I recently bought a used Howard with a 525. When I first start the boat ( and crusing along for 10-15 minutes) the oil temp will climb to approx. 240-250 degrees for about 5-10 minutes then drop down to around 200-210 per the analog guage. Is this normal? Does the oil thermostate need to be changed? The water temp never goes above 170 on the analog guage and 153 on the Mercury Smart Craft. I don't think I have oil tempeture capabilities on the Smart Craft. Or at least I haven't been able to find it yet. I also noticed it seems to rise again when just idling. Can you check the temp acurately with a laser temp meter on the filter?

From what I've seen with 525's, high oil temps have been caused by leaky headers (internally) the water contaminates the oil packing up the filter and by-passing the oil cooler. It was the first sign of leaky headers.

I Had the same problem with leaking headers but the oil temp building up and then cooling down is normal for the oil thermostat.

My oil temps fluctuate, but rarely go above 200 and usually hang arounf 180.

The water temp doesn't seem to fluctuate at all and the oil pressure seems to stay constant as well.

Maybe it's just the thermostate opening and closing causing the fluctuation? It just alarms me seeing the temp get to 240 on the guage.

What does the oil temp climb to on a wide open run?

The oil temp doesn't climb at all at wot. I usually only keep it wide open for 20 seconds or so though.

240 F isn't all that hot, modern day oils can handle that all day long.

180 F may be on the low side to evaporate any condensate out of the oil though.

Ken

Before you go crazy chasing perceived high oil temps , get a non - contact temp gun and check it that way , at various locations ...

That's what I was thinking of checking. Is the filter the best place to get a reading?