Slow starting when warm

[Robb]

This has got me a little confused, when I start my car from cold she fires into life first turn of the key, first time every time.

However once you have been for a run, turned off the engine and then go to start again it can be very sluggish and slow to start.

Sometimes it will even sound like the battery is almost flat and the starter will go very slow, other times it will just take a bit of turning over before it fires.

Either way it always starts, Im just a little confused what is causing the problem.

I have recently replaced the plugs, I could replace the starter, but Im not sure it would fix it as why would it start so well from cold but not hot?

Any ideas Thanks

[Baron VonZeppelin]

Heat brings out and compounds the weaknesses in high load electricals like the things involved with cranking our diesels.

If not already done this, go through and clean all connections from battery to starter - and all grounds.

Testing ohms on battery cables, and various voltage drop tests, will usually find the culprit.

Check out this similar thread and follow some of those links/suggestions.
http://www.vwdiesel.net/forum/index.php?topic=26568.0

[rs899]

I had that problem and found out I had a very bad ground at the battery terminal.  I swapped on a very nice ground wire from a MK3 and now it spins much faster.  It still doesn't start as quickly hot as cold (Florida cold), but I think the remaining issue is that the IP and fuel is hot and not developing as much pressure.

[westcoaster]

I think I have a similar issue.

Run some place and turn off the engine. Return 5-10 minutes later and crank. It won't fire immediatly. I'll have to crank quite a bit to get it to fire.

What I have found is crank (ie: the duration of a telephone ring)... if it doesn't fire immediatley I stop cranking then promptly bump the starter again and it usually immediatly fires.

Don't know why but there is something about the crank, stop, crank that seems to make it fire faster than simply cranking. Time wise it may take longer but it's less time on the starter...

[vdubspeed]

add me to the list. Starts fine when cold. Hates to be hot restarted.

I thought hot restarts would be the easiest thing for a diesel. I have AWESOME grounds and a 1000ca optima battery.

My fuel solenoid has the voltage too.

Just takes a little longer when hot.

[wolf_walker]

Tired pumps I would guess, add a low pressure inline pump and experiment. 
Wonder if the delivery valves could be leaking down and taking an extra pump or two to
get the pressure in the line up again?  The inline pump wouldn't help that, but del valves are
pretty cheap.  Mine is a little slow to catch when heatsoaked, but not really noticeable unless you
know the thing pretty well.  I know my pump is tired, well over 300K on it.

[westcoaster]

My pump is probably not that far behind yours...

It had 390,000 km with a non functioning speedo/odo when I got it...

No leaks, so it may have been rebuilt at some point in it's past life.

[burn_your_money]

If it push starts easy when hot I would highly suspect a voltage drop problem. The DIY is in the FAQ

[Robb]

I will park the car on a steep hill when warm and see if it will push start first time. If so I will refer to that DIY section.

Thank You

[regcheeseman]

BLUE and WHITE wire on the temp sender on the front of the head....disconnect it. Your hot/warm start problems will be gone.

It'll invoke the glow plugs regardless of engine temp - I get in, give two secs of glow and the hit the starter - instant fire!

They are some blinkered people on here that don't like this 100% solution because it uses the glow plugs.

What would you rather? A couple of seconds of glow plugs or sat there like a lemon cranking the motor over and over and over - wrecking your starter motor and your cool.

I've done this mod to LOTS of cars, advised many others and received only positive feedback, my current project car has a bespoke loom; I didn't even bother to include this wire.

Of course if you do it and are not happy - just reconnect the wire. 

[Robb]

If this works I will be a very happy man mate!

Really hope it does.

Thanks

[regcheeseman]

If this works I will be a very happy man mate!

Ironically, your the only poster on this thread that this tip wont help. Your slow starter motor is indicative of another issue - posssibly earth related, or starter motor related.

Sorry.

However it may well improve your chances of it actually starting with a sluggish starter motor

[blackdogvan]

I experienced this exact issue on my AAZ. While tricking your glow plugs will work in my case it was a slow starter that was to blame for the warm start issue. I'd start by cleaning the mounting face and terminal connections on your starter. GP's have a life & hitting them all the time needlessly for the sake of a dirty ground path on your starter isn't a great solution.

[Robb]

Tried your method today Reg and it worked a treat car now fires up first time even when warm, I only let the plugs heat for a second or two when I know the car is warm as to not wear out the plugs any faster that necessary, however Im pretty sure this method is less harmful in the long run as not having to turn the starter over and over to get the old girl firing must be a good thing.

With this is mind that she now fires off straight away with the extra blip of the heaters when warm, what would that indicate the problem is that stops her firing without the plugs?

Now I just have to find the solution as to why the starter motor sounds a little sluggish, even though shes now firing first time I still dont think the starter is quite as good as it could be. Will clean it and look at earths and such first and if that doesnt resolve the issue will replace the starter and go from there.

Any help anyone has as to what this method of using the plugs all the time would indicate is the problem please let me know.

Thank You

[regcheeseman]

Tried your method today Reg and it worked a treat car now fires up first time even when warm,

Funny that! Everyone who ACTUALLY tries it has the same result!

The reasons? Possibly

faulty glow plug relay / temp sender  meaning the plugs don't come on when the maybe should

worn engine

poorly set timing

slow cranking speed

Or a combination of all of them?