erratic oil temp.
 

Hi,
I hope someone could help me with a problem that has been occuring the past few times I've used the boat. It's a fountqin with stock twin 7.4L engines.
The port engine runs the following once it warms :
water temp at 180 F
water pressure at 10-20 psi
oil pressure 25 at idle, 50 psi running 3000-3500rpm
oil temp is erratic, will set at 220 F and rise to 290 F and fall back to 220 f or may hold at 290 F.
Oil looks good, no burning, no discoloration etc. Everything sounds good.
Cannot find the sending unit on the engine.
Suggestions ?
ed

Can anyone tell me where the oil temp sending unit is located on a stock 7.4L mercruiser ?
ed

Are you sure that the oil temperature gauge is stock?

I was looking at some Merc diagrams and all I see is an oil pressure gauge and sender I also do not see it listed in the color code for wiring.

If it's not stock, you can pull the instrument cluster and look at the color of the wire that's hooked up to the gauge and then trace it back.

Generally, I think they are located in the oil pan.

I would agree that an oil temperature sensor is not standard on that engine. I agree with the comment to trace the wire from the instrument back to the engine if you can.

7.4s don't come with oil temp from merc but Fountain adds them. Most commonly the brown/ white wire is used for oil temp. The sender is easily installed at the filter adapter. My guess is its a loose connection or maybe the sender post is loose. By the way 290 is hot but not enough to worry about.
Jim

Thanks everyone. I'll try to locate the brown/white wire and check the connections at each end.
ed

By the way 290 is hot but not enough to worry about.
Are you serious ??I would shut it down if it goes past 245......

oil hasn't warmed up until 200

correction according to 525 service manual don't operate at wot until oil reaches 140 and manual states 220 is max allowable.
I raced these motors and that is unrealistic. By the end of the race they are up near 300. A merc engineer once told me at a race sight 275 is OK 300 is too Hot. 4 years in factory 2 every race oil temp was pegged near 320 at end of race
Jim.

At 300F you should be looking for ways to cool the oil. A Group IV synthetic can live at these temps, a petroleum based oil should be changed in 1/2 the normal drain interval.
ie:normal 25 hours, change it in 12-13 hrs.
Oil would be happier below 300F.
Ken