Temp gauge goes cold sometimes when raising rpms. Both when warming up and at temp from hours of highway driving. Around 2-3000 rpms you typically see problem. The higher I raise rpms, the lower the temp goes, sometimes it will read dead cold. Problem mostly occurs in gears 4-5, Between speeds 45 and 80, up hill, flat road or down hill and in hot climates or cold, at sea level and 2500 ft elevation.
Also when I hit a bump in the road, the temp will drop for a split second.

First I simply burped system.
Then I Replaced thermostat and leaking radiator overflow hose (pinhole leak).
Problem disappeared for a few hours. May have been fluke.

Thinking it could be temp sensor (pretty sure prev. owner told me 1 of 2 sensors were bad already), Check engine has illuminated twice in past year, I simply pop hood and fiddle with temp sensor at rear of engine near firewall (has bad clip so it gets loose sometimes) and check engine goes away. Before you say, new sensor...

When my check engine comes on, my temp gauge remains at operating temp, leading me to believe it isn't temp sensor causing gauge to show cold intermittently.

Also thinking water pump could be going. I haven't replaced since I got truck four years and... About 60,000(+?) ago.

I've done alot of work myself on this truck but this has me kind of stumped and I don't have the time or energy to diagnose and fix the wrong thing again at this point in time. She's my only way to work and my daily driver/entertainment.

Need to get my trusty horse back in fighting shape asap!
If you can help me out and you're in my area (live in Seattle area, work in Wenatchee area) I'll buy you some



Thank you thank you!

 

Almost certainly not a problem that would be associated with engine or cooling system mechanicals like water pump, ect.

It is an intermittant electrical instrument issue.

Check, clean, and improve all engine and body grounds before anything else.

 

I'll give em some attention.
Hope that's what it is.
Results soonish.
Thanks

 

Definately electrical. Try running a new wire from the sensor to the dash? Could have rubbed trough somewhere causing the issue

 

At first I thought the problem went away on its own during a hard drive over the pass after waking up 2 hours late. Then it started up again. Radiator cap was leaking. fixed that. Temp gauge problem persisted. Poked around at coolant temp sensor near firewall and made sure it was on tight. No more fluctuating temp gauge.

Tl;Dr
Yous was right. Electrical problem. Loose connection at temp gauge. Thanks for lead!

 

The sending unit for the temperature gauge is not the coolant temp sensor!!

These are two different things !!!!!

If the coolant level drops so the sending unit is not in coolant strange readings will occur .

Engine rpm could effect this.

So could a loose or corroded connection at the sending unit