oil temp sensor questios

[TCEd]

I have a rather tame 1996 32' Fountain with twin STOCK MERCRUISER 7.4L engines. There are engine oil temp. sensors at the lower left rear on each block (somewhat buried)that were installed by Fountain not Mercruiser and the associated oil temp. gages in the dash.

My problem is the port engine has an erratic gage or sensor. The temp at times will hold in the low 200 degree range and at other times it will rise into the 280-290 range. Occasionally it will rise gradually and suddenly drop back to low 200 range.

I've flushed the oil cooler and hoses and that path is clear. This has been a reoccuring problem for three seasons so I'm guessing it is an electrical glitch no a oil flow issue. I check my oil before/after each outing and no discoloration, bad smell or consumption is seen. Oil is changed each season along with the filters.

How would I fault isolate this issue ? and could there be a thermostat on the block in the oil system I'm not aware of ? The filter mounts don't contain any sign or space for a thermostat.

Thanks for any and all help,
ed

 

[Trim'd Up]

I wouldn't think that stock 7.4's would be running almost 300 degrees oil temp unless something is wrong. Why don't you just switch the wires on the back of the gauges. It would be an easy way to see if it is the sender or the gauge.

 

[Airpacker]

I wouldn't think that stock 7.4's would be running almost 300 degrees oil temp unless something is wrong. Why don't you just switch the wires on the back of the gauges. It would be an easy way to see if it is the sender or the gauge.

Sure would be easier than accessing the senders. If the problem stays the same, its a wiring or gauge fault. You could make up a set of jumpers to bypass the wiring harness for testing purposes to prove the harness.
If the problem moves to the other gauge, get a new sender.

 

[TCEd]

Trimed up & Airpacker,
Thank you for the fault isolation path. Makes sense.
I'll give it a try tomorrow evening and report back.
ed

 

[Griff]

I had a water temp guage doing the same thing. It was a bad guage. I agree, swap the guages or guage wires if they are long enough.
That does seem like a wierd place for the oil temp sender though. Probably not all that accurate anyway.