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MG MGB GT V8 Factory Originals Technical - Starter Motor problem

I'm having problems starting at the moment. I've been driving my V8 conversion irregularly recently (once every 10 days to 2 weeks) and as a result often have to jump start with a portable booster pack as the battery has drained. This is normally fine, and once the battery has recharged itself, the car starts ok by itself (without assistance).

Yesterday I performed the same routine, but even after the battery was fully charged (I checked this with a voltmeter) the starter motor was still chattering and failed to start the engine when I stopped and tried to restart. Using the booster pack solved the problem, but made me wonder if the problem is now the solenoid on the starter motor rather than a drained battery, although I'm confused that it still starts with help from the battery pack.

Any thoughts welcome.

Thanks, Chris.
Chris Holmes


There's probably nothing wrong with your starter. Try using one of the battery management systems. I use the one sold by Carcoon, 35, but there may be others out there. Just leave it permanently hooked up to your battery remembering to disconnect before you drive away! Very easy to install and you have a full charge every time you want to use the car. I had exactly the same symptoms as you describe and this cured it.

David Canning

Chris, you cannot check a lead acid battery with a voltmeter ! Even if the battery is practically dead, it will still show 12V. A hydrometer or a tester that checks the battery under load is the only way. Barrie E
Barrie Egerton


As a battery gets older it holds less and less charge and seem to deterorate with infrequent use. Starting a car from cold particularly when it hasn't been started for a couple of weeks takes a lot more out of the battery than a car with a warm engine. I guess you have reached the point where your battery can't even do a warm start! That means a new battery. The idea of a "ttickle charger" is a good one and will ensure your new battery is in top condition even if you don't use the car for a couple of months.

R Weston

As David says if it starts with a jump then it is nothing to do with the starter, solenoid, starter relay etc. but the battery. Either the alternator isn't charging the battery, something is discharging it while parked, or the battery is knackered and it isn't holding a charge.

The first is easy to check - you should see about 14.5v on the brown at the fusebox with the engine running at a fast idle with minimal electrical load. With all factory electrics switched on you should still see 13v or better.

Do you have an alarm fitted? I found mine (set or not, although setting it takes more current) would discharge the battery enough to prevent it starting if not run for 2 weeks. This was on a battery less than 18 months old. After the 2nd replacement when the garage said they weren't prepared to replace it anymore, and now the car is usually parked in a garage rather than in the open, I fitted a battery cut-off switch and now it really whizzes the engine over after a month or more. Without an alarm, or anything else that needs a permanent 12v supply (like a clock or radio which should be minimal anyway) my roadster can go for a couple of months and still start with only slightly less cranking speed with normal. If you don't have an alarm check for a drain by removing the battery ground strap and connecting an analogue voltmeter on its 12v scale in its place. Without clock, radio, alarm etc. or anything else that needsa a permamant 12v supply you should see just a few volts registered. This is the normal leakage current of the alternator diodes which is microscopic and can be ignored. If you see a full 12v registered you have a drain. Remove the alternator plug to eliminate that, and if still shown remove the purple and hazard flasher (if fitted) fuses. If still shown you will have to start disconencting browns from the ignition switch, main lighting switch, starter and ignition (if fitted) relays, and lastly the starter solenoid, to try and isolate it.

If you have an alarm, don't want to fit a battery cutoff switch, and it is convenient to use a charger, then fit a cigar lighter plug to the leads which will make it a doddle to plug in and out, and I defy anyone to forget to remove it before they drive away.

In my experience a *digital* voltmeter *will* show a partially discharged battery off-load, just a few tenths tenths difference is enough to see. And *any* voltmeter will show a partially discharged battery if it is under load. Whilst an off-load battery only shows a very slight reduction in voltage until it is really flat an on-load battery shows a much more linear reduction in voltage.

The solenoid chattering with a fully charged battery indicates either bad connections between the battery posts and the solenoid, the starter relay and the solenoid, or the motor is on the way out, which is a 'common' occurence on V8s.
Paul Hunt

This thread was discussed between 21/07/2004 and 23/07/2004

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