300 Series Defender Starting problem

Hi everyone, now I think I am in the correct area.
I have a 1998 defender 300 series, short wheel base, great Landy runs like a dream.
Problem is periodically it will not start, once every 3 to 4 weeks.
I am thinking its something to do with the spider and just immobilizing itself.?
However it will all ways start if i jump it from another car or push it and jump it (need a hill)
I don't understand how it can be the security system if I can just jump start it.
Any body have any ideas? before I go completely mad.

Bob The Beast

Bob, this sounds like a tired battery or an airlock in the fuel system. Measure voltage across battery first, if possible when the old girl won't start - you should see 12.6 volts or above. When the engine is running, this should be a healthy 13.7 to 14.7 volts.

Diesel engines require a very good battery to spin it fast to start it, although they turn over ok it will not be fast enough to provide the combustion in the cylinders if a little flat.
The fact that it starts with a jumper battery after it wont start on its own, points to your battery being the problem.

v8250 said:

Bob, this sounds like a tired battery or an airlock in the fuel system. Measure voltage across battery first, if possible when the old girl won't start - you should see 12.6 volts or above. When the engine is running, this should be a healthy 13.7 to 14.7 volts.

Click to expand...

Thanks for the pointer, it seems like it was the battery.

Thanks for all the info everyone, it seems that it was indeed the Battery. done a bit of reading, a defender, 2.5 requires a battery with min 600 CCA, mine was a max of 560 CCA when new. Swapped for a larger Battery 900CCA and no problems yet.
Bob (the Beast)

Bob the beast said:

Thanks for all the info everyone, it seems that it was indeed the Battery. done a bit of reading, a defender, 2.5 requires a battery with min 600 CCA, mine was a max of 560 CCA when new. Swapped for a larger Battery 900CCA and no problems yet.
Bob (the Beast)

Click to expand...

Bob, I had a similar problem with a 200TDi. It turned out to be the starter motor solenoid return spring (normally in the "sealed" solenoid on top of the starter motor). On carefully prising the solenoid open I found the spring in 3 pieces - replaced it with a new one and it worked fine for the next 12+ years. Interestingly, symptoms were very similar to those you described - once every few weeks it just would not start.

I had similar intermittent starting problems. I gave the starting relay a little wiggle and it would start ok. I have a new relay on order.