temp gauge jumps between 175F and 250F

[Searay87]

The Faria temperature gauge on my 87 sea ray seville 17BR 3.0L mercrusier jumps back and forth (instantaneously) between 175F and 250F with a delay of about 4-5 seconds (re :reads 175F for 5 secs then jumps to 250F and stays for 5 secs). I've checked the actual engine block temperature with my handheld non-contact IR thermometer and the highest temp I measured was 176F where the water exits the block into the exhaust manifold. I'm thinking this is an electrical problem. I replaced the thermostat and the sending unit at the end of the season last year and all was well at that time. I've removed, cleaned and tightened the connection on the seding unit. Has anyone experienced this problem? Any thoughts on what else I can check?

Thanks!

 

[EddiePetty]

Re: temp gauge jumps between 175F and 250F

With the ignition switch to "Run", remove the lead to the sending unit and touch it to ground. The gauge should peg to highest; un-ground the lead and the gauge should peg to lowest.

If the gauge tests sat., I would suspect a short to ground anywhere along the cable run.

(By any chance did you use any type sealer on the sending unit's threads?)

 

[Tool819]

Re: temp gauge jumps between 175F and 250F

I had the exact same problem.Tested the gauge by grounding sending wire.Gauge pegged and then removed it and dropped right off.Ran new ground,sending wire,replaced thermostat and sender and still did the same thing.Turned out to be a bad gauge.Was tracking to ground on connections inside gauge somehow.Try changing it and see what happens.

 

[Stamey]

Re: temp gauge jumps between 175F and 250F

Sounds like a bad gauge to me also. Every now and then a bad ground in the gauge cluster can cause the alternator/voltage regulator to cause the gauges to do weird things because they are back-feeding through the gauges due to the bad ground someplace else in the cluster. This can be difficult to track down. I'd chase the gauge being bad first.

Chris

 

[Volphin]

Re: temp gauge jumps between 175F and 250F

There are two wires on the back of the gauge. Your connection is loose. Be careful of grounding out the wire at the sender to peg the gauge... you can damage the reactionary coil or bimetallic strip by overheating it. Some nice dielectric grease will keep this connection happy.

V