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1990 GT150 Overheating, What else should I look at?

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  • 1990 GT150 Overheating, What else should I look at?

    Good Afternoon, I've used the forum resources to research lots lately and can't figure out which direction to go. As the title states, I'm having overheating issues with a GT150. I took it out recently, idled for a while as I parked the trailer, got out past the no wake zone and opened her up to 3500-3800rpms. Within 2 minutes the overheat alarm went off. Let it cool down and limped it towards the ramp. No alarm till I opened it up again and within a minute it sounded. The telltale was a steady stream of ice cold water. It appears that at idle its ok. So I pulled the heads off and the water diverters were badly deformed and pushed through where they should be. Changed all 6 of those diverters and changed the thermostats and bypass valves below the thermostats for good measure. The only thing I didn't change was the rubber grommet that the bypass valves sit into because I wasn't sure at the time how to remove the old one. Took the boat out again and same thing, idles fine, overheats when I get the rpm's up. I haven't tested the exact temperatures of the heads yet because I didn't have my temp gun with me but its extremely hot to the touch so I don't think my sensors are bad. The water pump was changed this past summer and it was running fine all summer with no issues so that was installed properly and is only 8 months old. My question is where should I check now? Ive tried reading online and can't come up with any other items to check. I pulled the new thermostats out just to double check and they are working correctly in a cup of boiling water. I just ordered new gaskets for the water jacket cover so I can change the little grommets that I skipped before but I'm out of ideas and getting very frustrated. Water flows through the tell tale steady but is always ice cold. I normally run in fresh water and not shallow. No sand or mud issues that I've noticed but I flushed through different ports with air and the hose just to make sure. Yesterday as I was playing with it on the earmuffs, after putting the heads back on, making sure the diverters were still in place, I started it and the telltale started getting warm, hot and then right back to ice cold for the rest of the day of starting and stopping the motor. Unfortunately I can't replicate the overheating unless its under load but I'm hoping that maybe the scenario of the water getting hot then turning ice cold will spark an idea? At home at idle, the heads were right in the 140 mark like they should be. Please help...

  • #2
    Welcome to Iboats,

    Is this a first hand or second one engine used in salt water by previous owner ?

    Happy Boating


    Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

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    • #3
      Id pull the LU off to check that newish impeller. Perhaps a fin has come off and blocked some part of the system.
      So long as the bypass valves look ok and move alright in position by hand i always give them a pass mark

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      • #4
        welcome aboard.

        always start at the impeller.

        hitting a piece of seaweed or a plastic bag is all it takes to starve the impeller and melt it.
        Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

        1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

        Past Boats
        1970 Wooster Hellion - Merc 9.8
        2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
        1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

        What’s behind you doesn’t matter.Enzo Ferrari

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        • #5
          Thanks for the responses so far. As far as ownership, this has been through a few owners, but I've owned for the last 4-5 years now. I live in SC, 2 miles to the ocean, 3 miles to the Intercostal Waterway. I know the previous owner only used on the waterway in fresh water, I use it about 75% in fresh as well. From pulling the heads, there was a small amount of salt, but not much at all. I guess I will pull the LU this weekend and see how the pump looks. The stream doesn't seem to have weakened at all since installation but thats just using my eyes. I pulled the water jacket covers today and replaced that bushing I mentioned. The old ones were a tight fit around the bypass valve and had formed into the shape of the plastic valve whereas the new one doesn't even touch it really and is perfectly round. I still don't think that was holding the valve from opening but I'm trying to rule anything out at this point. The gaskets were pretty rough, very soft and flexible almost like wet cardboard. Unfortunately I just ordered the new ones today online so I won't even be able to water test anything till they come. In the mean time I will pull the lower over the weekend and see how that looks. Thanks

          Comment


          • #6
            Is the water jacket cover same as the exhaust cover ? With older engines that have passed through many owners boating in salt and fresh water sometimes it's better to pull whatever part with a gasket to inspect their internal condition, check how much salt build up, oxidation has been going on there if any. Will have a better idea about the overall internal powerhead condition of the engine and go from there with simple DIY maintenance procedures.

            Happy Boating


            Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

            Comment


            • #7
              The water jacket cover is on top of the head. Its a thin cover with lots of bolts that just exposes the other side of the internals of the heads. I could be calling it by a wrong name. But funny you mention the exhaust cover. I pulled my lower and the entire water pump is melted! The cover has bits of hard melted plastic and the fins are all melted too. I will add some pictures. I have never dry started this engine and the pump is less than a year old, I almost always start at the boat ramp and occasionally on earmuffs. Every time I start it, the telltale starts peeing water almost immediately. My thoughts are that the exhaust gasket is leaking heat directly onto the pump housing? The exhaust gasket is intact but slightly distorted. The few times it alarmed that it was overheating, I immediately shut off and dropped anchor to wait till it was cool. Am I on the right track? Have you guys seen this before?

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              • #8

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                • #9
                  No doubt about it , that pump ran dry.-----From here without more information / history I can not say why / how it ran dry.-------Plastic bag in the water ??

                  Comment


                  • #10
                    Thats dry run...either muffs came off when testing,not deep enough on barrel/tub or debris wrapped around water intakes. Install a complete repair kit, housing and all.
                    When in doubt,Trim it out!!!
                    Business Owner & Certifed Technician
                    Boats I own & use
                    20ft Javlin w/250 Junkrude
                    17ft Bullet w/200 Merc (SOLD!!)
                    13ft Allison w/150 I-6
                    17ft Hydra-Sport 175GT
                    15ft Allison w/75 Stinger(project)
                    14 x 48 Drifter with 1100SS Merc

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                    • #11
                      Have seen worse cases, no impeller whatsoever was found completely melted, just the drive shaft key inside liner. Seems you have waited to long to check that water pump condition while experiencing repetitive engine overheats. Next time don't bypass the WP.

                      Happy Boating


                      Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

                      Comment


                      • #12
                        Sign up today
                        Thanks everyone, I have all parts on order for the water pump as well as for the exhaust gaskets.

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