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Thread: Temp issues?

  1. #1

    Temp issues?

    Good evening gentlemen.

    Boat: 2000 tige 21v black scorpion

    A little bit of history. Bought the boat 6 months ago or so. Boat sat for a long time. Lots of initial small issues. Lots of maintenance stuff. Compression checks out. Boat runs great. After replacing water pump, impeller, thermostat was still having temp issues. We narrowed it down to the fuel pump causing the motor to run lean and vapor lock issues. Just replaced the fuel pump assembly. Boat runs better than ever. I mean much better. More responsive, smoother idle, faster, everything. I was topping out in the mid 30’s with top end prop, currently running 40 with bottom end prop.

    After getting it all together (changed fuel pump, service, and changed prop to bottom end prop) we took it to the lake a gave it hell. Ran wide open for extended periods, put it in surf speed/wake and plowed forever. Never ran blower... I pushed it hard. If it wasn’t right I wanted to know then. Two thing came up...

    1. I noticed while running wide open (which I NEVER do) temp would climb after extended time. Not much, maybe 180-190. Not enough to sound an alarm, but it did climb.

    2. I get a “surge” under wide open speeds. Almost like it’s governing the engine. May be normal. I’ve never been able to get the boat to that speed. This doesn’t bother me all that much as again, we don’t run the boat that fast. Just wanted to mention in case it was a symptom.

    Anyone else notice things like this? Normal? Still have a temp issue? Thoughts?

    Thank you,

  2. #2
    Join Date
    Feb 2016
    Boise, ID
    Coupler things to verify I guess...
    Do you know what the rating on the thermostat you out in is? I believe Merc called for a 165* thermostat. Do you have an temp gun? If so I would take temp of manifolds, block, and oil pan and cross check those to gauge to make sure you don't just have a sender or gauge problem.
    If your merc has a low pressure pump that feeds high pressure it could be that HP pump is starving and L.P. isn't feeding it enough fuel causing the surge...
    These are all just wild guesses BTW

  3. #3
    Join Date
    Aug 2010
    Long Beach, CA
    2015 Z3, 1999 2100i
    At what rpm were you running full throttle? The low pressure feed pump freeheel was talking about usually causes a surge of about 500 rpm. If your engine is EFI then the thermostat is a 162* and if you're carbureted its 145. The gauge will usually show 175 for the EFI and 150 for carbs. A climb in temp wouldn't be an eyebrow raise unless it exceeded 190. If you saw steam in the exhaust then you're looking at a minor blockage in the raw water passages of the trans cooler, usually old impeller pieces or weeds.
    Fixing everyone elses boat just so I can use mine...

  4. #4
    Join Date
    Feb 2016
    Boise, ID
    ^^Good call! I forgot how that honeycomb in the transcooler catches stuff.

  5. #5
    How do I go about cleaning out water intake?

    It’s an efi, has proper thermostat (I thought it was 165?) it was the factory replacement. About to grab the boat and work on getting it cleaned up for tomorrow. Would love to flush raw water intake.


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