Hot Start Problem

Hi,

The starting when hot problem on the V6 continues........... Having got the local garage to fit a `new' starter (guaranteed reconditioned) to replace the old one that had been overhauled locally, the solonoid clicks loudly every time, cold or hot. Problem is that when the engine is hot, sometimes it takes a dozen or more tries before the click is accompanied by the starter motor turning the engine over. This only ever happens when the engine is good and hot. The fact that it clicks every time shows that the power supply to the solonoid is good. My guess is that, maybe due to the unit expanding in the heat, the contact breaker within the starter motor doesn't always close properly when the thing's hot. Is this a common problem with the V6 engine? I'm going to have to sort it soon; the danger is that if the contacts don't close properly, they might spark and burn up the contact faces.

Any ideas, anyone?????

Regards,

Jim.

Jim,

It's a hard one to diagnose without seeing the car but here goes:-

The best way to find the fault is to take a multimeter and set to volts. Clip the black or -ve wire to the -ve battery post (not the -ve battery connector because that might be the problem). Start by putting the red +ve lead of the meter on the +ve battery post and turn the starter. Check for 11-12v. Next move the red lead to the +ve battery terminal (the lead bit with the securing bolt) again turn the starter. Again look for 11-12v. Keep doing this moving further and further along the circuit. The next point should be the inlet terminal of the solenoid, then the outlet terminal, then the terminal on the starter motor. All of these should show 11-12v when cranking. Whenever the voltage disappears between two readings then suspect the component in between.

If all the positive side of the circuit passes the enxt thing is to check the negative side. Start by putting the red lead of the meter against the body of the starter. The starter earths through the body and hence if the earth is broken in any way then the meter should show something other than 0v. Next find the thick black cable running from the engine to either the -ve terminal of the battery or the body somewhere. Again test this point with the red lead of the meter. Any reading above zero is suspect. Finally put the red lead on the -ve battery terminal (still with the black lead on the -ve battery post) and again test for voltage.

The black lead should have been on the -ve battery post throughout all the tests.

If I was a betting man I would suggest that the earth has the highest likelyhood of being faulty. A small resistance would conduct enough current to bring in the solenoid but when trying to pass the starter current through the same resistance, the resulting voltage drop is so great that it wont turn the starter. No dip in the brightness of the dash lights when starting would support this theory. Try the big black cable where it connects to the engine block and at the other end where it connects to the battery or body.

Need more feedback from experiments like this to narrow down the possible cause.

Hope this helps.

cheers

noz

Thanks Noz,

Problem is that this only happens when the engine is good and hot; would an earthing problem or a +12 volt problem be so temperature sensitive? What you're suggesting about checking the +12 volt supply down the line stage by stage to both the solenoid and the starter motor makes sense; problem is that the starter is so well buried that none of the connections on the starter body or the solenoid are accessible from above. They could be perhaps from underneath, but having collapsed one of a pair of ramps and later the original manufacturers jack simply by the weight of the car, I need it well supported over an inspection pit or preferably on a lift before I'm getting under the thing.

Logic ain't my strong point, but my reasoning is thus. When I turn the key I get a loud click from the solenoid every time with the engine hot or cold, so the 12 volt positive feed to the solenoid via the ignition switch, inhibitor switch on the gear selector and lockout relay on the security system along with the under bonnet relay are all ok. If this car's the same as everything else I've come across, the 12 volt positive feed for the starter motor comes direct from the battery to one side of a switch operated by the solenoid. When the solenoid energizes, it pushes one end of a pivoted lever, the other end of which throws the starter motor pinion into mesh with the ring gear on the flywheel. As the lever reaches the end of its travel it closes the switch and allows +12 volts onto the starter motor. As the motor only goes wrong when it's hot, whatever causes the problem has got to be temperature sensitive.

In practice, hot or cold when the starter motor works it spins quickly; even if I have to turn the key a dozen times or more, (each time getting a good loud click), when the motor eventually works I never get the kind of slow `chug' that would indicate a flat battery, or high resistance in the + or - feed to the motor so I'm thinking that the feed to the starter motor switch is ok. Panel lights dim when the key is turned whether the starter motor turns or not, however the solenoid itself draws a lot of current when it operates, probably enough to drop the voltage on the panel lights. My thoughts are that the fault has to be failure of the +12 volt supply to the starter motor, with the solenoid operated switch being the most likely culprit.

I can't see any practical way of testing the starter motor in circuit as by the time the car's up on the lift round the local garage and the heat shields been removed and the contacts exposed, the engine will have started to cool down anyway. My thoughts are that the starter motor has to come off and the switch contacts moved forward enough so that when the solenoid is energized, the switch closes a bit earlier.

I've just (this evening) come across another rather nasty problem which could maybe be a symptom of a blown head gasket. I'll post this separately; hope it's not terminal.

Happy daze,

Jim.