Yamaha 115HP V4 Voltage / Temperature questions

[AK115V4-93]

Hi all,

I’m looking for some advice regarding voltage and engine temperature on a two stroke 1993 115HP V4 Yamaha outboard (model 6E5 - long leg - 115BET).

I recently purchased this outboard and have performed a complete service on it. Cosmetically it is in virtually perfect condition and looks new for its age. Upon starting it for the first time I noticed my volt gauge was reading rather high on the dash of the boat. What I would like to know is the following voltage and temperature readings normal?

I performed some testing to gather as much information as possible. As a result this will be a lengthy post!

All tests performed with boat on the trailer and flushing muffs providing cooling water.
Outboard idle speed (from connected tacho): 900 RPM

Compression Test
• Tested with motor warmed up – run for 15 minutes
• All sparkplugs removed
• Ignition disabled via safety lanyard removed
• Throttle WOT, lower unit in neutral
• Each cylinder cranked 2 times for same duration
• Outboard starts and idles perfectly (on muffs at least, haven’t water tested yet)
• Cyl 1: 125PSI, Cyl 2: 127PSI, Cyl 3: 130PSI, Cyl 4: 127PSI

So in terms of voltage readings I used a good quality multimeter at the battery terminals.
Battery has been fully charged via a smart battery charger several days before this test.

Battery at rest (sitting for a few days): 12.7 Volts
Battery cranking: 10.4 Volts
Battery voltage when outboard running (just after cranking at idle speed 900 RPM): 12.9 Volts
At 1500RPM: 14.6 Volts
at 2000RPM: 15 Volts
After 8 minutes at idle (900rpm): 14.4 Volts
After 15 minutes of running (taking reading at 900rpm idle): 14.5 Volts (dash volt gauge shows 15v)

How do these voltage readings look? I don’t want to boil my battery or damage any on-board electrical gear. I assume the outboard has a regulated rectifier? Is anything amiss? I was concerned with the 15 volts at 2000RPM.

In terms of engine temperature, I have two aftermarket temperature gauge senders installed into the Yamaha factory purpose made ports on top of the cylinder banks where they show to install pressure and temperature senders. Motor tell tale is very strong at idle.

Readings are as follows (on muffs):
After 8 minutes of running:
• Port bank: 58 Celsius (136.4 Fahrenheit)
• Starboard bank: 41 Celsius (105.8 Fahrenheit)

After 15 minutes of various engine speeds, but reading at idle after waiting a few minutes:

• Port bank: 59 Celsius (138.2 Fahrenheit)
• Starboard bank: 50 Celsius (122 Fahrenheit)

The port bank is noticeably warmer to the touch than starboard as per the gauge readings. I can hold my hand on the port side without discomfort. So far temps don’t rise any higher but the test only went for 15 minutes on the muffs with a garden hose.

I expected both sides to be more or less similar. No overheat alarms or anything. Again motor has not been run on the water yet.

So:
1. Anything out of spec here?
2. Should I be concerned with battery voltage or engine temperature at this point?

Edit: Forgot to mention I did a continuity test on the rectifier terminals with the engine off as per the OEM engine service manual. It fails most of the tests – i.e. I don’t get any continuity when the manual says I should. Only a few combinations pass the test. Multimeter set to continuity mode.

[AK115V4-93]

Is anyone able to provide some advice?

[boscoe99]

I don't see any cause for concern.

[zenoahphobic]

Is anyone able to provide some advice?

Nothing wrong there, the readings are the same downunder as they would be for a good engine upover.

[AK115V4-93]

I don't see any cause for concern.

Nothing wrong there, the readings are the same downunder as they would be for a good engine upover.

Thanks for the replies

So I shouldn’t be concerned with 15 volts at 2000RPM then? I was under the assumption this is bad for your battery. I was actually going to replace the rectifier as I thought it was overcharging. If this is normal then I guess I have nothing to worry about and have saved a fair bit of $ in terms of not replacing the rectifier!

I’ll see what the temperature reaches on the water. What should I look for in terms of a safe operating temperature per head?

[zenoahphobic]

Thanks for the replies

So I shouldn’t be concerned with 15 volts at 2000RPM then? I was under the assumption this is bad for your battery. I was actually going to replace the rectifier as I thought it was overcharging. If this is normal then I guess I have nothing to worry about and have saved a fair bit of $ in terms of not replacing the rectifier!

I’ll see what the temperature reaches on the water. What should I look for in terms of a safe operating temperature per head?

For a normal 12v lead acid battery ideally charging should be set between 13.8v and 14.5v.

Your 15v at 2000rpm indicates that your battery is good and charged. A failing battery would probably read another volt higher on this engine. This might appear a bit high to you, but the charging is not so precise on this engine. Provided that your battery is of correct Amp/hour and CCA this doesn't seem to destroy the battery.
For many years I have used N70z 650-700 CCA batteries on this engine without obvious detriment. But I tended to do short runs with waterskiing and fishing. Cruises would be nolonger than much more than one hour; this type of stop and start (using the battery every start) would be typical use envisaged in applications with this engine.

Also how accurate is your multimeter? The continuity setting may not be the correct setting to use testing diode rectifiers. Ohm setting of atleast 2000ohm measuring forward and then reverse should show different readings if OK.

[AK115V4-93]

For a normal 12v lead acid battery ideally charging should be set between 13.8v and 14.5v.

Your 15v at 2000rpm indicates that your battery is good and charged. A failing battery would probably read another volt higher on this engine. This might appear a bit high to you, but the charging is not so precise on this engine. Provided that your battery is of correct Amp/hour and CCA this doesn't seem to destroy the battery.
For many years I have used N70z 650-700 CCA batteries on this engine without obvious detriment. But I tended to do short runs with waterskiing and fishing. Cruises would be nolonger than much more than one hour; this type of stop and start (using the battery every start) would be typical use envisaged in applications with this engine.

Also how accurate is your multimeter? The continuity setting may not be the correct setting to use testing diode rectifiers. Ohm setting of atleast 2000ohm measuring forward and then reverse should show different readings if OK.

I see right. The 13.8v and 14.5v agrees with what the so called "battery experts” told me when I visited the store. (I tend to not trust salesmen in stores)

The battery I have is a Century Marine Pro 580 (580 CCA, 695 MCA, model D23RM) that is from 2010 but appears to still be going strong. Link: Marine Pro 580
I plan to upgrade to the 730 (N70ZM model) when this dies.

The boat is also a ski boat and I do a lot of stop and starting. I wouldn’t cruse more than 20 – 30 minutes at a time. I always keep the battery fully charged via a smart charger to ensure all is healthy.

Regarding the multimeter, I used a Fluke branded unit that my electrician mate uses for his work in the electrical trade. I used the continuity setting that displays the Ohm value on the display and sounds the buzzer when a closed circuit is detected. Furthermore I had the engine turned off, battery disconnected.

Perhaps I should retest according to the manual and the multimeter setting you suggest and see if I get results as per the OEM service manual.

So essentially I am getting the idea that my rectifier and charging system is all ok and there is no need for concern (or part replacement) and in fact 15 volts is acceptable.

[AK115V4-93]

Update

Update:

Regarding voltage:
I did discover this engine has a regulator rectifier, not just a rectifier. I also discovered that my regulator rectifier (R/R) was faulty.

How did I find this out?

• I had issues with my tachometer – One would bounce, another would show no reading.
• My voltage was high. Before I was getting 14 volts at idle, and 15 volts at 2000RPM.

After I replaced the R/R:

• Tachometer works correctly
• Voltage sits at 13.8 volts, maxing out at about 14 volts after many hours on the water with a fully charged battery.

Regarding engine temperature:

In the water

• Port and starboard banks sit at about 50 degrees Celsius (122 Fahrenheit) all day.
• Only warming up to 60 degrees Celsius (140 Fahrenheit) when the engine is shut down. Soon as it is restarted back down to 50C.
• No alarms or anything of the sort

I had uneven temperatures before, but after changing the thermostats both banks have mostly evened out. Engine runs hotter on muffs than in the river.

Also:
Testing the old R/R failed as per the instructions in the Yamaha Service Manual but testing the new one also failed. Either I am testing it wrong or the manual is incorrect.