Hey guys, just a quick question. Bought a Merc 525 353 Fastech. Currently has 310 hours. While running at 3600 RPM everything seems fine 165 to 175 degrees. After running about 15 miles to come back in to my marina, when I come off plane and am idleing in the oil temp went up on both motors to 180 on port and 200 on starboard. Never went above these temperatures and they went back to 150 when I got it out of the water and flushed it on the work rack. Is this normal?

200 is on the cool side but I wouldn't personally worry. it'll come up a little when you run it harder and when the water you run in get's warmer during summer.

Mine run 180-190 when up and running, often off plane in a hurry they will go up, 200+ but will come back down shortly. Many years back I did call Merc Racing tech and was told not at all out of the norm. Water temp on mine are very stable, seldom vary at all.


While on the subject here, has anyone changed out the Merc sea water pumps in favor of after market two stage pumps? I am doing my 525's right now and had this very conversation with my engine guy last Friday about some billet two stage pumps and whether they might be worth the money. Any thoughts here??????

I had a two stage pump on mine, but the second stage or half of the pump was used for the intercooler. Are you talking about running both stages through the motor? That’d be way too much pressure

Was somewhat my thinking as well, he just threw it out there in conversation. Another customer of his had him install after a rebuild on a 496 Mag HO last summer on a Sunsation 32. He just mentioned it, wondered if it might be something I would want. Much easier when they are out than when back in the boat. His other customer used the Hardin two stage pumps.

I was just looking for some input here.

^^^ this. There's no need for a two-stage pump on a stock 525. As long as the impeller is good and the raw water passages are all clear, the standard water pump does the job just fine.