Bad Temperature Sender ?

[mike456]

1992 5.7L Mercruiser raw water cooled. new outdrive last year (although this problem was happening prior to that)

My temp gauge runs up to to about 150 at idle (its a 140 T-stat) but will then runs very erratic at high RPMs. It will sometimes run up to 200 and back down to 140 in a matter of 2 or 3 seconds. Today running steady at 3200 RPMs temp moved from 130 to 190 and back within about 30 seconds. I have checked the risers at full thottle and they are only slightly warm to touch so I do not think the engine is overheating. Is that a correct assumption? If so do I have an electical problem?
I checked and tightened all connection on the temp gauge. T-stat and housing are new this year. How likely is it that temperature sender in the t-stat housing is bad? The part is $50 so I hate buying one on the "hope" that is my problem. I know they work off of some resistence process but not sure if they are likley to (or can) fail.

Any advice will be appreciated.

 

[jerryjerry05]

Re: Bad Temperature Sender ?

Raw water cooled and in salt water it's possible the circ pump is bad.Do you flush it after using it in salt water?
The connections on everything should be checked.Back of the Gage,the grounds.Remove sensor and clean it maybe it's corroded.
I had a Mercruiser with overheat problems from the factory.It wasn't getting hot just the Gage going nuts.Looked and looked and finally found a wire was pinched in the harness going to the dash.
At home depot they sell a temp gun.It's a good tool to tell if your really overheating.J