Gauges, etc

[CharlieZulu]

Just picked up a 1987 vintage Merc 90, and ordered a manual for it. It is connected to this boat:

My boat has a speedo and tach only (and the tach doesn't actually work, although when I turn the ignition on, the needle does jump a bit, so I guess there is power there)

Anyway, I'd like to add some gauges so I know what's going on in there. Voltmeter is pretty straightforward (will wire it directly across the battery, after my switch) but here's my question:

Does this vintage Merc have the necessary sensors built in to measure water pressure, flow etc?

Also, I do not hear an alarm when I turn the ignition to ON -- same question, does this motor (90 hp 1987, serial number starts with a B) have this stuff built in, somewhere? Where is the little speaker usually located?

I did notice a couple if wires had been snipped off back there. I want to take care of this motor and I hate not knowing what's actually going on back there.

Thanks in advance.

 

[Chris1956]

Re: Gauges, etc

Charlie, Those old inlines may have a warning horn for the autoblend system. If your autoblend system has been removed to run premix, it may have been taken off. The horn looks to be mounted on the remote oil tank in the boat.

For the gauges, a voltmeter is good, but you can wire it anywhere on the dash, to any +12VDC source that runs the other gauges. A tachometer is good. See if the signal wire is connected to one side of the stator. Stator has 2 yellow wires, and the tash signal wire connects to one of them at the rectifier. Tach signal wire is likely grey. Power for the instruments is likely purple.

I recommend a water pressure gauge and a fuel gauge to round out the instruments. As long as you have consistant water pressure, the motor should not overheat. Put in a new impeller and note the water pressure.

 

[CharlieZulu]

Re: Gauges, etc

Hi Chris1956:

I'm not familiar with your terminology, but if by 'autoblend' you are referring to 'oil injection', then I do have that, yes. i.e. there is a oil tank right there on the side of the motor, with a visual level indicator tube.

I think I need to understand what this audible warning alarm thing is supposed to do -- and how exactly it works and what exactly it's connected to.

On the gauges, I agree, more is better but again, I haven't a clue how these gauges interface with the motor. (I don't even know how my speedo works!) To some extent, I hope to learn a lot more when my manual arrives.

Specific question on the voltmeter: what I'd really like is an LCD digital readout style (like I have on the face of my handheld multimeter), rather than a needle gauge where I can't really resolve the difference between 13V and 14V, say. Are these available?

Can you tell this is my 1st boat, or what?

 

[Chris1956]

Re: Gauges, etc

Autoblend is Mercury's term for oil injection. I had thought a lot of those old systems had been disconnected. You might make a new post asking if you should remove yours. Laddies and some other experts have good insight into those systems. I think the only alarm is low oil, connected to a float in the oil tank.

I do not know if you can find a digital voltmeter, but since you have an unregulated system, do you really care what it says? As long as it is >12VDC, the motor is charging.

The speedo works on water pressure. While the boat moves, it forces water up the tube to the gauge.

The tachometer works off the stator. it counts ac voltage spikes and converts to RPM.

The water pressure gauge is mechanical. A pipe nipple is inserted into one side of a brass tee, which replaces the plastic elbow that feeds the telltale water indicator. The telltale elbow fits the other side of the tee.

 

[corm]

Re: Gauges, etc

Hi,
The 3 cyl 90 HP does not have the vacuum auto-blend system it has a gear driven system. They work just fine.

 

[CharlieZulu]

Re: Gauges, etc

Autoblend is Mercury's term for oil injection. I had thought a lot of those old systems had been disconnected. You might make a new post asking if you should remove yours. Laddies and some other experts have good insight into those systems. I think the only alarm is low oil, connected to a float in the oil tank.

Sorry -- I don't get it...... why would I want to remove my oil injection system?

I do not know if you can find a digital voltmeter, but since you have an unregulated system, do you really care what it says? As long as it is >12VDC, the motor is charging.

I managed to find one on ebay, we'll see what happens! (Also, can you provide more detail.... my system is 'unregulated'? What does this mean?



Thanks again for the great advice and comments, folks.

 

[stackz]

Re: Gauges, etc

I've got that exact motor on my 1990 thundercraft which I'm restoring.

I'm using http://www.sscompetition.com/ gauges. they were the cheapest ones I could find in the set size I wanted and had good reviews.

I just got the tach/water temp/volt/tilt-trim gauges hooked up last night. the speedo will have to wait until I get back in the water before I can properly test them. I'm going to test the water pressure gauge by this weekend as I'm tapped for $$ until midnight and the T-fitting for splicing it in is in my g/f's car sigh.

overall they look great and the ones I've got hooked up work just fine off the control output harness from the engine. the water temp gauge even works off the mercury sending unit.

the water pressure gauge, I'm splicing into the water pump pee hole inside the cowling. the tube for the pee hole runs along the bottom left of the engine to the bottom left side of it where the exit from the block is.

just cut the line where you're comfy and then run a tube from the "T" portion of the T-connector you put inline to the back of the gauge and you're done.

hope this helps.

 

[Chris1956]

Re: Gauges, etc

Charlie, the early Autoblend systems were considered by some to be unreliable. I never had one, so I have no educated opinion.

The charging system consists of a stator and a rectifier. As the motor spins faster, the stator produces higher voltage. The battery is used as a load, helping to regulate the charging. There is no voltage regulator and no thermostat. A water temp gauge will read dead cold at idle and warmer at cruise, if it even works that good. As far as I know Merc never made a trim gauge or an overheat alarm for those motors.

 

[corm]

Re: Gauges, etc

Hi,

Here is a picture of you overheat alarm sensor no 22
http://www.crowleymarine.com/mercury_parts/298/10.cfm
and the thermostat No 31.
Your gear driven oil pump pumps the oil into the fuel pump where it is mixed with the gas before it goes into the carbs. It is a nice system.
http://www.crowleymarine.com/mercury_parts/298/22.cfm
Pump is No 24, Gear is no 27 which is inside the engine block.
Easy to read gauges.
http://www.2kracing.com/Universal_Subcategory/Gauges/Volt_Gauges.html

 

[stackz]

Re: Gauges, etc

Charlie, the early Autoblend systems were considered by some to be unreliable. I never had one, so I have no educated opinion.

The charging system consists of a stator and a rectifier. As the motor spins faster, the stator produces higher voltage. The battery is used as a load, helping to regulate the charging. There is no voltage regulator and no thermostat. A water temp gauge will read dead cold at idle and warmer at cruise, if it even works that good. As far as I know Merc never made a trim gauge or an overheat alarm for those motors.

there is most certainly a thermostat on these engines. I know that for a fact as I just had to change mine out.

mine also has a trim sensor on it down on the power trim unit and it uses a brown/white wire to the gauge.

 

[Chris1956]

Re: Gauges, etc

Sorry, Crowley lists a 1987 6 cylinder inline 90HP motor. That is the one I was referring to.

 

[CharlieZulu]

Re: Gauges, etc

Geeeeez, this is an awesome forum! Thanks guys for all this info!!

I just bought this boat 10 days ago, and there is so much to learn, and... the season up here is ending so quickly. I won't be back to my weekend place for another coupla weeks -- can't wait to start messing around and doing these mods but the weather is gonna slow me down.

Thanks again for the help.

Chris
(CZ)

 

[stackz]

Re: Gauges, etc

Sorry, Crowley lists a 1987 6 cylinder inline 90HP motor. That is the one I was referring to.

ah ok. these are inline 3's. thermostat is a little egg looking thing. weirdest t-stat I've ever seen...