MG Midget Forum

I posted this in another thread a few minutes ago but it needs its own thread.

AS A SIDE NOTE: Be very careful these days jumping cars with a modern car. I have a 2018 Buick Enclave (the wife's grandkid taxi). I used it to jump another vehicle several months ago in a Walmart parking lot because that vehicle had a dead battery. The other vehicle started just fine and we both went on our merry ways. Three days later my battery was dead. I charged the battery with my battery charger and drove it to a battery specialist because I knew the battery was 4 years old and might need replaced. They tested the battery, it was weak because of its age but otherwise should have lasted a while longer. The problem was an electrical module and the alternator. When I jump started that other vehicle there must have been a static spark that fused the module which in turn burned up my alternator rectifier. The end result was my battery wasn't being charged, thus the dead battery after a few days. The new battery, module and alternator cost me $800 to replace. MORAL OF THE STORY: don't jump start older vehicles with a newer model car. Use a battery pack to jump start cars or don't do it. The cost of the battery pack was a lot less expensive than the parts replacement.

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JMAC

Jere McSparran
JMAC Engine Shop
Website: http://www.jmacengineshop.com
email: jmacengineshop@gmail.com
Phone: 217-232-7303

Very good info, Jere. Thank you for the warning.

I wonder if it would have made a difference if your vehicle had NOT been running, or if you had given their battery a chance to charge up a little, prior to them engaging the starter?

I jump start some of my cars and motorcycles with my 2010 Ford Expedition occasionally, and (to date) have not had any issues doing it. When I start a motorcycle, I do not have the Ford running, but this is more to protect the electrical system on the bike.

Now, I have the concern that you brought up nagging me in the back of my head. Thanks a lot!!!

Steve

I have jumped my 78 MGB with my 2017 Subaru Forester many many times.
No problems at all.

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1978 MGB
When diagnosing issues related to running and stalling, always check to see if you have gas in the tank first.

Jere, sorry for your troubles. But I'm betting that you connected the jumper cables with your Buick's engine running. With modern cars that will cause problems, as you have found. Before connecting the cables make sure that everything is turned off on both vehicles, including any accessories that may be connected to a power outlet. Then connect the cables, start the vehicle with the good battery, and let it run for a few minutes. Then try to start the car with the dead battery. When it starts let it run for a few minutes, then disconnect the cables.

I carry around a battery boost pack in my car, just in case.

On MODERN CAS, even the owners Manual for these cars, say: IF it is necessary, NEVER, go Battery to Battery but POS+ Terminal to -POS +Ternim Chassis Ground to Chassis Ground. or you might be buying an alternator.

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IN ALL SUBJECTS.: For those who believe, no proof is needed. For those who don’t believe, no proof is possible.

"Strive for perfection in everything. Take the best that exists and make it better. If it doesn't exist, create it. Accept nothing nearly right or good enough"
Sir Henry Royce
co-founder of Rolls-Royce .

"I take no credit for my own, of another man's fame".
Joe Baba 2021

Out of curiosity, where on modern plasticmobiles does one find a chassis ground?

I have used the nuts on the top of the struts.

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1978 MGB
When diagnosing issues related to running and stalling, always check to see if you have gas in the tank first.

Engine block, or the point where the negative post of the battery connects to the body are likely locations.

Steve

From Post 9
> or the point where the negative post of the battery connects to the body...

That kinda gets to the crux of my question...how is such a connection different than connecting directly to the (-) post, which it seems we're not supposed to do?

You don't want to connect both cables to the battery because a tiny spark can cause an explosion. Lead acid batteries produce hydrogen gas. I once was trying to jump start an old Volkswagen Beetle and they have the battery mounted under the rear seat. I had the cables connected to the other car with the engine running and while sitting in the driver's seat of the VW so I could start it I turned around and connected the positive cable to the VW battery. As soon as I touched the negative cable to the other battery post it sparked and the battery exploded. The explosion blew the battery case in half and I got a face full of battery acid. Ran in the house and climbed in the shower with no ill effects. Then back outside to hose down the car. The headliner was a plastic material that survived the acid pretty well. I was lucky I didn't get hit in the face with the upper half of the battery case when it exploded. Connect the ground lead somewhere besides the battery!

what your trying to avoid is a spike to the ecu,so best follow above connection instructions,and switch off both vehicles before disconnecting.if not its about a 1 in 10 chance you will upset the ecu,or blow it and or alternator.

Sorry this happened to you - I was always taught to use a wind source (fan, blowing, etc) to clear the hydrogen, for that reason. But Joe's post #6 says "... Chassis Ground to Chassis Ground. or you might be buying an alternator.", and I don't see how connecting to chassis ground prevents that. Not arguing, just don't understand it electrically.

It doesn't make any sense electrically. Connecting to the ground post of the good battery with the other end of the cables not connected to anything will not cause any harm. When connecting the other end make sure everything is turned off and even then connect the ground to the chassis to avoid any spark.

MOTOR MOUNT, or something METAL on the engine block. ??? Just NOT directly to the battery terminals.

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IN ALL SUBJECTS.: For those who believe, no proof is needed. For those who don’t believe, no proof is possible.

"Strive for perfection in everything. Take the best that exists and make it better. If it doesn't exist, create it. Accept nothing nearly right or good enough"
Sir Henry Royce
co-founder of Rolls-Royce .

"I take no credit for my own, of another man's fame".
Joe Baba 2021