Blowing Fuses

TimTJR

Seaman
Joined
May 17, 2018
Messages
69
Hi,
I have a Crownline with a 2007 4.3 Mercruiser TKS, Alpha 1 Gen 2. I blew two fuses 4 times last weekend. One was a 15 amp fuse and the other was a 20 amp fuse. One was in the wiring harness next to the carburetor and the other was hidden behind the distributor cap. (I can get the colors of the wires when I get home if needed). They seemed to blow when I was pulling a tube so the boat was under a load. It didn't blow while the boat was in motion. They blew when I restarted the engine after I turned the ignition off to let the tuber get back in the boat. When I replaced the fuses and immediately started the motor, it would run for 3 to 5 seconds then blow the same two fuses. When I replaced the fuses, and let the engine cool, the motor would start up and run fine as long as it was cooled down, and wasn't under a load or driving it hard. The last time it blew the fuses, I noticed my temperature gauge was a little over 180 degrees. So I replaced the fuses and let it cool down. When I turned the power switch for the battery back on, I noticed the fuel pump stayed running. Once it went down to 160, I started it back up and drove it to the boat ramp. Got it loaded on the trailer and the engine would not shut off even after turning the key off and pulling it out. I had to trip the 50A breaker to turn it off. So, I got on some forums and learned that the TKS diode is probably shorted out so I did the tests and confirmed it is bad. So I ordered a new one and it has arrived. I read one persons post that he replaced his TKS diode and blew it again immediately and he later found his thermal switch (PN 866089) was bad. Does anyone have any instructions on how to test the thermal switch? I am trying to make sure I check everything before putting the new diode back in to prevent shorting out a brand new one.

My engine has 192 hours on it. I heard the impeller needs replaced every 100 hours. Should I go ahead and replace it? I am trying to figure out why it is getting so hot. The audible alarm never sounded so I am not sure what temp it needs to get to in order to trigger the alarm.

Is there a safety feature that blows fuses if the temp goes over 180?

I appreciate any help I can get. Thanks
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Is there a safety feature that blows fuses if the temp goes over 180?

No.

Sounds like the diode or the temperature switch may be shorted. You'll need to get in with a multimeter and do some trouble shooting.

Chris.....
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
It is true if the diode shorts the motor will continue to run. In the drawing below, power comes from the 20 amp fuse to the Thermal switch, then TKS module. When the diode shorts power will also go to the fuel pump.

The thermal switch will not cause the diode to short out, it is just a switch. If the switch did short then the 20 amp fuse would blow. The fuel pump has its own fuse (not shown).

If the TKS module is drawing to much current it also can blow the 20 amp fuse

What was the wire color for the 15amp fuse?



TKS V6 and V8 wiring.jpg
 

TimTJR

Seaman
Joined
May 17, 2018
Messages
69
The 15 amp fuse has one wire pink with purple stripe, and one wire red with black stripe .
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
The Red/Black should be Red/Purple (20 amp)
The Pink/Purple has me stumped, and it may be something that was added by a Prior Owner (PO)

Can you post a pic?
 

TimTJR

Seaman
Joined
May 17, 2018
Messages
69
It says file too large. Let me see if I can figure out a way to reduce the size by phone
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
If you can also post a pic of the whole motor also
 

TimTJR

Seaman
Joined
May 17, 2018
Messages
69
So sorry .The 20 amp has red/ purple wire ., and a pink wire .

The 15 amp has red/black (maybe it red and purple, hard to tell because it's way back in there) and pink/ purple .
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
I'm not finding the Pink/(other color) in my TKS manual. It is most likely that Merc changed some wiring and is a newer manual then the one I have. If I use the MPI and TKS, there is a possibility that the 15 amp fuse was for the fuel pump. If so there would also may be a relayon the motor for it

What is your motor serial number?
 

TimTJR

Seaman
Joined
May 17, 2018
Messages
69
I am heading out of town right now. When I get back Sunday I will try to trace the wires to see where they go. I will also check for any bare or damaged wires while im at it to rule that out.

Do you know if these diodes just go bad or does something usually cause them to go bad?

Also I don't know why my motor is getting so hot .
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
Do you know if these diodes just go bad or does something usually cause them to go bad?

The diodes are barely able to handle the current passing thru them. So if something starts drawing more then normal, after a period of time they overheat and short out. You can buy a heavier diode and it will work the same without issue, just need to adapt to wire it in

Also I don't know why my motor is getting so hot .

The impeller should be replaced by time or hours, but time has more importance then hours. If the boat is used year round it will last a long time, but having it sit thru the winter is hard on them. The Gen 2 drive impeller last longer then the Gen 1, but when you first start seeing a overheat issue, its always best to start by replacing the impeller.
 

TimTJR

Seaman
Joined
May 17, 2018
Messages
69
Yeah I use it a lot during the summer but not at all during the winter. I bought it last fall so I don't know when the impeller was last changed. I will go ahead and change it.

Does driving it hard cause more current to go through the diodes? Or do you think I might have something else wrong that I need to diagnose?
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
...Does driving it hard cause more current to go through the diodes? ...

No. Current is a function of voltage and resistance. Worth checking the alternator output voltage though. Should be 13.8 to14.4 volts.

Chris...
 

TimTJR

Seaman
Joined
May 17, 2018
Messages
69
The thermal switch will not cause the diode to short out, it is just a switch. If the switch did short then the 20 amp fuse would blow. The fuel pump has its own fuse (not shown).





The 20 amp fuse does blow. I bought a new diode but have not replaced it yet. Is there a way to test the thermal switch? The temp gauge seems to work correctly on the dash. The needle doesn't bounce around or do anything crazy. I was not able to find any bare wire or any damaged wires.

I purchased an impeller kit for my "running hot" issue and will be replacing that here within the next couple days when I get a chance. I have already taken the bottom off and looked at the impeller and it really doesn't look bad but I will replace it anyway since I got it apart.
 
Top