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Old 29-07-2018, 19:04   #1
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Tohatsu Outboard check oil light coming on

I have a new(ish) Tohatsu 6hp 4-stroke that has been having the check engine (oil pressure light) come on, only at idle throttle after running the engine at 1/2 throttle load or higher. It was bought at auction from a business closing down, and was a floor model, so yeah probably dumb move on my part in retrospect, but it was a new outboard for $900.

Like I said the check oil light comes on at idle, but the oil level is correct and I recently changed it, with Sierra 4-stroke 10-30 which meets spec. Usually the oil pressure light comes on when throttled down to idle after running for 10-15 minutes at load, but no other issues are exhibited most of the time. Occasionally, about 1 in 20 runs, the engine starts losing power in brief spurts - like the rpm is dropping for a second or two or almost like it's going into neutral and back into forward. Other than this 5% occurrence, it runs well, sounds good, cooling water is always flowing, and it's not smoking or showing other red flags.

Fuel is fresh and has fuel stabilizer. I've also changed the spark plug (properly measuring the gap) just for the heck of it, changed the fuel filter, and cleaned the carb, which looked nearly sparkling clean.

Are there any resources I can find on how to diagnose outboards? I read a couple books but they were pretty basic and the ones more than 10 years old talk about 4-strokes as pretty new technology (because they were), which they don't go into much depth on.

Does it sound self-serviceable? Outboard mechanics charge $190/hr in the Seattle area and they said min 2 hours to do anything, so it could be nearly half the cost of the engine to fix a mostly new engine. So I'd like to do it myself if possible, and I'm not really sure I have a problem big enough that it's worth spending $400-500 on.
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Old 29-07-2018, 19:43   #2
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Re: Tohatsu Outboard check oil light coming on

You certain it's an oil PSI ight?
My Suzuki has a check engine light, and when it's new the light will come on to tell you to change the oil, and later I assume if the engine has sensor issues, just like a car
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Old 29-07-2018, 20:22   #3
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Re: Tohatsu Outboard check oil light coming on

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You certain it's an oil PSI ight?
My Suzuki has a check engine light, and when it's new the light will come on to tell you to change the oil, and later I assume if the engine has sensor issues, just like a car
Interesting idea, but as far as I can tell, reading from the manual, the Tohatsu 6 4-stroke warning lamp only comes on to indicate engine speed over max rpm (in which case the electronic safety governor would also be on limiting rpm), or to indicate low oil pressure.

I've emailed Tohatsu a couple times and they said it's designed to turn on with low oil psi, and that it could be an oil psi issue, cdi, or wire harness. CDI or wire harness doesn't sound user serviceable to me.

We're currently cruising for 6 months, near Nanaimo BC now. So it's hard to take it to a dealer because we're generally only in a marina for <24 hours, once every 10 days or so (and most outboard centers want you to drive the outboard to them with a car).
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Old 01-04-2020, 15:27   #4
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Re: Tohatsu Outboard check oil light coming on

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Usually the oil pressure light comes on when throttled down to idle after running for 10-15 minutes at load, but no other issues are exhibited most of the time. Occasionally, about 1 in 20 runs, the engine starts losing power in brief spurts - like the rpm is dropping for a second or two or almost like it's going into neutral and back into forward.
This slowing down of the engine is the low speed electronic governor working to protect the engine. It keeps the engine from running at greater than 2300 rpm or so. The low speed EGS comes into play when oil pressure is low. Ideally you would stop the engine immediately when the light comes on, (just as you would with a car) but perhaps you need to get somewhere to safety: so the engine will continue to run at low power to facilitate that -- at the risk of permanent engine damage, however.
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Old 01-04-2020, 16:10   #5
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Re: Tohatsu Outboard check oil light coming on

OP here: this is an old thread but since it got revived I figured I should update: I was eventually able to fix the problem by switching to 10-40 oil instead of 10-30. The Tohatsu manual seemed to recommend 10-30 for the temperatures we operate in, but also allows use of 10-40. That seems to have gotten rid of the oil pressure issue. Hurray!
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Old 01-04-2020, 17:24   #6
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Re: Tohatsu Outboard check oil light coming on

Err, no. Changing to slightly higher viscosity oil didn’t fix anything, it may have slightly bumped the oil PSI a little, but if you really do have low oil PSI, you need to get that fixed, and soon while you still have a functioning motor.
I bet it’s a pressure transducer and not actually low pressure.
However in this case in my opinion you need to get a dealer to fix it, normally I’d say start with a direct oil pressure gauge yourself, and you still can, but I think it best to take it to or at least call a dealer, who knows maybe there is a recall or an ECU flash to fix exactly this?
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Old 02-04-2020, 03:34   #7
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Re: Tohatsu Outboard check oil light coming on

The difference between 10W-30 and a 10W-40, is the high temperature viscosity. Obviously, a 10W-40 (40 Deg C/104F) is thicker than a 10W-30 (35 Deg C/95F) at high temperature.
Using oil with a viscosity that is too high can result in excessive oil temperature and increased drag. Using an oil with a low viscosity can lead to excessive metal to metal contact between moving parts. Using the correct viscosity oil eases starting, reduces friction, and slows wear.
I can't imagine PNW (Seattle) temperatures often exceed 35C/95F, but if they do, 10W40 would be your choice (perhaps synthetic).
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Old 02-04-2020, 04:22   #8
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Re: Tohatsu Outboard check oil light coming on

This happened to me. I changed out the oil pressure sender and it fixed the problem.
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Old 02-04-2020, 05:03   #9
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Re: Tohatsu Outboard check oil light coming on

I'll throw my $0.02 in.....


Since we agree that the low oil pressure indicator light is coming on here are the possible issues, off the cuff, not necessarily in order of trouble shooting.


1) check for a minimum spec for oil pressure (usually 5 psi)
2) If possible, install a mechanical guage in the oil line, possibly in place of sensor?
3) If pressure is below spec. there are really only 2 possibilities a) crap oil that is more like water b) Oil pump wear making too large clearance between rotor and housing.


IF the pressure is above minimum spec. the pressure sensor is out of spec. warranting a change of the sensor.



Story:


I took my NEW Dodge Dakota in for it's first oil change to Mr. Lube and on the way from the lube shop the oil light started flickering at the first stoplight I came to. It was bulk oil pumped from a drum..... much akin to water, Me thinks)


I spun the truck around and took it back to them and demanded they change the oil out for stuff that comes from bottles and it was fine after that.



For those that don't know it, 10WXX oil is REALLY 10 weight base oil, that uses "Viscosity Improvers" to thicken it with temperature, but it is STILL 10 weight oil!.


Assuming the weather is warm enough, you might consider using straight 30 weight oil, then you actually get thicker oil!


Given that you added a couple or 3 PSI of oil pressure with thicker oil, I am assuming that you have oil pump wear issue.


How easy that is to address depends on where the oil pump is located on the engine. IF it is external, I would change the cover and gasket. It is likely aluminum and the most likely part to wear. The steel rotor would be the next part. (unlikely)


Good luck, hope this helps!


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Old 02-04-2020, 05:13   #10
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Re: Tohatsu Outboard check oil light coming on

Very unlikely its oil pump wear, much more likely a stuck open oil pressure relief valve.
Not that I have overhauled a huge number of motors, but I have never seen an oil pump worn to the point that it has low oil pressure, but have seen more engines than I can remember that were so worn that they were the cause of low oil pressure.

However this is a new motor, so we should be able to say that excess wear is very unlikely, unless it’s continued to be operated at a very low pressure, if in fact the pressure is actually low.
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Old 02-04-2020, 11:03   #11
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Re: Tohatsu Outboard check oil light coming on

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I Occasionally, about 1 in 20 runs, the engine starts losing power in brief spurts - like the rpm is dropping for a second or two or almost like it's going into neutral and back into forward. Other than this 5% occurrence, it runs well, sounds good, cooling water is always flowing, and it's not smoking or showing other red flags.
The warning light on my Tohatsu5.5 is busted, so I donít know anything about your flickering light. The occasional loss of power is probably your propeller torque hub (not sure of nomenclature) beginning to disintegrate. Basically, the propeller is connected to the drive shaft with a hard rubber hub. The rubber hub takes the place of the old shear pins in transmitting torque to the prop, while protecting the drivetrain should the prop hit something solid.

The hub is not replaceable by itself - you need to buy a new Tohatsu prop (shades of Apple!). I hacked another fix with an aftermarket prop that has a replaceable hub. I figure that overtime I will save money this way - and no one in La Paz had a Tohatsu prop for me to buy anyways.

One of these days I will get around to replacing that warning light.
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