Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB GT V8 Factory Originals Technical - Correct battery???

Hello again folks!

I have a query regarding the battery on my v8. I have a single 12V battery. It's forever flat, causing me no end of inconvenience and a simple job for a lucky AA man.....

Last night, the latest AA engineer to find me insisted I have the wrong battery, hence it's not charging up properly (he considered it likely the alternator is feeding too much current for the battery), and consequently is always running flat on me.... :o(

The battery is labelled Type 063 - 12V

Any thoughts on this??


Guy Harper

Sounds like B.S. unless your battery is a gell cell. If you have a regular lead-acid battery that has gone flat several times, it could well be shot and needs replacement. Have it tested. Verify that the charging circuit gets at least 14 volts(14.3) to the battery when it is charging. If it does, check for drains.
George B.

I think the 063 may be a bit too (electrically ) small for the V8. The early ones with 2 x 6v batteries are rated at 67 Ah in the manual, and IIRC the later ones with single 12v unit are rated a bit higher, I think 72.
David Smith

> HTH too :o)

Last night, I started the car, with voltmeter in hand to measure charging circuit, I was getting a minimum reading of 13.8 V, and anything up to 17.5V when reving the engine.

Considering the battery was flat on Saturday evening, was left running for 5 minutes with the AA battery charger attached, and then driven 2 miles home (lights on), frankly, i'm amazed it started at all yesterday.

<pending further investigation.....>

Woa, 17.5V is way too high. Looks like your voltage regulator is gone. It should stay close to 14V at any rpm and under load (headlights on). I'd have the alternator checked first and repaired. Looks like the AA eng was right, you may have overcharged the battery. Might have to replace the battery anyway. Have you checked to see if there are any drains on the battery with the ignition off? Just take off the negative terminal and hook a test lamp between the terminal and the cable.

Michael Hartwig

I took the car out today, and it has become apparent that the car will start quite happily when cold, but when hot will refuse.

The garage also took a look at it today, and have suggested a fault/feature of the starter motor, is that given it's proximity to the manifolds, the solenoid in the starter is prone to pack in when engine is hot.

According to my mechanic, the extra power available from the battery, when connected to an AA charger is enough to overcome the problem. Using his multimeter, we observed no more than ~14.5V across the battery terminals, even at high revs.

He is suggesting that I get a reconditioned starter moter (@ 198), and fit heat insulating tape to the manifolds. I have observed the starter motor is fine when cold, so why should I need a new one??

Perhaps someone can enlighten me???



As others have said 17.5v is way too hgh and quite likely has wrecked the battery, but that is an alternator problem, a good alternator cannot overcharge an incorrect battery.

It is possible that the battery is too small for the application but that will cause more starting problems cold than hot.

Factory V8s are supposed to have a heatshield over the end of the starter/solenoid, is yours in place? It does get very hot round there and can cause significant wiring deterioration.

What, precisely, is happening?

Not turning over at all when hot? Turning over very slowly? Is the starter relay/solenoid chattering on cranking? Is it turning over at normal speed but not firing up?

I had a problem with relay/solenoid chattering, or sometimes just 'clonk'ing when hot that was nothing more than bad connections to the solenoid. The additional resistance when hot was just enough to stop it operating. I thought it was a problem with the starter too until I started to replace it, and found the connections just crumbled off. Remade the connections and haven't had a problem since - damn sight cheaper (and more effective) than a new starter would have been.

Paul Hunt

The car will start without any problems when cold. I think my suspicions about the battery may be ill-founded, but we'll see.... I haven't replicated the 17.5V reading since...

What is certainly happening, is that after the car has warmed up, if I stop the engine, it will not turn over at all, and much clicking comes from the starter motor.

Left for an hour or so, the car starts with no problems.

As far as I can see, there is no heat shield over the starter motor. Will investigate that tonight.


Clive Wheatley has remanufactured heat shields out of an electrically insulating material as well as heat-insulated, better than the one I had which was tin and in danger of grounding the main battery lug on the solenoid. I replaced mine at the same time as the manifolds so had reasonable access, it looks very congested with the RH in-situ. Both old and new shields had a slotted hole in the mounting bracket so in theory all that is required is to slacken the bolt mounting it to the block rather than complete removal as reinsertion would probably be a lot more difficult than tightening.

Have you tracked the 12v supply through the system when the fault is evident? If you have the OE starter you should be able to get at a copper link than feeds 12v from the solenoid to the motor, as well as the 12v input to the solenoid and the operate wires to it and the relay. What voltages do you get on each of those points?

However I have to say that I went through a whole battery (ouch!) of such tests on my own system and convinced myself that the problem was in the motor itself - until Icame to remove it and found the dodgy connections.


Paul Hunt

This thread was discussed between 23/07/2000 and 31/07/2000

MG MGB GT V8 Factory Originals Technical index

This thread is from the archive. The Live MG MGB GT V8 Factory Originals Technical BBS is active now.