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Mercruiser 4.3L Battery Cable Lengths & AWG Sizes?

J

_jp

Contributing Member
Hi all,

My Maxum 1800 SR3 has a Mercruiser 4.3L (Carb version) and I'm having a little trouble starting it. Narrowed it down to either the Starter Motor and / or Battery Cables.

I've read that battery cables should be the same length, even if one needs to be loosely looped. My Positive cable is 3m in length and the Negative is only 1m in length. Both are AWG 2 size and look original (with some signs of corrosion inside).

Is the above a standard setup? (As the lengths are different and the AWG 2 is right on the limit for that length of run and amps needed).

I'm considering upgrading the cables to AWG 0, just to rule that out the cables as an issue, before moving on to replacing the Starter Motor. Unless the above is a normal setup??

Thanks

James
 
Last edited:
_jp said:
Hi all,

My Maxum 1800 SR3 has a Mercruiser 4.3L (Carb version) and I'm having a little trouble starting it. Narrowed it down to either the Starter Motor and / or Battery Cables.

I've read that battery cables should be the same length, even if one needs to be loosely looped. My Positive cable is 3m in length and the Negative is only 1m in length. Both are AWG 2 size and look original (with some signs of corrosion inside).

Is the above a standard setup? (As the lengths are different and the AWG 2 is right on the limit for that length of run and amps needed).

I'm considering upgrading the cables to AGW 0, just to rule that out the cables as an issue, before moving on to replacing the Starter Motor. Unless the above is a normal setup??

Thanks

James
Click to expand...

Is it cranking slowly, or taking a long time to start with normal cranking speed?

You should be able to have the starter tested by a decent shop that specializes in automotive electrical work.

You can do a voltage drop test to find out if the cables are at fault, but it's also a good idea to check for areas that are more stiff than others- bend the cable in the middle and work your way to both ends- you'll see where it doesn't want to bend and if that's true, they're damaged inside of the insulation.

Not to overstate the obvious:

- Clean and tighten the battery cable ends. If the cables haev ring terminals, make sure the starter wire is at the bottom of the stack if more than one wire is connected to the stud.
- Clean and tighten the ends at the solenoid and ground on the block.
- Measure voltage drop across the solenoid- if the battery has been discharged to the point where it cranks slowly or stops cranking and/or you have needed to crank it for a long time, the contacts can be damaged by heat.
- Have the battery tested.

www.smartautotraining.com

Voltage Drop Test Explained

Learn how a voltage drop test helps diagnose electrical problems, saves money, and improves accuracy in automotive repair.
www.smartautotraining.com www.smartautotraining.com
 
jimn said:
Is it cranking slowly, or taking a long time to start with normal cranking speed?

You should be able to have the starter tested by a decent shop that specializes in automotive electrical work.

You can do a voltage drop test to find out if the cables are at fault, but it's also a good idea to check for areas that are more stiff than others- bend the cable in the middle and work your way to both ends- you'll see where it doesn't want to bend and if that's true, they're damaged inside of the insulation.

Not to overstate the obvious:

- Clean and tighten the battery cable ends. If the cables haev ring terminals, make sure the starter wire is at the bottom of the stack if more than one wire is connected to the stud.
- Clean and tighten the ends at the solenoid and ground on the block.
- Measure voltage drop across the solenoid- if the battery has been discharged to the point where it cranks slowly or stops cranking and/or you have needed to crank it for a long time, the contacts can be damaged by heat.
- Have the battery tested.

www.smartautotraining.com

Voltage Drop Test Explained

Learn how a voltage drop test helps diagnose electrical problems, saves money, and improves accuracy in automotive repair.
www.smartautotraining.com www.smartautotraining.com
Click to expand...
It's a bit intermittent, sometimes it cranks, some times it clicks and then the electrics die. Wait a while, then you can attempt to turn it over again - the amps are causing heat. It's a brand new battery and I cleaned all the terminals and ground lug on the block, etc. Only thing I haven't done yet is a voltage drop test.

I have another thread on that issue, this was more to check the Sizing and Lengths of the cables, as i'm just going to replace/upgrade them. Checking before I order as they're not particularly cheap per meter when you get to AWG 0 size.

I appreciate the input and the video link, thanks
 
the length of each cable doesn't have to be the same. The length and size are selected by the rigging shop when the hull is built and should be consistent with the engine maker's installation specs. Going up one size only hurts your wallet. The biggest thing is to get marine grade cables and not the auto grade cables...big difference there...
 
_jp said:
It's a bit intermittent, sometimes it cranks, some times it clicks and then the electrics die. Wait a while, then you can attempt to turn it over again - the amps are causing heat. It's a brand new battery and I cleaned all the terminals and ground lug on the block, etc. Only thing I haven't done yet is a voltage drop test.

I have another thread on that issue, this was more to check the Sizing and Lengths of the cables, as i'm just going to replace/upgrade them. Checking before I order as they're not particularly cheap per meter when you get to AWG 0 size.

I appreciate the input and the video link, thanks
Click to expand...
If it's intermittent, do a wiggle test.

Best to only create one thread.

Can you post a photo of the starter- the old style didn't use gear reduction and the new ones do- they need less current, although they still need a lot. Do you have jumper cables? You can use those to bypass the existing cables. If it cranks reliably, it would point to one/both cables. Connect one and try it, then the other, individually- that isolates the + and negative as the cause.
 
makomark said:
the length of each cable doesn't have to be the same. The length and size are selected by the rigging shop when the hull is built and should be consistent with the engine maker's installation specs. Going up one size only hurts your wallet. The biggest thing is to get marine grade cables and not the auto grade cables...big difference there...
Click to expand...
Thanks for clearing that up. I've seen multiple sources contradicting themselves and found myself going down a rabbit hole. I'm going to replace with fresh cables and i'll go up one size for good measure. Thanks
 
Last edited:
jimn said:
If it's intermittent, do a wiggle test.

Best to only create one thread.

Can you post a photo of the starter- the old style didn't use gear reduction and the new ones do- they need less current, although they still need a lot. Do you have jumper cables? You can use those to bypass the existing cables. If it cranks reliably, it would point to one/both cables. Connect one and try it, then the other, individually- that isolates the + and negative as the cause.
Click to expand...
I think it's the original starter (2006 ish). I was going to replace it with an OEM one rather than an aftermarket. Do the newer OEM ones use the gear reduction do you know?

Jumper cables got it turning over, after I had spent some time on it. Then it would turn over without them.

Note taken regarding the thread🫡 This thread was mainly to resolve my battery cable length and size questions, rather than diagnose the starting, was unsure if I should separate it or not? If admin are able to combine it, please feel free to do so. Thanks
 
Do you understand how the system works?
Power from the key goes to the "slave solenoid" first .It is a low current relay that operates the solenoid on the starter, that connects the large contacts in the solenoid to spin the starter.
4,2,o,oo,welding cable doesent matter the length ,,clean connections matter, A battery cable going bad from internal corrosion usually has a bulge at the corroded area.
 
 
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