Looking for some pointers.

The battery in the car isn't the healthiest, so sometimes can crank a bit slowly. However I've noticed a bit of a pattern forming where it really struggles to start when hot.

For instance today it fired up perfectly happily from cold, drove for an hour and stopped at a park and ride in town. Offloaded the kid, got back in to start it and got one crank and everything dimmed out... Tried again and it started.

On the way home, fired right up from cold, 30mins of traffic to the same park and ride, and again same thing. One or two very slow cranks with every thing dimmed out. This time I tried 3 times and still it wouldn't start. Grabbed my jump box from the boot and attached that and got one slow crank then a few much faster cranks and it fired up.

What I'm not sure is if the engines simply harder to turn when hot, and my battery is just not upto it, or if maybe the starter itself gets unhappy when it's hot?!

I'd go for number 3, the starter is failing. It needs more current to turn the engine over, hence the dimming lights, so the increased current demand coupled with a battery that isn't at its best, is most likely to cause the problem. A few months ago I went to rescue one owner from a car park where his starter had failed completely. Fitted a new starter and he reckoned it spun the engine over far faster than the old one had done suggesting the old one had been getting slower over a long period.

Ive just had the exact thing on my Defender 200tdi. No rhyme or reason to it, I tried the usual battery change(nicked the one off the p38) cleaned all earth's and other connections, some days it would fire up fine, other days just a slow no start crank, try again and away she would go. Reluctantly took the starter off, pig of a job, and the brush pack was a rusty mess, armature gunked up. Couldn't quite understand why it was fine one day and no good the next or even 30 minutes later. A good clean up and it's brilliant again.

iv had this issue on other vehicles and in most cases it was bad or dirty connections, has your temps risen slightly, another sign of poor earths. do the electrical tests first before you disturb everything and then check your starter.

Thanks.

I will see if my spare engine has the starter attached and see about swapping it over.

When I bought my current P38 two years ago it had battery drain problems. Previous owner always disconnected the battery, but I wanted to fix, cleaned terminals, checked the charging etc, even bought new battery. All fixed when I replaced the starter...

th.

I am also for the starter getting tired, although mine failed from one start to another, no warning sign. Died like a true hero at over 260K km ... my friend the electrician who sorted out mentioned the brushes were totally consumed, one so much that it remained only the spring, and that is why it failed!

The next thing to consider is the crankshaft position sensor, mine did that game for two/three days: start well as cold, once it gets hot engine dies, no hot start. Replaced and never again an issue.

Gilbertd wrote:

I'd go for number 3, the starter is failing. It needs more current to turn the engine over, hence the dimming lights, so the increased current demand coupled with a battery that isn't at its best, is most likely to cause the problem. A few months ago I went to rescue one owner from a car park where his starter had failed completely. Fitted a new starter and he reckoned it spun the engine over far faster than the old one had done suggesting the old one had been getting slower over a long period.

That was me😀. I had always found it a bit reluctant to start when I filled up with E85 in France but it always started after cranking for a few seconds. I have a relatively new Hankook MF31-1000 so the battery is good. I had the engine completely rebuilt by V8 Developments & when I got it back it then seemed a bit reluctant to start when I filled up with E10 in the UK. I thought that it might free up a bit after I had run it in but eventually it just died. The new starter definitely spins the engine over much quicker. On reflection the starter had been on the way out for some months before it finally failed. As far as I am aware it was the original starter so hopefully the new Bosch one will last another twenty years or so.

A warm engine is easier to crank than a cold engine, so if it cranks easier when cold it points to something else starter motor / electrics related being negatively affected by warm temperatures.

If a starter motor is drawing more amps than usual (to dim lights etc), where is that power going (and why) if it isn't converted to magnetic power / torque to spin the engine?

Starter motor may be likely. As others have said, ensure all the main connections (positive and negative) are clean (probably not the most likely but it’s free, other than your time). My first replacement would be the battery (again, perhaps not the most likely, but you said you know it’s not the healthiest, so you’re replacing it soon anyway, so really no extra cost). But you did say you might have a spare starter, so that’s also free.

Lpgc wrote:

If a starter motor is drawing more amps than usual (to dim lights etc), where is that power going (and why) if it isn't converted to magnetic power / torque to spin the engine?

It's converted to heat. A dodgy starter has more resistance (due to the additional resistance between brushes and commutator) so it gets very hot.

Gilbertd wrote:

Lpgc wrote:

If a starter motor is drawing more amps than usual (to dim lights etc), where is that power going (and why) if it isn't converted to magnetic power / torque to spin the engine?

It's converted to heat. A dodgy starter has more resistance (due to the additional resistance between brushes and commutator) so it gets very hot.

I would agree, but the extra resistance should mean it can't draw as many amps from the battery causing the lights to dim more than usual

Lpgc wrote:

A warm engine is easier to crank than a cold engine, so if it cranks easier when cold it points to something else starter motor / electrics related being negatively affected by warm temperatures.

I wondered about this... and couldnt quite reach a conclusion...

Taken in isolation...

On a cold engine all the clearances are loose, theres probably a bit less compression as a result, certainly less friction. The oil is cold and thick, but at the point of turning the key the oil isnt really moving anyway, and it'll take a good few revolutions to get the oil pumping.

On a hot engine, everything expands, bearing and piston clearances close up, tighter ring seal, more compression, but the oil will be hot and thinner.

A hot engine typically starts easier, because theres more compression and the fuel ignites easier. However that requires the starter to be able to actually turn the engine and overcome that higher compression.

So i think i my best theory is that on balance, a hot engine is harder to crank but easier to start? IE it needs more torque from the starter to actually get it turning, but will light off easier once it is actually turning.

Not done anything with it yet, but had it out for a long drive at the weekend for a sort-of green-laning day...

1hr 30 of a/b roads, stopped at the meeting point for 30minutes. Wouldnt start, jsut a single wuuuuuuub and then nothing. Jump started fine from my spare battery. Then did some 2hours of laning, stopping at the top of a mountain for lunch. Maybe 45mins stopped, but i opened the bonnet to get some nice cooling air thru it. Started fine. Then drove down a 1000ft descent, 1st low, car didnt like that much and was billowing oil smoke by the time i got to the bottom. Shut it off for maybe 20minutes while others descended, started fine. Back up the 1000ft climb and along 15-20minutes of tracks, stopped again to wait on the rest of the cars for maybe 10minutes, and again it started fine. another 2 hours offroad, before finally stopping at a petrol station, and again, it restarted fine. So one failed start amongst half a dozen.

Really puzzling!

I had to put a new starter in my Jeep last month, it gave its last gasp as I tried to start it at the front of the queue for the Hull Ferry. I had to sit there while the whole queue drove past me onto the ship! Luckily a nice English guy who lived in Germany towed me onto the ferry and I was able to make arrangements for a recovery in Hull.
£100 for a starter and an hour on my back, really should have done that a week before!

Take it from a Canadian (our winters can get very cold). Cold engines are hard to crank. With our thinner oils these days it’s not as bad (but a lot of you folks in the UK are still using 20-50, which makes sense in your climate). In the cold, the oil gets thicker, the battery is less efficient. There may be other reasons as well, but cold engines are hard to crank.

i can remember when they started bringing out n70zz battery's , they where the biggest pain in the butt . it was a big battery for the 4wd of the day , the trouble was they killed cells in the battery, and they would play up just like you are talking about, work fine for ten starts then die, wait 10 minutes and it would go again. in this instance it was the battery. have you done the tests , if they are ok you are looking at a new battery or a starter from the sound of it .

Had a similar problem - much harder to start when (very) hot - but eventually realised it was a duff viscous fan causing it !!

The viscous fan drawing so much power that it was hard to start? I would never have believed this, partly because starting RPM is low, and I would have thought that even a direct drive fan wouldn’t have drawn much power at that low of an RPM.

Harv: Ah, no, the viscous fan was not engaging properly and so not cooling the engine properly either (but the fan still apparently rotating of course);
This was worse if the car was stationary ie. so there no good air flow over the engine. The 'excess' heat affected the starter as others stated above.
Engine started fine if left to cool for 20 minutes or so.

I see. That makes more sense.