Erratic Temp Gauge 2007 FG140 4m50 engine.

Hello from Alaska. We are 500 miles from home and first though our engine was overheating.

We have a 2007 FG140 and 4m50 engine. My engine temperature gauge is all over the place.

The condition feels like instrumentation because the gauge instantly reads normal after cycling the ignition and pegs hot when simply reving the engine at idle then return to normal.

We got the off the road at 2330 last night and I’m jumping into it further this morning, but it feels like a sending unit problem. B3C1F814-E73B-49CE-9B68-922608F686EB.jpeg

Has anyone else had a condition like this?

Thank you in advance.

*picture for effect
 

Czechsix

Watching you from a ridge
I'd look into connections and grounds first. I didn't have that issue on our FUSO, but I've had it on various other vehicles. If you have the shop manual you'll find the measurements to be able to test the sender and verify whether it's good or bad.

But I'll bet connections and grounds. Other thing that can happen, come to think of it, is if your voltage is low. You'll get all sorts of weird effects when that happens. Might want to check battery, battery connections.

I passed you guys when you parked outside Cantwell, lol.
 

lanceatm

Founder and CEO of EarthCruiser
Hello from Alaska. We are 500 miles from home and first though our engine was overheating.

We have a 2007 FG140 and 4m50 engine. My engine temperature gauge is all over the place.

The condition feels like instrumentation because the gauge instantly reads normal after cycling the ignition and pegs hot when simply reving the engine at idle then return to normal.

We got the off the road at 2330 last night and I’m jumping into it further this morning, but it feels like a sending unit problem. View attachment 602213

Has anyone else had a condition like this?

Thank you in advance.

*picture for effect
There two temp senders on the 4m50. One you see one the CPU sees. Running a new earth wire from cab to chassis often solves the problem ( it was a recall item in 2008 by memory) for one we can see . The clutch fan is often the culprit if the truck is indeed getting warm. My guess is the earth wire.
 

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biggoolies

Adventurer
Hello from México. Mine does that too. 2006 fuso. Sure makes you sweat doesn’t it! Especially in the Mexican heat in the middle of nowhere. Am I going to be stranded? I would like to solve that problem too but in the meantime if I were you, set up a seperate temp meter. You require a long cable due to the cab over like at least 12 feet. Also when you solve the problem you will also be able to monitor engine temperature twice and not rely on only one.
 
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