400a "mega" fuse for starter keeps blowing
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1st Gear
Joined: Mar 2020
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400a "mega" fuse for starter keeps blowing
Every once in a while, I blow my 400A mega fuse when trying to start my 2010 RR HSE 5.0.
The first time it happened (just a week after I bought it in February of this year), I assumed my starter was bad and replaced it. Still didn't crank, so I freaked out and then found the big mega fuse hanging off the battery and realized it was blown.
Usually, once I dig up a new fuse and put it in there, it will crank, but the first revolution of the engine is VERY slow/hard. It has the cadence of a dying battery for a second, then speeds up and starts and runs fine. The battery is new and tests fine. Alternator is also good as far as I can tell.
Other clues:
My theory is that my coolant leak is through the head gasket and into one or more of the cylinders. When normally running, the leak(s) are not bad enough to cause noticeably poor running of the engine. But when I shut off a hot engine, residual pressure in the coolant system drives coolant into one or more cylinders. Then, when I try to start it the next time, the cylinder(s) is/are partially hydro-locked, causing the hard cranking. After the first revolution, the valve(s) in the stuck cylinders open and release the accumulated water and the engine runs mostly fine.
My biggest question is whether it's realistic that the head gasket could be leaking into 6 cylinders at once to cause the codes in those cylinders. Seems crazy. Or would a leak and coolant accumulation into a single or pair of cylinders potentially cause misfire codes in several other cylinders as well?
Does this sound likely to you? Any other ideas?
Thanks in advance,
Donnie
The first time it happened (just a week after I bought it in February of this year), I assumed my starter was bad and replaced it. Still didn't crank, so I freaked out and then found the big mega fuse hanging off the battery and realized it was blown.
Usually, once I dig up a new fuse and put it in there, it will crank, but the first revolution of the engine is VERY slow/hard. It has the cadence of a dying battery for a second, then speeds up and starts and runs fine. The battery is new and tests fine. Alternator is also good as far as I can tell.
Other clues:
- I have a slow coolant leak somewhere. Need to add about 2 cups of water/coolant for every couple of hours the engine runs.
- Coolant does not make its way to the ground, ever.
- I sometimes get random misfire codes in cylinders 1-6, a well as the "misfires in the first few seconds" code
My theory is that my coolant leak is through the head gasket and into one or more of the cylinders. When normally running, the leak(s) are not bad enough to cause noticeably poor running of the engine. But when I shut off a hot engine, residual pressure in the coolant system drives coolant into one or more cylinders. Then, when I try to start it the next time, the cylinder(s) is/are partially hydro-locked, causing the hard cranking. After the first revolution, the valve(s) in the stuck cylinders open and release the accumulated water and the engine runs mostly fine.
My biggest question is whether it's realistic that the head gasket could be leaking into 6 cylinders at once to cause the codes in those cylinders. Seems crazy. Or would a leak and coolant accumulation into a single or pair of cylinders potentially cause misfire codes in several other cylinders as well?
Does this sound likely to you? Any other ideas?
Thanks in advance,
Donnie
1st Gear
Joined: Aug 2023
Posts: 1
Likes: 0
Every once in a while, I blow my 400A mega fuse when trying to start my 2010 RR HSE 5.0.
The first time it happened (just a week after I bought it in February of this year), I assumed my starter was bad and replaced it. Still didn't crank, so I freaked out and then found the big mega fuse hanging off the battery and realized it was blown.
Usually, once I dig up a new fuse and put it in there, it will crank, but the first revolution of the engine is VERY slow/hard. It has the cadence of a dying battery for a second, then speeds up and starts and runs fine. The battery is new and tests fine. Alternator is also good as far as I can tell.
Other clues:
My theory is that my coolant leak is through the head gasket and into one or more of the cylinders. When normally running, the leak(s) are not bad enough to cause noticeably poor running of the engine. But when I shut off a hot engine, residual pressure in the coolant system drives coolant into one or more cylinders. Then, when I try to start it the next time, the cylinder(s) is/are partially hydro-locked, causing the hard cranking. After the first revolution, the valve(s) in the stuck cylinders open and release the accumulated water and the engine runs mostly fine.
My biggest question is whether it's realistic that the head gasket could be leaking into 6 cylinders at once to cause the codes in those cylinders. Seems crazy. Or would a leak and coolant accumulation into a single or pair of cylinders potentially cause misfire codes in several other cylinders as well?
Does this sound likely to you? Any other ideas?
Thanks in advance,
Donnie
The first time it happened (just a week after I bought it in February of this year), I assumed my starter was bad and replaced it. Still didn't crank, so I freaked out and then found the big mega fuse hanging off the battery and realized it was blown.
Usually, once I dig up a new fuse and put it in there, it will crank, but the first revolution of the engine is VERY slow/hard. It has the cadence of a dying battery for a second, then speeds up and starts and runs fine. The battery is new and tests fine. Alternator is also good as far as I can tell.
Other clues:
- I have a slow coolant leak somewhere. Need to add about 2 cups of water/coolant for every couple of hours the engine runs.
- Coolant does not make its way to the ground, ever.
- I sometimes get random misfire codes in cylinders 1-6, a well as the "misfires in the first few seconds" code
My theory is that my coolant leak is through the head gasket and into one or more of the cylinders. When normally running, the leak(s) are not bad enough to cause noticeably poor running of the engine. But when I shut off a hot engine, residual pressure in the coolant system drives coolant into one or more cylinders. Then, when I try to start it the next time, the cylinder(s) is/are partially hydro-locked, causing the hard cranking. After the first revolution, the valve(s) in the stuck cylinders open and release the accumulated water and the engine runs mostly fine.
My biggest question is whether it's realistic that the head gasket could be leaking into 6 cylinders at once to cause the codes in those cylinders. Seems crazy. Or would a leak and coolant accumulation into a single or pair of cylinders potentially cause misfire codes in several other cylinders as well?
Does this sound likely to you? Any other ideas?
Thanks in advance,
Donnie
Did you found it to be the Head Gasket? My 2010 RR HSE 5.0 V8 is doing the same as you stated.
Please let me know what came out to be i. Your case.
Thanks
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