I can't get my mercruiser over-temp alarm to shut off

[rodgeml1]

Re: I can't get my mercruiser over-temp alarm to shut off

Are you serious?!?!?!??? A leaking 'O' ring is enough to totally destroy a drive, and you're going out KNOWING you have a broken one.... My god man!!!

Now, the alarm circuit is incredibly simple. 12V goes from the ignition switch (in the ON position) to the alarm module (the siren under the dash), and has 1 Normally Open and 2 Normally Closed switches on the engine, one switch for water temperature (NO), one switch for oil pressure (NC, but open when oil pressure present) (these are NOT the sensors for the gauges), and one switch in the bottom of the leg oil monitor bottle (NC, but open with oil in the bottle). From these switches the current path is to ground.. If any one of these switches closes during normal operations, the alarm sounds. FYI, no relays or even fuses in this circuit...

If the alarm is sounding quietly after you had copious quantities of seawater hose down your engine, then I would suspect one (or more) of these switches has got wet (surprise, surprise!) and is now providing a resistive path to ground.... Wet electrics will also explain all your other symptoms.... Dry out the electrical system, clean all the switches and sensors....

You have a Thunderbolt IV system, but what I didn't see there is the ground wire from the distributor to the engine block... you should find a spare ground wire in the harness next to the distributor. Remove one of the module mounting screws and put the ground wire under that....

Chris......

Great information here....thanks! I'll jump on running the electrical issues to ground and see what I can find.

Do you think an electrical issue can be causing the reduced RPMs?

 

[rodgeml1]

Re: I can't get my mercruiser over-temp alarm to shut off

Update:

I have pulled the tape off of the wire bundles in order to trace where everything is going. The last person to work on the electrical system either had no clue what he was doing or was making a concerted effort to bypass certain features of the system as I found A LOT of disconnected wires. I found two ground wires disconnected and dangling, both wires under the gear lube oil reserviour were disconnected, and the purple lead (see diagram below) from the oil pressure sender was disconnected (I can't seem to find from where it came loose). I'm in the process of getting all of that hooked back up like it's supposed to be and I still have to pull the coolant temperature switch to make sure it's good.

With all of this having been disconnected, I'm surprised the auditory alarm system worked at all. But the fact that it went off after the water pump tube came loose leads me to believe it was, at least before the incident, working properly.

According to Don (and other research), there is no rev limiter/slow mode for this boat. Does anyone have other suggestions as to what might be causing the governed RPM (no greater than 2800)?

 

[rodgeml1]

Re: I can't get my mercruiser over-temp alarm to shut off

I think you got water in your oil from the oil cap. Bad design caps. Should flush the oil and change filter. You got a blowby. How old is the motor (rebuilt?)

The outdrive has been rebuilt and I believe it's a 1995 model.

 

[riptorn]

Re: I can't get my mercruiser over-temp alarm to shut off

I do have some water intrusion into my lube oil. I had just serviced the lube oil and the level in the reservior was right at the line. When I got back home, I noticed the oil was milky. When I opened the lid to the reservior, oil started oozing out, and there were air bubbles that gurgled up. I've taken a sample from the lower drain plug and have it set aside to see if it separates.

My 78 in line 6 was rebuilt also and still had a blow by through the oil cap which makes me believe water can get inside also. It takes a few oil changes to get the milky out..
Hopefully you don't have the serious problem which unfortunate members here been through.
wish the best.
P.S.
You are talking about the engine and not the o/b lower unit. Original post states you blew a water hose?

 

[04fxdwgi]

Re: I can't get my mercruiser over-temp alarm to shut off

Update:

I have pulled the tape off of the wire bundles in order to trace where everything is going. The last person to work on the electrical system either had no clue what he was doing or was making a concerted effort to bypass certain features of the system as I found A LOT of disconnected wires. I found two ground wires disconnected and dangling, both wires under the gear lube oil reserviour were disconnected, and the purple lead (see diagram below) from the oil pressure sender was disconnected (I can't seem to find from where it came loose). I'm in the process of getting all of that hooked back up like it's supposed to be and I still have to pull the coolant temperature switch to make sure it's good.

With all of this having been disconnected, I'm surprised the auditory alarm system worked at all. But the fact that it went off after the water pump tube came loose leads me to believe it was, at least before the incident, working properly.

According to Don (and other research), there is no rev limiter/slow mode for this boat. Does anyone have other suggestions as to what might be causing the governed RPM (no greater than 2800)?

View attachment 141978

With all these wiring issues, I would not be surprised to see bad grounds everywhere, causing resistance paths which can produce reduced voltages everywhere. This could cause a weak spark, severely hampering your performance of the engine, too.

Since there are so many wiring problems, if it were my boat, I would start from square one, at the batteries, and check every wire, especially the grounds, to ensure everything is connected correctly. One bad ground can have you chasing problems for hours, that really don't exist.

 

[dubs283]

Re: I can't get my mercruiser over-temp alarm to shut off

Does anyone have other suggestions as to what might be causing the governed RPM (no greater than 2800)?

well, you overheated your engine - compression test

when was the last FULL tune-up??

perhaps your drive is failing, you KNOW it leaks gear lube - thats pretty important, might want to get that one taken care of asap

other than that, get an OEM manual for your engine, figure out what you have for ignition and other electrical components and wire the harness and boat/guages, etc properly

once thats all done and you still can't get WOT, check the fuel system

 

[rodgeml1]

Re: I can't get my mercruiser over-temp alarm to shut off

My 78 in line 6 was rebuilt also and still had a blow by through the oil cap which makes me believe water can get inside also. It takes a few oil changes to get the milky out..
Hopefully you don't have the serious problem which unfortunate members here been through.
wish the best.
P.S.
You are talking about the engine and not the o/b lower unit. Original post states you blew a water hose?

I've flushed the outdrive oil once and will do so again to try and get it cleaned out.

Yes I am talking about the engine and not any part of the outdrive. The water coolant hose blowout was forward of the transom inside the engine well.

 

[rodgeml1]

Re: I can't get my mercruiser over-temp alarm to shut off

when was the last FULL tune-up??

I'm not sure when the last full tune-up was. I just bought the boat so I'm troubleshooting all of this with a lack of history.

perhaps your drive is failing, you KNOW it leaks gear lube - thats pretty important, might want to get that one taken care of asap

I had the drive checked out by a marine tech. He was convinced it was sound but your point is well taken. I've got a backup lower unit....if all of the other efforts doing relieve the issue, I'll change it out and see if that helps.

other than that, get an OEM manual for your engine, figure out what you have for ignition and other electrical components and wire the harness and boat/guages, etc properly

That effort is ongoign now. There is a lot within the boat that indicates electrical components aren't operating properly. I'm really hoping my problem lies there.

once thats all done and you still can't get WOT, check the fuel system

The fuel system has also proven to be finicky....I'm going to change out the fuel/water seperator to start and see hwo things go from there.

I have another question regarding the electrical system....does anyone know what the purple lead coming off of the alternator is for? It's the only loose and for which I can't find a home. The electrical schematic shows it sharing a note with the purple wire coming off of the coil. If I can't locate another termination point, I'm considering splicing it in with the purple coil wire and giving her a go.

 

[achris]

Re: I can't get my mercruiser over-temp alarm to shut off

I have another question regarding the electrical system....does anyone know what the purple lead coming off of the alternator is for? It's the only loose and for which I can't find a home. The electrical schematic shows it sharing a note with the purple wire coming off of the coil. If I can't locate another termination point, I'm considering splicing it in with the purple coil wire and giving her a go.

It's the 'Excitation' wire. As long as you solder it and properly insulate that would be just fine.

 

[Pete104]

Re: I can't get my mercruiser over-temp alarm to shut off

It's the 'Excitation' wire. As long as you solder it and properly insulate that would be just fine.

That won't find your missing revs, but if it makes you feel better.

When was the last time this unit ran right?

 

[achris]

Re: I can't get my mercruiser over-temp alarm to shut off

That won't find your missing revs, but if it makes you feel better.

When was the last time this unit ran right?

It might if the battery was low and not being charged.... Less power the ignition system could cause loss of revs....

 

[rodgeml1]

Re: I can't get my mercruiser over-temp alarm to shut off

That won't find your missing revs, but if it makes you feel better.

When was the last time this unit ran right?

The unit ran well leading up to the over-temp when the water pump line came loose, so if the low revs isn't related to that incident it's a REALLY unfortunate set of circumstances.

 

[rodgeml1]

Re: I can't get my mercruiser over-temp alarm to shut off

It might if the battery was low and not being charged.... Less power the ignition system could cause loss of revs....

The battery showed full charge before and after the precipitating event but I'll give it a fresh boost to rule it out.

 

[rodgeml1]

Re: I can't get my mercruiser over-temp alarm to shut off

Update:

I pulled the outdrive, completely serviced it, pressure checked it (and replaced most of the seals as a result), greased her up, replaced the lower shift cable, rewired it to be correct per the factory specs, put her back together, then hit the water. The boat started like a dream, shifted better than I could hope, and the alarm was gone. Unfortunately when I went to WOT, I still couldn't get above 2600 rpms. We went through all the itterations of changing up the timing, making sure the carb jets were providing enough fuel.....no go.

What I hadn't done was check the gear ratio of the outdrive. I know that should've been one of the first steps but I was so caught up in fixing all of the known problems I stopped troubelshooting everything else. Now, my engine (1995 4.3LX, 0F586331) calls for a gear ratio of 1.81. The stamp on the side of the outdrive that is currently installed says "1.47R". DOH!

Question: Is that difference in drive ratio sufficient to cut my RPMs almost in half at WOT?

 

[achris]

Re: I can't get my mercruiser over-temp alarm to shut off

...Question: Is that difference in drive ratio sufficient to cut my RPMs almost in half at WOT?

If you're running the same prop as the 1.81 was.... Absolutely!

As the prop pitch becomes too big, not only do the revs drop, but the horsepower available also drops, making it harder to turn such a big prop.... Vicious circle.

Changing that much on the ratio will have added an effective 5" of pitch. My boat runs to 4600 rpm with a 19" prop. I tried a 21" and it wouldn't make 4000.I suspect at 24" I would be struggling to make 3000.

The only question I'd have is... Does it struggle up to 2600? If it does, there's your answer, however if it leaps up to 2600, that ain't the problem...

Chris....

 

[rodgeml1]

Re: I can't get my mercruiser over-temp alarm to shut off

The engine doesn't struggle to get to 2600 RPMs but the boat doesn't come up out of the water at all.....very sluggish.

So I guess the next question is do I try to match the prop to the outdrive I have, or is it more advantagious to try and find an appropriately ratioed outdrive?