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2001 V6 2.5L 140HP Mercury running hot

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  • 2001 V6 2.5L 140HP Mercury running hot

    Hi guys,
    I've got a cooling issue that I can't sort. This outboard is what's called a 140hp International i.e. it's an export only model that's common here in New Zealand. Basically it's the same as the 2001 - 2005 150hp to 200hp 2.5L V6 Carb ones you guy are used to.

    It will run hot at part throttle but is fine at the top end. The water pump was replaced but it was still running hot so I replaced both stats. I then had a better tell tail flow and thought the issue was sorted as it was running great initially, but we were running at 4 - 4500rpm.

    At 3000 and lower it gets hot. The gauge will go to 1/2 way between the 3/4 and full marks. Water pressure at 3000 is about 15psi. It has about 3-5 psi at idle.

    I checked the temp sender last night and it seems to be OK. Ranges from about 950 ohms cold (about 64 deg) to about 68 ohms at 212 deg. I put a 5k pot on the gauge to simulate the sender output and I'm now more concerned that I was. During the last outing I pulled the cover and checked the stat housings with an IR temp unit and both showed about 148 but the gauge was well round.

    Simulating the gauge reading I had to have about 40 ohms to get the same reading. This is telling me the head temp was well over 212 deg but the horn remained silent?

    So in short, it runs cool at high speed but heats up quickly at low speed, even 1200rpm. The water pressure looks to be good enough to rule out the pump. Both stats are new and look to be working correctly.
    The motor has only 80 hours on it.

    What else should I be looking at?


  • #2
    Re: 2001 V6 2.5L 140HP Mercury running hot

    I am not familar with that exact model, however, my '93 V6 has a gauge sender and a overheat sensor, one on each head. Perhaps the overheat sensor is bad, or perhaps it was swapped with another temp sensor.

    140* F is what the thermostats open, so if the temp is close to that the motor is cooling OK.

    Have you checked the poppet valve?

    Comment



    • #3
      Re: 2001 V6 2.5L 140HP Mercury running hot

      I haven't checked the poppet valve as it gets hot at low speed just a quickly as it does at 3k rpm and my thinking is the poppet would cause more issues at higher speeds? Correct me if I'm wrong.

      I'm not 100% sure my IR temp gauge is correct but the water coming out of the tell tail was hot but not overly hot. The sensor in the port head is the one I tested.

      The overheat one in the other head could be bad but I'm not sure how to check it as they need to be something like 218 deg to switch (my books not in front of me) and water will only make 212 on a good day.

      The temp sensor in the port head sits in a pocket just under the spark plug and doesn't screw into the head.

      What's the best way to test a poppet?

      Comment



      • #4
        Re: 2001 V6 2.5L 140HP Mercury running hot

        I would think the overheat sensor would short to ground at 180-190*F. It can be tested on the stove in a pot of hot water. I am not sure how to test the poppit, however, you might start by inspecting it.

        Comment



        • #5
          Re: 2001 V6 2.5L 140HP Mercury running hot

          OK I'll pull the overheat switch and test it tonight. The book I have says it changes from N/O to closed at over 212deg which seems to me to be way too late to save the power head from damage???

          What is the typical pressure that a poppet should open?

          Comment



          • #6
            Re: 2001 V6 2.5L 140HP Mercury running hot

            Have you checked to be sure that timing is set correctly?

            Throttle link correct?

            Sometimes an incorrect link between throttle and timing will cause strange heating at part throttle loads yet at WOT timing and throttle are fine and the motor cools perfectly.

            Comment



            • #7
              Re: 2001 V6 2.5L 140HP Mercury running hot

              Monitoring the water pressure gauge at all RPMs is a good way to troubleshoot cooling problems. You described the gauge readings somewhat already, but you might take a closer look at what it does exactly as you change RPMs from idle through WOT. This might also help you evaluate whether the poppets are OK. The below linked guide tells what to look for.

              http://forums.iboats.com/attachment....6&d=1240515681
              1996 Mercury 150HP V6 carbed outboard motor and Maxum 1900XR bowrider boat

              Comment



              • #8
                Re: 2001 V6 2.5L 140HP Mercury running hot

                Thanks for your advice so far. Yes I need to get the boat back on the water and get a good idea of what the pressure is at different revs and how it reacts as the rpm's increase.
                I tested the temp sensor in the starboard head and couldn't get a circuit through it. I had it in water to 212 and then heated it carefully to as much at 240, but nothing. A new one has been ordered.

                The confusing thing is I'm not 100% sure if it is overheating at all!?? The temp gauge indicates it is but the heads and water out the tell tale don't seem overly hot. The temp of the stat housings appears to be about 150 even when is looks to be hot. That's got me stuffed!

                I have roughly checked the timing and all looks good but I'm going to go through that again from the start and verify it is correct.
                Is there a guide to what the timing should be at different revs, not just WOT?

                Comment



                • #9
                  Re: 2001 V6 2.5L 140HP Mercury running hot

                  I guess the timing question's a bit ambiguous (I'm used to thinking automotive) so I'll try a different approach.

                  Is it advanced or retarded timing that's more likely to cause it to run hot at 2k -3k rpm?

                  One more thing... What are the typical parts I'll need if I pull the poppet to check it? Gaskets etc or is there a kit? The Mercury dealer here doesn't know?

                  Comment



                  • #10
                    Re: 2001 V6 2.5L 140HP Mercury running hot

                    Originally posted by McHaggis View Post
                    Thanks for your advice so far. Yes I need to get the boat back on the water and get a good idea of what the pressure is at different revs and how it reacts as the rpm's increase.
                    I tested the temp sensor in the starboard head and couldn't get a circuit through it. I had it in water to 212 and then heated it carefully to as much at 240, but nothing. A new one has been ordered.

                    The confusing thing is I'm not 100% sure if it is overheating at all!?? The temp gauge indicates it is but the heads and water out the tell tale don't seem overly hot. The temp of the stat housings appears to be about 150 even when is looks to be hot. That's got me stuffed!

                    I have roughly checked the timing and all looks good but I'm going to go through that again from the start and verify it is correct.
                    Is there a guide to what the timing should be at different revs, not just WOT?
                    The temp sender is not in the water jacket, but in a pocket in the head. Compare the temp there (with either a thermocouple meter or a known good IR meter) to the temp gauge.

                    The overheat switch trips long after the engine is out of water (temp wise, probably a couple of seconds time wise.) The engine isn't hurt till it gets way up there, so it's in time to save the engine if it goes off because of a weed wrap or pump failure, with the caveat that you have to hear the alarm and shut down.

                    If you have a strong tell-tale, it's getting enough water to fill the water jacket. If the tell-tale isn't scalding hot, (as in first degree burns in 1 second) it's not overheating.

                    Like someone said, if you can give us pressure gauge readings through the rpm range, it'll help discern if there's a problem and what it might be.

                    hope it helps
                    john

                    Comment



                    • #11
                      Re: 2001 V6 2.5L 140HP Mercury running hot

                      Originally posted by McHaggis View Post
                      I guess the timing question's a bit ambiguous (I'm used to thinking automotive) so I'll try a different approach.

                      Is it advanced or retarded timing that's more likely to cause it to run hot at 2k -3k rpm?

                      One more thing... What are the typical parts I'll need if I pull the poppet to check it? Gaskets etc or is there a kit? The Mercury dealer here doesn't know?
                      You need two gaskets to open up the poppet and know you'll get it back together. Once in, the most likely parts needed would be the rubber seat, and the diaphragm. Once you've opened it up and cleaned up all the gasket surfaces, and maybe used a little grease on the gaskets, you should be able to pop it open to look for a jam of debris with no parts.

                      The linkage setting that would most likely affect this is throttle pickup timing. If it picks up too late, you could be running lean at that point.

                      hope it helps
                      John

                      Comment



                      • #12
                        Re: 2001 V6 2.5L 140HP Mercury running hot

                        Originally posted by j_martin View Post
                        The temp sender is not in the water jacket, but in a pocket in the head. Compare the temp there (with either a thermocouple meter or a known good IR meter) to the temp gauge.
                        New parts have arrived.
                        Is there a way to bench test this sensor before it's installed in the head?

                        Also I'm replacing the Port head 2 wire sensor that drives the temp gauge. The original one seems to have some stuff on it and its looks a bit like silicone grease. I guess I should install the new one with the same? What's it likely to be?

                        Comment



                        • #13
                          Re: 2001 V6 2.5L 140HP Mercury running hot

                          Heat transfer paste. Used to ensure a good thermal connection and to reduce possible oxidation (oxidation tends to insulate the sensor, that's no good).

                          Auto parts stores list its use for seating the module in GM HEI distributors.

                          Computer shops use it to bed the processor to the heat sink.

                          Comment



                          • #14
                            Re: 2001 V6 2.5L 140HP Mercury running hot

                            Check out my post on high temps at low RPM. My main problem was that the impeller was installed backwards.

                            http://forums.iboats.com/showthread.php?t=450986

                            Comment



                            • #15
                              Re: 2001 V6 2.5L 140HP Mercury running hot

                              New temp sensor installed and rechecked the temp switch. It wasn't switching initially but is now so it went back in.

                              Checked the timing and throttle link as suggested by CharlieB and it wasn't that good. The pointer was dead on the .462 mark and it cranked at 26 BTDC but there was quite a bit of slack between the throttle cam and roller letting the timing advance well ahead of any throttle movement. I turned the link rod out about 4 full turns to remove the play and reset the idle stop and WOT screws to spec. Its at about 9 ATDC at idle.

                              Have yet to get back on the water as it's been windy for days but looks to improve mid week so will post back after that.

                              Question: The trigger rod setting says it should be 11/16" long from where the threads protrude out of the locknut to the 90 deg bend. Where on this bend? The middle or the overall length? How important is this if the timing checks out otherwise?

                              Comment

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