mercury blackmax 150 overheating?

mjchoochoo · Mar 26, 2004

after starting the motor, the temp guage steadily rises and doesn't stop. within about a minute, the needle is pegged. at the same time, the engine does not feel hot to touch and the water out the pee hole isn't hot, only warm. any help?

Virago85 · Mar 28, 2004

Re: mercury blackmax 150 overheating?

sounds like the sencer is bad

dogsdad · Mar 28, 2004

Re: mercury blackmax 150 overheating?

Liljim, are any of your other instruments acting up at all? I have been having a similar problem with my 135. It looks as though my stator has a shorted coil and I am 99.44% positive that it is causing my temp gauge to read high. I have measured the temp of the telltale water with a cooking thermometer, and I have measured the cylinder head temps with a laser/IR thermometer, and there is no real temperature problem. The other clue that the temp reading is false is that the overtemp horn does not activate, and I know that it works. I would suggest looking closely at the stator windings that feed the rectifier. I am positive that when I get around to replacing the stator, my bad readings will go away. Hope this helps! -dd-

KCLOST · Mar 29, 2004

Re: mercury blackmax 150 overheating?

dogsdad, I'm not really following your conclusion... Most temp guages that I'm aware of are not connected in any way with the stator. You have a live wire from the console to power the guage. The sending wire runs from the sensor to the guage directly. And a ground wire from the guage to ground at the console... If the sending wire is grounding out to the block somewhere that will cause the guage to max out... But a gradual increase doesn't support that possibility... I just don't see how a stator problem could possibly affect the guage... It should run of off 12v DC from the battery through the KEY switch. To check the guage, I would ground out the sendor wire "s" and see if the guage goes to max, if it does it should be ok. Also, if it's a teleflex guage/sensor you can remove the sensor from the block. Remove the wire from the sensor and ohm it out. It should measure 600-1000 ohms at room temperature.

dogsdad · Mar 29, 2004

Re: mercury blackmax 150 overheating?

KCLOST, my temp gauge has been giving a false reading ever since I had an overheat incident last summer, due to a destroyed impeller. The heat took out one of my switchboxes too, and once that was replaced the boat ran just fine, but the temps read high. I got to looking at the electrical system a few weeks back and discovered that the charging coil in my stator has a short---as if the coil was tapped to ground. The two wires from that particular coil, as you know, go to the rectifier. There is an output from the rectifier which charges the battery, but there are other wires connecting the instuments, I believe, to one side of the charging coil of the stator. I think it's a gray wire that goes to the control box instrument connector, it's been a few weeks since I looked at it. As I look at my wiring diagram at this moment, it occurs to me that the gray wire may be what drives the tachometer...hmmmmm. Is that correct? Anyway, I digress. I think that I had a damaged rectifier from way back, but I smoked it entirely last month when I was hooking up the battery (I cannot carry on a conversation with my wife and do these things safely, it seems) and reversed polarity. Until I put the new rectifier on, my tachometer was inaccurate and gave high readings since the overheat incident. Now it is accurate. I am finding this electrical system to be somewhat mysterious, at least as far as relying on the manual goes...but, because of how I saw the tach behave with a damaged rectifier, and how it straightened out with a new one, I am pretty darned positive that the temp gauge will be accurate again once the electrical system is restored. -dd- PS: I will folow up on your suggestion on ohming out the sensor. I think my instruments are indeed Teleflex...my friendly local boat dealer doesn't seem to know a thing about getting a new sensor---I asked about that long ago and all I got in response was a look from him like I had instantly grown a second head. I called it a sending unit---maybe I confused him. But it shouldn't have!

Mettaree · Mar 30, 2004

Re: mercury blackmax 150 overheating?

Run the motor until you get a high reading on the gauge - shut down the motor(turn off ignition) - turn on ignition - gauge running on straight battery - no charging happening. See where gauge is now. Check switched 12V at gauge. Is the gauge the right one for the resistance range of the temp sender?

KCLOST · Mar 30, 2004

Re: mercury blackmax 150 overheating?

You should have a fuse(s) that will control the voltage going to the console and guages.... Rectifier only charges the battery, it shouldn't affect guages if fuses protect the circuts... Rectifier will affect Tach however... That grey wire goes to the sender connection on the Tach Guage. My point is, if you have 12+Volts DC powering the guage, the only thing affecting it's reading is the sensor and it's resistance relative to temp. If its faulty you're readings will be off obviously.... Try what JKW suggests, that will prove it's not an electrical/charging problem...

dogsdad · Mar 30, 2004

Re: mercury blackmax 150 overheating?

Liljim, I didn't mean to hijack your thread. Hopefully all this info will benefit you as much as it does me. Another question, though: Why is one side of the charge winding of the stator tied to the regulator? JKW's suggestion is a good one. Why didn't that occur to me? I guess that's why they say two heads are better than one! -dd-

KCLOST · Mar 30, 2004

Re: mercury blackmax 150 overheating?

The regulator leads come from the rectifier, not directly from the stator... Stator wires go to rectifier, then one red from rectifier to regulator and one yellow from regulator back to rectifier....

dogsdad · Mar 30, 2004

Re: mercury blackmax 150 overheating?

Those points are electrically the same. The thing could be connected stator-regulator-rectifier and it would make no difference. The physical layout is of no consequence to electron flow. It is zero ohms from the coil in the stator to the regulator.

KCLOST · Mar 31, 2004

Re: mercury blackmax 150 overheating?

Yes! With a faulty regualtor you could fry your battery, if I understand it's function correctly.....

dogsdad · Mar 31, 2004

Re: mercury blackmax 150 overheating?

Agreed. The purpose of the rectifier's output being tied to the regulator is pretty self-explanatory...but I would like to know why the yellow wire from the rectifier---which is electrically also the output of the stator---is also connected to the regulator... So many questions, so little time!

-dd-

KCLOST · Mar 31, 2004

Re: mercury blackmax 150 overheating?

The regulator, regulates the electrical current (IF Necessary) that comes from the stator. That's all the stator does, is generate electricity to power the switchboxes and recharge the battery through the rectifier/regulator system where the rectifier coverts AC to DC.

BF · Mar 31, 2004

Re: mercury blackmax 150 overheating?

Hiya, the advice is all good I think, I just wanted to comment on fuses... KClOST wrote:

You should have a fuse(s) that will control the voltage going to the console and guages.... Rectifier only charges the battery, it shouldn't affect guages if fuses protect the circuts...

maybe I'm reading more into that than you intended, but fuses don't "control" voltage... all they do is burn up if there is too much current drawn through them (that's why they're rated in amps) if there is a cruddy/spikey/low/high voltage on one side of a good fuse, it'll look the same on the other. I agree with you that if the gauge has a good 12V, then it'd be the sensor or sensor wire, but I'm not sure whether a charging system putting out weird/spikey voltage might not also corrupt the 12V on the power supply lines to the gauge, and possibly make it do funny things (?). Having said that, my bet would be on a bad sender. You could disconnect the power lines for the gauges from the main battery, and attach them to separate battery (without the charging system attached). If temp then reads properly, then I'd believe in the charging system idea. hope this helps.. Brent

KCLOST · Mar 31, 2004

Re: mercury blackmax 150 overheating?

Good point, but the fuses are there to protect what is connected through them... Excessive current/shorts through the fuse will cause it to trip/fail therefore preventing further damage to the wire/guages.... My description of voltage was not proper

That's the regualators job, so to speek..

dogsdad · Mar 31, 2004

Re: mercury blackmax 150 overheating?

I think I should clarify a point also, which is one of my questions...we all agree that the rectifier's output is regulated for charging the battery..simple. What I want to know is: why is one of the INPUTS to the rectifier (which is electrically the same point as one side of the charging coil in the stator) tied to the regulator? I find that somewhat odd.

KCLOST · Apr 1, 2004

Re: mercury blackmax 150 overheating?

Because the voltage that charges the battery through the rectifier, comes from the stator! Thus it must be tied to the regulator in some way...

dogsdad · Apr 1, 2004

Re: mercury blackmax 150 overheating?

Yes. That is why the OUTPUT OF THE RECTIFIER is connected to the regulator. That does not explain the INPUT to the rectifier being connected to the regulator. The output of the stator is alternating current. The rectifier converts it to direct current. The regulator then limits the voltage value of the direct current for keeping the battery charged. End of story.

My question is: why is one side of the stator's charging coil tied to the regulator? -dd-

mercury blackmax 150 overheating?

Recruit

Petty Officer 2nd Class

Lieutenant

Commander

Lieutenant

Petty Officer 1st Class

Commander

Lieutenant

Commander

Lieutenant

Commander

Lieutenant

Commander

Lieutenant

Commander

Lieutenant

Commander

Lieutenant