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2015 T50LB Overheating - Unable to identify route cause

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  • 2015 T50LB Overheating - Unable to identify route cause

    Hi everyone. I'm new to this forum but have read countless posts by others trying to diagnose and resolve my overheating issue. There appears to be a wealth of knowledge here and I'm hoping that knowledge can help me out of this situation and back on the water.

    I recently bought a pre-owned, 2001 Caribe (14' RIB) which has been repowered with a 2015 Yamaha T50 LB. When I tested it before purchasing it ran on the hose flawlessly for quite some time. My first time taking it out (and every time thereafter) I have faced overheating and low oil pressure alarms. I believe the low oil pressure is the result of the oil getting too hot, but wanted to share this detail in the event is alters someone's approach when thinking about potential causes for this issue. What's strange is that the motor performs well at cruising speeds but when I throttle down for a No Wake zone or to put it back on the trailer, the alarm horn IMMEDIATELY sounds and the high temp or low oil pressure lights illuminate on the tach (old analog tach).

    In the interest of responsible boat maintenance and to resolve what I'd think would be 95% or more of the issues, I replaced the engine oil (Yamalube 10W-30) and filter, lower unit oil, spark plugs, water pump (impeller, cup, gaskets, woodruff key, O-ring, but not the housing), and for good measure the thermostat. The problem persisted. From reading other posts here, i thought there might be a blockage in the cooling lines, water jacket or exhaust cover. I was really hoping that it was the pencil anode breaking and blocking flow, as tony_dix experienced, but the anode was intact. With the exhaust, cover removed i took the opportunity to blow compressed air and jets of water through the cooling pathways to try to free any blockages caused by corrosion or foreign object. The water jet seemed to work, especially when I covered some of the other outlets leading to the cylinders to focus flow to the others. I'll note that through the use of an IR thermometer I've identified the source of the hot spot as Cylinder #1, so that cooling channel was my primary focus. I also identified a blockage in one of the water passages for the fuel cooler and was able to clear it.

    I've tried to isolate and troubleshoot every aspect of the cooling system I can think of, but haven't been able to resolve the overheating issue. My best guess is that at low RPM insufficient water is being circulated to adequately cool the motor. I've also been running it with the thermostat removed. This provides marginal improvement but hasn't resolved the issue. I also thought that Cylinder #1's injector could be partially blocked causing it to run lean (and hot), and the hot spot couldn't be cooled with low-RPM water flow rates. I swapped two of the injectors but the problem persists.

    I've found only one thing that keeps it from overheating, but it's not a viable solution for operation on the water... When I operate the motor on the hose (ear muffs) with the thermostat removed (haven't tried this with it installed) AND have a second hose attached to the factory flush device the motor doesn't overheat. As a data point, when operating with ear muffs only, very little cooling water exits the exhaust via the prop, but substantial volumes are discharged here with both hoses attached.

    Lastly, I discovered that the tell-tale was robbing what little water pressure I have at idle. When I covered the tell-tale with my finger the motor cooled itself more efficiently. This may be an unpopular practice but I removed the tell-tale from the cooling loop and it has helped, but I realize this is a band-aid on stab wound and not a perfect solution.

    I've attempted to list and describe everything I've tried, but I'm sure there's more I've tried and don't readily recall. I've been working on this with every free moment I have for the past month or so. Any help that someone more experienced than I can offer would be greatly appreciated.

    Garrett
    Last edited by garrett.weeks; 1 week ago.

  • #2
    if that little flow out of the Tell tale makes a difference, I would be looking hard for why the pump is not pumping enough water up into the block.
    you said you did not replace the housing, and you did not mention the wear plate, so I would try those and make sure the seals on the water tube are in place properly.

    also low oil pressure would worry me, so measuring that would be a good idea
    or at least make sure the switch operates in specs

    Comment


    • #3
      make sure that the water seal in the water pump hsg is in place, if the water pump hsg has ever been replaced then maybe that seal was not refitted, this seal does not come with new hsg & is located under the water tube guide that clips into place on the hsg, the part number for this seal is 663-44366-00 if you need to view on Boats.net net website as to where it is located, i have seen where this was omitted when the hsg had been replaced & this omission can/will cause low water pressure at idle, but fine at high speed.

      Comment


      • #4
        Thank you very much for the response. I did replace the wear plate but forgot to mention that. I've ordered a new housing and damper water seal (for inside the housing) just to rule those out as the potential cause, or potentially resolve the issue. I'm most intrigued by your suggestion of the seals on the water tube. I agree the issue seems indicative of inadequate water flow through the cooling system. I have a couple of ignorant questions:
        1. Are the water tube seals the only thing holding it in place? i.e., can i just pull it down/out with the lower unit removed?
        2. Should water come out of the hole in the water pump housing for the prop shaft? I suspect some is fine, or even necessary, but how much is too much, and could this be robbing my water pressure? With the lower unit removed and ear muffs attached, water shoots up the prop shaft hole through clearance around the prop shaft.
        Is the seal that goes in the housing and the one identified in the image below the two seals i should inspect for proper placement and fitment?
        Water Tube Seal.png

        As for the low oil pressure, to-date i chalked it up to the oil getting overheated, making it too thin to establish adequate pressure. I connected an oil pressure gauge and inspected it during a low oil pressure alarm (resulting from slowing from cruising speed to idle). There was essentially zero oil pressure so I shut down the engine immediately. I also pulled this dipstick and found just a couple of small bubbles, but I wouldn't necessarily say the oil was foamy. I have not checked the oil pressure from a cold start but will do so and monitor as the engine warms, and report back.

        I took it out yesterday and much to my surprise it didn't overheat, but I did experience a low oil pressure alarm. After shutting it down for 2 minutes i was able to restart and return to the ramp without issue. I flushed the engine on the hose when I got home and it overheated... I can't win.

        Comment


        • #5
          Originally posted by Tony Harper View Post
          make sure that the water seal in the water pump hsg is in place, if the water pump hsg has ever been replaced then maybe that seal was not refitted, this seal does not come with new hsg & is located under the water tube guide that clips into place on the hsg, the part number for this seal is 663-44366-00 if you need to view on Boats.net net website as to where it is located, i have seen where this was omitted when the hsg had been replaced & this omission can/will cause low water pressure at idle, but fine at high speed.
          Tony Harper , thanks for the part #, that's the one I have on order but it won't arrive until Monday. I'm a little confused when looking at the exploded view of Lower Casing Drive 1 and Lower Casing Drive 2. They seem to disagree as to which seal goes into the housing... #1 (right side of the image below) suggests that part# 663-44366-00-00 (Damper, Water Seal 2) goes in the housing while Lower Casing Drive #2 (left) suggests part# 663-44367-00-00 (Damper, Water Seal 3). Is there a mistake here or are both required? thanks!

          Comment


          • #6
            Originally posted by garrett.weeks View Post

            Tony Harper , thanks for the part #, that's the one I have on order but it won't arrive until Monday. I'm a little confused when looking at the exploded view of Lower Casing Drive 1 and Lower Casing Drive 2. They seem to disagree as to which seal goes into the housing... #1 (right side of the image below) suggests that part# 663-44366-00-00 (Damper, Water Seal 2) goes in the housing while Lower Casing Drive #2 (left) suggests part# 663-44367-00-00 (Damper, Water Seal 3). Is there a mistake here or are both required? thanks!

            yep, just had a look at my parts break down & what you have mentioned is def shown on those parts break downs,

            from what I can tell is that maybe there is a fault in the spare parts break down images,
            because 663-44366 suits the smaller hub gearbox with the 6H3-44311 hsg & 6H3-44352 impellor

            where as the 663-44367 suits the bigger hub gearbox that uses the 688-44311 hsg & 688-44352 imp,

            I am not sure which gearbox you have, but that will determine which damper is correct for you, quick easy check is what part number impellor is correct for you engine

            Comment


            • #7
              Originally posted by Tony Harper View Post

              yep, just had a look at my parts break down & what you have mentioned is def shown on those parts break downs,

              from what I can tell is that maybe there is a fault in the spare parts break down images,
              because 663-44366 suits the smaller hub gearbox with the 6H3-44311 hsg & 6H3-44352 impellor

              where as the 663-44367 suits the bigger hub gearbox that uses the 688-44311 hsg & 688-44352 imp,

              I am not sure which gearbox you have, but that will determine which damper is correct for you, quick easy check is what part number impellor is correct for you engine
              Thank you, that's a helpful clarification. Mine is the smaller hub gearbox. The seal in the housing is installed, but i will replace it with a fresh one once received. The lower water tube seal appears to be in place and in reasonable shape (picture below). Do you just pull the water tube out from the bottom to inspect the top seal? If it wasn't already obvious I'm trying to rule out everything I can before I'm forced to pull the head and don't want to go yanking the water tube out the bottom if that's going to cause me headache down the road trying to reinstall. It appears to be in there tight.
              Yamaha T50 - water tube (lower seal).jpg

              Comment


              • #8
                Originally posted by 99yam40 View Post
                if that little flow out of the Tell tale makes a difference, I would be looking hard for why the pump is not pumping enough water up into the block.
                you said you did not replace the housing, and you did not mention the wear plate, so I would try those and make sure the seals on the water tube are in place properly.

                also low oil pressure would worry me, so measuring that would be a good idea
                or at least make sure the switch operates in specs
                Checked the oil pressure from a cold start. It started around 30 psi and in less than a minute began to hover around 10-15 psi. Ultimately, it settled around 10 psi at idle. The oil pressure increases when RPMs are increased. Oil pressure was +/- 50 psi at 2200 RPM.

                I also performed a compression test with the engine warm. All cylinders ranged from 95-105 psi. I believe the spec for minimum compression on this engine is 116 psi. Am I looking at a failed or failing head gasket or likely something more? I found it interesting that while low they were all within +/- 10% as intended. Overheating, low oil pressure, and low compression - any thoughts or suggestions would be appreciated.

                Comment


                • #9
                  Originally posted by garrett.weeks View Post

                  Thank you, that's a helpful clarification. Mine is the smaller hub gearbox. The seal in the housing is installed, but i will replace it with a fresh one once received. The lower water tube seal appears to be in place and in reasonable shape (picture below). Do you just pull the water tube out from the bottom to inspect the top seal? If it wasn't already obvious I'm trying to rule out everything I can before I'm forced to pull the head and don't want to go yanking the water tube out the bottom if that's going to cause me headache down the road trying to reinstall. It appears to be in there tight.
                  Yamaha T50 - water tube (lower seal).jpg
                  i would leave that in place in the trunk, I have never taken it out that way, from memory it is not designed/installed to removed that way

                  Comment


                  • #10
                    Originally posted by garrett.weeks View Post

                    Checked the oil pressure from a cold start. It started around 30 psi and in less than a minute began to hover around 10-15 psi. Ultimately, it settled around 10 psi at idle. The oil pressure increases when RPMs are increased. Oil pressure was +/- 50 psi at 2200 RPM.

                    .


                    For my F150, I suspect your oil pressure would/should be close to this:



                    Capture.JPG
                    Attached Files
                    Scott
                    1997 Angler 204, Center Console powered by a 2006 Yamaha F150TXR

                    Comment


                    • #11
                      I would expect a 4 stroke motor to have more compression than a 2 stroke and 100psi is low on even a 2 stroke.
                      and low oil pressure.
                      that sucks big time

                      Comment


                      • #12
                        How were these pressures measured? Hopefully not Harbor Freight tools....

                        Comment


                        • #13
                          Originally posted by pstephens46 View Post
                          How were these pressures measured? Hopefully not Harbor Freight tools....
                          Ha! Fair question. Not Harbor Freight but still trash from the People’s Republic.

                          After running a borescope through each of the cylinders and seeing the condition of the piston heads, exhaust valve, etc., I broke down and took it to a marine mechanic. I didn’t want to go through the hassle of pulling the head to replace the head gasket only to learn that wasn’t the primary (or only) issue.

                          thank you all for your help and suggestions.

                          Comment

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