High temperture reading

Discussion in 'General Maintenance/Repair Questions' started by Loyd Dinneen, Aug 13, 2018.

  1. Loyd Dinneen

    Loyd Dinneen Active Member

    425
    Jul 29, 2017
    Las Vegas
    1977 Sea ray 240 SDA cruiser w/ twin 470 mercs.
    Twin 470 Mercruisers
    I have twin 470s and they show that they are running hot on the gauge but measured with a lazer shows running at 160 or less at the reservior and all points on the engine. Have changed out the thermostat and the temp sender and now it reads even higher on the gauge on the port engine, have yet to change sender on stbd side. Gauge pegs when grounded like it should on port havent checked the stbd side. Thinking that either the gauge is bad as they set halfway when switch is off or I have the wrong senders. Again temps look fine at all the points to measure(exhaust elbow,reservior, heat exchanger, all hoses, block, and head,)and waterpump is new on both engines. Has anyone ever ran into this problem before?. The boat is a 1977 240 SDA Srv Sundancer with twin 470s that run perfect except for this, any help would be appreciated.
     
  2. CliffA

    CliffA Well-Known Member GOLD Sponsor

    Dec 29, 2009
    Lake Norman, NC
    2001 Sea Ray 340DA
    Name: 'Happy Place'
    4.5kW West. Generator
    Purchased Nov. 2014
    Fresh Water Use
    Twin Merc. 6.2L (MPI)
    640 hp (Total)
    Raw Water Cooled
    V-Drive Transmissions
    every temp gauge I have seen on a boat will return to '0' once the engine cools.....if your needle is sticking at the 1/2 point on the gauge I would suspect a problem with the gauge....

    good luck...

    cliff
     
  3. Loyd Dinneen

    Loyd Dinneen Active Member

    425
    Jul 29, 2017
    Las Vegas
    1977 Sea ray 240 SDA cruiser w/ twin 470 mercs.
    Twin 470 Mercruisers
    Well I put the old sender back in and refilled the system with distilled water and antifreeze at a 50/50 mix and fired the port side up and it looks like the problem was old antifreeze and needing a flushout. The exhaust elbow is running nice and cool at 110 and gauge showing half up and engine lazored at below 160. I then fired up stbd engine and gauge at half up and lazored at about 154 at the tank and 133 at the exhaust elbow and it feels alot hotter than the port side. I suspect that there maybe a restriction there and causing the engine to run warm. The temp of the tank below the reservior is running 170 midway down. Could this be a problem with the flapper thats I believe is located in the exhaust elbow?
     
  4. Loyd Dinneen

    Loyd Dinneen Active Member

    425
    Jul 29, 2017
    Las Vegas
    1977 Sea ray 240 SDA cruiser w/ twin 470 mercs.
    Twin 470 Mercruisers
    Took off the exhaust riser and turns out that the neck was cracked and there was some corrosion in the slots. Exhaust was nice an sooted up. The 3x4 bellows hose was burned at the neck so it was running hot. So I ordered another elbow, gaskets, and bellow. One of the ports was completely plug even though antifreeze doesn't run thru it as it is blocked by a metal plate, only clear water came out so I believe that the elbow is blocked partially internally where the fresh water runs. Anyway parts are on the way and hopefully the overheating fix. There are no flappers and I believe now that the gauges are reading fine.
     

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