4.2 D4D - hot start issue!

[dawsieboy84]

XTR Diesel has done 149k miles and starts fine when cold but after driving for a few miles and engine is up to temp it will not restart, it will just crank and crank...

Wait two mins to let engine cool down and it fires up fine?

Tested resistance on temp sensor and it is within spec so I am at a loss!!

Any suggestions would be greatly appreciated.... it is becoming dangerous now and mechanics say they cannot find anything!!

[Doosan]

My son had the same problem and turned out to be the starter motor. It was found to be full of dust from the clutch, replaced with a new one and problem cured.

[dawsieboy84]

1 hour ago, Doosan said:

My son had the same problem and turned out to be the starter motor. It was found to be full of dust from the clutch, replaced with a new one and problem cured.

was it just when hot? mine cranks and starts thudding sounds like its a timing issue but if was timing it would run like 🤬🤬🤬🤬

[Doosan]

8 hours ago, dawsieboy84 said:

was it just when hot? mine cranks and starts thudding sounds like its a timing issue but if was timing it would run like 🤬🤬🤬🤬

In his car, it would start fine from cold but when it reached temp' and you stopped and turned off the ignition it wouldn't start again. You had to leave it for about 20 minutes and then it would start fine and keep going. When he filled up in a garage he would have to leave the engine running, Very inconvenient. 

[dawsieboy84]

people have suggested the starter but wanted to check! makes sense with clutch dust etc did not even think of that! 

[gjnorthall]

You say that the starter cranks and cranks but the important factor is that it cranks at the correct speed - if it doesn't, you reduce the chances of starting the engine. Electrical resistance increases with temperature, so if you've got increased resistance due to dirty connections etc etc - matters will be worse when under-bonnet temperatures rise. The key thing is that electrical connections associated with the starter are clean and tight - this includes Battery connections, earth to body connections, body to engine connections and starter motor connections. There was a case on this forum a few weeks ago where a starter motor was replaced but the real issue turned out to be a loose connector on an earth cable.

After high mileage a starter motor may not be at it's best due to dry bearings, dirty commutator, burnt solenoid contacts etc etc and often a motor can be revived by stripping , cleaning and lubricating (a new solenoid and set of brushes is around £30 whilst you're at it). Otherwise reconditioned starter motors are readily available  

If you're in any doubt about the condition of a starter motor - it's cheap to get and auto-electrical outlet to check the cranking speed and current flow against spec. 

[Gerg]

As G says above, I remember reading that on some diesels, if the engine doesn't exceed a pre defined cranking rpm, the value of which is held in the ECU (if the Toyota engine follows VAG practice - which it may well do), then the injectors will likely not operate.  On a cold start, this cranking rpm number might be lower, if it exists at all.  On a Skoda forum, it was suggested that this is to stop the engine accidently restarting (when hot) after an accident.

On VAG diesels, it was worked out that if the Battery was not in very good condition, cold starts were fine, but hot starts could be a problem.  In those cars replacing the Battery made a miraculous difference to hot starting, (but could just as easily be a starter problem/poor connection on your car).

I appreciate that this is a question about a Toyota diesel.  But thought this might be of use.

[gjnorthall]

If cranking speed is low then the fuel pump cannot develop sufficient pressure in order for the injectors to atomise properly. The fuel needs to be finely atomised in order to mix with the air and produce an ignitable mixture. Diesel engines need a cranking speed of at least 50% more than a petrol engine and given that the compression ratio is also 50% more than a petrol - starters, cables and batteries are far more critical on a diesel.

[dawsieboy84]

this all makes total sense! It sounds laboured both when cold and especially when hot! 

This may sound stupid but imagine a classic car with external cranking arm... it feels as though it just needs a stronger arm to spin it if that makes sense? Lol

Massive help thank you everyone! 😀