The cooler your using was put on an engine making 415 hp, your almost double that, what size lines are you running, the cooler that I posted a picture of is expandable and I think will support up to 1000hp but you would have to call and ask them, good luck

Round tube style 3x21 Max 650hp 3x25 max 1000hp after that I guess you need 2

These were on my old engines 600 hp, no matter how hard I ran boat temps never went over 230 ever...... These are 3x18"

I now have 3x18" mr cools and he told me will support 700 hp all day long.

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Mr. cool actually goes by the bundle size. Your 3x18 coolers = everyone elses 3x21. I have a 3x25 and it's about 30" if I remember correctly.