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Water temp goes down at wot and up at idel ?

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Old 07-09-2002, 01:00 AM
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Default Water temp goes down at wot and up at idel ?

My friends 38 fountain with 502's and 250 B&M blowers with single 1050 holleys , EMI exhaust, has this problem . He was running cross over with no thermostat but had little to no temp readings and he got nervous . He put in thermostats and drilled holes in them . Now at idel it runs 145 degrees and running hard it never goes past 120 . I think that is strange to have more temp with no load . Oil is normal ,runs 230-240 at WOT . Any thoughts ......
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Old 07-09-2002, 06:52 AM
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Just some thoughts: It would nice to know what the water pressure is, one thing is while under way and at speed (depending on the type of water pick-up) there is more water flow and pressure being pushed through the motor therefore it could lower the water temp.

When at idle the raw water pump may not be puting out enough pressure and causing the temp to rise. Check / change the impeller.
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Old 07-09-2002, 08:18 AM
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Yep, ck the impeller
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Old 07-09-2002, 02:32 PM
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Good thinkin !! No wonder why you guys are the pros ! Thanks !
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Old 07-09-2002, 04:04 PM
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need a impellar
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Old 07-09-2002, 04:25 PM
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My motors do the same, even with freshly installed impellers and pump housings. Idle is 130-140 degrees, drops about 10 degrees once on plane. At cruise it comes up again to 130-140. On plane the water pickups get a lot of ram flow which pumps more water than just the pumps running suction.

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Old 07-09-2002, 04:46 PM
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145* is not hot for a motor of that nature. The lack of a curculating pump may be the reason. Also when the boat is on plane the water is being forced through the system at a higher pressure.
Ck the impella to be sure, but I believe your freinds experience is normal without that second pump. Most 8 cyl. motors today run at much hotter temps than 140*, 180-200*.
FYI, ran aground one day and destroyed both impella pumps in the sandy bottom. Just for ****s and grins took the already getting ready to overheat motors and put them on plane, as long as I stayed fast and on top, the temps came down to 140* and allowed us to run home fast instead of a tow boat. All due to the low water pick up on the front of the bravo drive.
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