We had 1 of our 572's start running about 20 degrees hotter than the other engine and verified it with a heat gun. First thing I noticed was that the back of the block was 50-60 degrees hotter and the dash temp gauge was going up and down between 120-180 at higher speeds. Both symptoms we battled with crossovers so I went right to the circulation pump. The vanes were gone, it was also a none stainless pump. We replaced the pump and engine went back to normal temp.

Using cross overs makes life easier for rigging and servicing the engine but we try to build engines that last.

I am running a crossover with bypass and a thermostat. Without a thermostat temps wouldn't even come off 100 degrees. From my understanding its better to run the bypass for block pressure, and the thermostat to run a constant stable temp. I really cant see there being much difference between a crossover with a bypass and a circ pump as far as water flow. both essentially do the same thing, one uses engine power to circulate water and the other uses water pressure. both once the block fills up and thermostat isn't open dumps the water through a bypass and right out of the exhaust.

Some interesting info here. Seems as if I went the crossover route I would just be making more work for myself, and spending more money. I already have all the original hp500 cooling components so I might as well stick with them.

That would be my thinking, "if it ain't broke don't fix it", but I'm a notorious cheapskate anyway. I would like to see some real world test results showing any actual performance gains from running a crossover. My thinking is that it would be negligible. I think most folks do it for the visual appeal of a cleaner looking engine. If that's your thing and you have the extra coin for it, more power to you. Personally, I don't care so much how pretty my engine is, as long as I get to run my boat all summer with the hatch down instead of up!

I went from a circ. pump to a crossover with a bypass and a 140* thermostat. The only problem I had was too much water pressure in the block. Had to put a pressure relief valve in the line. I also drilled the back of the intake manifold and ran a water line to the front. Seems to work well.

Your thinking is correct. I dyno'd With and Without on this + other things. Squat for difference on 502 up to 5600rpm.

I'm in the North...good luck running without the Merc recirc pump and t-stat up here.....until the water hits 70+F which is only for a few weeks.

It's only my suggestion here and you can take my advice any which way you like but I am absolutely against running without a thermostat! This is why, If you run without a thermostat and your motor does not get to temp it is very likely that you will end up with water condensation in your oil. Correct water and oil temps prevent this from happening. Just something to keep in mind. If you run w/o a t-stat and notice your water temp is low it would be a good idea to install one.