M · December 18, 2014

Correct thermostat for the application(not an 95ish early style in the late engine?) Thermostat didn't get installed upside down somehow or just a sticking tstat?

Keith Browning · December 18, 2014

Engine is reaching full operating temperature - EOT confirms 195+ and the heat is hot

This is definitely a gauge problem.

Putting 5K ohms into the circuit with my gauge tester dials it into the proper range.

jimmy57 · December 18, 2014

What voltge is on Signal Retrun wire to cluster? It stays stable while the gauge does the swings?

Bruce Amacker · December 18, 2014

+1 on what Jimmy says, the yellow/red wire should be under .05v at all times. If I were working on this I'd do voltage drop tests on the grounds, checking the dash, engine block, body, etc vs B- which should all be under .05 also. Does it do it KOEO also? Check ACV running to rule out the alt. Also, pull the battery cables and load test the bats individually. In my experience the dash complains loudly when there's a bad battery.

I had a 99 7.3 that had a really weird problem years ago. The turn signal circuit was bleeding voltage though the primary wire insulation to the adjacent CMP signal wire causing the engine to surge with the turn signal on. I told the guy he needed a harness but I put polyloom on the CMP wire to isolate it which cured the problem. I was where you're at- switched cluster, verified harness, etc, over and over again. More than a couple of hours in that truck.

Good Luck!

:grin:

Aaron · December 28, 2014

Are you using a ford or aftermarket sensor?

Make sure the sensor specs out for a truck with a gauge not a light also. Had both situations happen to me before.

Keith Browning · December 28, 2014

Aaron this was a Ford sensor which incidentally applies to ALL available engines, gas and diesel for numerous model years.

There had to be something else wrong with the truck but I will likely never know despite my efforts to look outside of the gauge operation itself. The gauge was adjusted to operate in an acceptable manner by installing resisters into the circuit. Not a real repair but this is what was decided and well, it is working, for now.