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Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I bought a brand new (2015 or 2016) Mercury 155 HP motor

Customer Question

I bought a brand new (2015 or 2016) Mercury 155 HP motor last year along with a Lund Crossover boat. The motor was fine during the first summer. However, this year, when going at full speed with the motor properly trimmed I cannot trim it back (lower it) to allow for a temporary speed reduction (25 mph) followed by a return to my regular cruising speed (40 mph). Pushing the trim switch will simply not do anything. The only way I can trim it down is to reduce the speed to 0 mph (or close), put the motor in neutral, lower the motor, then accelerate... This is rather annoying, since one of the manoeuvre where this is necessary is to pass a boat going at lower speed, when you want to temporarily reduce the speed to jump the wave, then quickly accelerate; you kind of look stupid, having to stop your boat to do so!
Submitted: 10 months ago.
Category: Boat
Expert:  Jason replied 10 months ago.

Hi Eric my name is Jason.

I read what you wrote. Do this for me as a test. Start with the engine off. Push the throttle all the at forward as if you were going full speed. Will the trim buttons on the shifter handle work, or are they dead?

Customer: replied 10 months ago.
Hi Jason,Sorry for my late reply, I was at my workplace when I received your reply... and my boat is in my backyard... I am an electrical engineer, so you can ask me questions you would not dare to ask to "regular people"...Anyway, I tried what you suggested and a bit more, namely:1) Rear Tilt/Trim switch (on the motor case) motor stopped, works up & down, no problems;
2) Front Tilt/Trim switch (on the shifting handle) motor stopped, works up & down, no problems: neutral, half way forward, full forward.I tried a couple of times each, so no appearance of intermittent problem (anyway, the issue I describe is very consistent: it happens all the time!As I said, the issue seems to reside in the trimming section of the motor up & down course: it goes up and down (for the tilt part) but stop going down (for the trim part) when going forward... I read a bit on the subject, and the mechanism seems to be pretty straightforward: a motor, solenoids, and a pump. Nobody talks about the Tilt & Trim as being different. For me, it appears to be from the behaviour of the motor and from the fact that there is a Tilt/Trim dial on the dashboard where the needle indicating the motor position initially (when the motor is going up from its lowest position) appears to move slowly (I deduct the motor is trimming), then about a quarter up appears to move faster (I deduct the motor is tilting). The specs also talk about a -4 - +16 degrees trimming range I believe. Obviously, when the motor is fully up, it sits at more than 16 degrees.Also, what seems strange is that the motor going forward should push the motor down. Therefore, if I am trying to lower it, it should be easier for the actuator (motor & pump) to do as opposed to moving it up. So if there is a leak somewhere, I should have more trouble moving it up than down, but it is the reverse?The only thing I remember that could have changed the Tilt & Trim functionality as compared to last year is that I remember hitting a rock at low speed. I don't remember if it was before or after this issue appeared. The feet of the motor hardly has any sign of this hit - maybe a small scratch -, but perhaps it may have affected the Tilt & Trim functionality... Again, having had this happened to me on another motor (Yamaha), the motor would not keep its full tilted position over a day (i.e., the pump seals were broken), which does not seem to be the case here. Well I left it up this evening with no support, so I will see how it behaves tomorrow!
Customer: replied 10 months ago.
Oh yes, as I said, my boat is in my backyard, so there is a limited amount of testing I can do until Saturday when I can bring it to the water and perform additional "live tests"... So for now, I have to rely on my memory of what was happening this summer when I was out on the lake...
Expert:  Jason replied 10 months ago.

Hi Eric,

The only time I've ever heard of a scenario similar to yours is if there is a short circuit inside of the shifter handle, and that's why I wanted you to push it forward. At this point i'm not sure what to say so lets see what happens when you put the boat back in the water.

Customer: replied 10 months ago.
OK I hear what you say...If I recall my hydraulic circuit course, usually there is an actuator valve and a check (free-flow) spring loaded valve in parallel on both sides of the piston (actuator). If any of those are broken, then I think I could have an issue similar to mine... For example, if the check valve does not open, then regardless of whether you open the opposite actuator valve or not, the fluid will not flow that therefore the motor will not rise (or lower).I don't know if this Tilt & Trim circuit is built the same way, but I suspect it is...The thing that is strange is that this issue seems to be "pressure sensitive"; everything works fine when the motor does not push the boat but when it does, there is some extra internal pressure in the piston (fluid) that prevents one of those valve functioning properly... So which valve could be "pressure sensitive"? I suspect the check valve one... For some reason, it is able to open when there is not too much pressure and it is not when there is more pressure... Looks strange to me?On the opposite, if it is the actuator valve, it is surprising that it would be designed to be pressure sensitive; after all this valve has to withstand the enormous pressure that builds up into the piston when the motor pushes the boat (there is 115 HP of thrust pushing it). So again if this valve works fine when there is minimal pressure, it should work too when there is more?Anyway, I will put the boat on the water Saturday and try to understand better what happens. If you have any ideas of what I could try, don't hesitate to forward those to me!I will keep in mind what you said about the short circuit to see if this could cause the problem...Thanks and have a good day!
Expert:  Jason replied 10 months ago.

Whatever the issue is, this should be under warranty. Have you had it into the dealer yet?

Customer: replied 10 months ago.
Oh and I think that I remember that you can hear the Trim & Tilt motor working when this issue manifests itself but simply nothing happens, the motor does not lower... So it has to be somewhere in the hydraulic circuit: either the actuator valve does not open (and this may be for electrical reasons) or the check valve...I cannot recall for sure if I can raise the motor at this time (when I cannot lower it), but I think I can...
Customer: replied 10 months ago.
No that is the next step... I just wanted to know more about the issue before I do in case they say I have to pay for it... While researching this, I saw quite frightening comments on the internet about how Mercury handles its customers having issues with its products. Granted that given the number of motors they produce, there is bound to have unhappy customers, but nevertheless, I would prefer not to be in that group...Actually, when I bought my boat, I would have preferred to have a Yamaha motor, but Lund boats were only fitted with Mercury (I think nowadays, they are both owned by Brunswick and going to the Mercury side, they openly compare their motors to Yamaha motors)... Given that, I purchased a quite expensive "additional warranty" to protect me in case I made a mistake in my purchase, but still... Granted that nothing is perfect, and even I was pretty satisfied with my 40 HP Yamaha, it still blew on me on a lake, so... The only "constant" I saw on the net about Mercury is their Verado line which seems to be pretty flaky. Fortunately, I don't have one!
Customer: replied 10 months ago.
OK tried it again this morning... The symptoms of the problem are very close to what I described except for the following: when the issue manifests itself, not only does the motor doesn't go down, it doesn't go up either. Indeed, when I try to tilt it up, it shakes up & down, but doesn't move at all. In fact, it appears blocked in position by some mechanism that only unlocks itself by putting the speed lever in the neutral position...The issue does not manifests itself unless I trim the motor (probably) past the superior limit of the trim range... If I trim the motor at high speed (to find the best trim position to attain the fastest speed) but stay within the trim range, then everything is fine. If I trim it up a little bit further, then I have the issue (the Trim & Tilt functionality is gone and the motor is locked into its position, until I return to neutral)... I say probably past the superior limit of the trim range because I have a trim indicator on the front panel and I think I can approximately see where it occurs (when the needle is about a quater up from the bottom position)...I brought the boat back to the place I bought it afterwards to winterize it and asked the service people to call me when they work on it next week... One of the owner told me that the problem is probably a broken relay somewhere in the Tilt & Trim circuit... a minor fix apparently.

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