Gauge, sending unit or wiring problem

When my truck is started, my temp gauge goes directly to about 100 degrees and climbs to 240 within 3-4 minutes. I've checked the engine with a thermal thermometer and it reads about 165 degrees.

I updated the truck during the last 3 years and prior to that the gauge and sending unit worked correctly. I'm also using the same wiring harness as before. To figure out the problem, I replaced the sending unit with a new one. Same problem. I then hooked up another temp gauge and it did the same thing.

I was going to check the resistance in the sending unit wire but can't find my ohm meter. I'll pick one up tomorrow. Any idea what is wrong or what I may have done to cause this?

A possible related issue is that the oil pressure gauge pegs to the right when the engine is started. Part of my update included a rebuilt engine that I bought in 1999 and has been sitting since then. It runs great and sounds good but the oil pressure concerns me.

Thanks,
Bob

 

Sounds like a bad ground, one gauge grounding into the other. Check dash grounds, engine to body grounds. Does the problem change when the dash lights are on?

 

As I recall, I used a common ground for all of the dash gauges (back in 1998). I do have an engine to body ground along with a body to frame gound and a engine to frame ground. I turned on the lights and the temp gauge did not change. The oil pressure gauge moved about 1/32 of an inch to the left. Bob

 

Mine did basically the same thing. Turned out to be a bad ground from the gauges to the body. Make sure the gauges have a proper and clean ground path.