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  1. #1

    mercruiser 185 4.3 v6 running hot--help!!!

    I'm at my wits end with this motor.....

    It's an '80's model mercruiser 185 4.3 v6 in a searay. Customer brought it to me running hot when trying to run over 3k rpm even after replacing the impeller and removing the t-stat. The first thing we found was the water tube in the gimble housing/transom shield was dry rotted and leaking. replaced the water tube and installed a new143degree t-stat, same problem--runs hot when running over 3krpm. checked the block and manifold drains for sand/rust---nothing. pulled the risers, extremely clean for a boat of this age---it's obviously been a freshwater boat all of its life. checked the power steering heat exchanger, all passages are clean. timing is set at 8degrees.

    The interesting thing is it will boil water over the exhaust cross over in the intake--I noticed this after a quick test removing the t-stat and getting the same over heat problems. the water that got on the intake when I pulled the t-stat housing off would boil when trying to run above 3k rpm.

    Today I shot several spots with my temp gun----the risers are running 140-150degrees. The exhaust manifolds themselves are running 200-210. When I shoot the area above the exhaust crossover in the intake I get readings as high as 260-270 degrees.

    Plugs are almost as white as the day they were made so tonight I'm rebuilding the ole q-jet carb, thinking a lean condition is causing it to run hot----I'm probably still chasing my tail

    compression is 160-170lbs on all 6 cylinders.

    has anyone ran into a similar problem? sorry for the long post, but I'm at my wits end with this one...

    thanks in advance
    Mike Dowling

  2. #2
    Join Date
    Jul 2008
    severn bridge
    check circulation pump.install clear hose on the end of raw water hose and start engine,watch for exhaust blowing into hose stopping water flow.if so you have a crack or gasket problem.

  3. #3
    I would check the heads. I had a problem with overheating on my 27 signature chaparral and it turned out to be the heads where clogged.
    all about the go fast with no tickets

    19 ft nordic pickle fork

  4. #4
    forgot to follow up on this one.....I appreciate the replies. ultimately the running hot problem was due to a warped water pump housing which caused the gasket to blow out.

    now another problem with this one----when I hit the trim it starts skipping. time to check electrical connections. spark appears a little weak on the spark board so maybe it's time for a ignition system tuneup as well.
    Mike Dowling

  5. #5
    Join Date
    Aug 2007
    Ft. Lauderdale, Fl
    Check the battery connections and check all the grounds.
    "One of the penalties for refusing to participate in politics is that you end up being governed by your inferiors". Plato .

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