engine Throttle use and engine wear

[TR5tar]

Reading threads relating to hot starting and cold starting procedures got me thinking. My car sparks into life without too much effort at all when it's warm - no choke and no throttle. However, as expected, when cold it takes a little longer to get going. I always go for full choke, but what I do with the throttle is not always the same. If I give it a little throttle and feather as I crank, it slowly comes to life with a bit of shaking and rattling, but with a bit more throttle it gets going faster.

 

I appreciate that how well a car starts and how quickly it gets to a smooth tick-over will depend on a number of things, but what I'm wondering in general is: What will cause more engine wear - less or more throttle at start up?

 

Darren

Edited July 9, 2015 by TR5tar

[ctc77965o]

I guess you are injected so the throttle position is controlling the squirt volume - more thottle=more fuel=quicker start (I see same on BMW2002Tii).

For carb cars the same discussion runs with mechanical versus electric fuel pump...the mechanical pump only primes the carbs once the engine is turning, giving time to build oil pressure before the engine fires. Electric Pump pre-primes the carbs so the car starts earlier.

 

Is that ~5 second difference a factor in engine wear overall?? I would guess its a tiny proportion of total engine-wear factors.

[littlejim]

In the old days they used to advise that more fuel at the start (throttle) would wash oil off the cylinder bore during start up before the oil pump got its act going.

Thus more wear.

have no idea if anyone actually measured the results of the different techniques or whether it was a WAG.

[Dick]

I guess you are injected so the throttle position is controlling the squirt volume - more thottle=more fuel=quicker start (I see same on BMW2002Tii).

For carb cars the same discussion runs with mechanical versus electric fuel pump...the mechanical pump only primes the carbs once the engine is turning, giving time to build oil pressure before the engine fires. Electric Pump pre-primes the carbs so the car starts earlier.

 

Is that ~5 second difference a factor in engine wear overall?? I would guess its a tiny proportion of total engine-wear factors.

 

I like your broken crankshaft........I had one too.....perhaps we should start the "broken crank club"

[ctc77965o]

http://cranksnappers.blogspot.com/

 

Looks not that popular!!

[Peter Cobbold]

In the old days they used to advise that more fuel at the start (throttle) would wash oil off the cylinder bore during start up before the oil pump got its act going.

Thus more wear.

have no idea if anyone actually measured the results of the different techniques or whether it was a WAG.

Real-time measurements. They make rings or cylinders labelled with radioactive iron isotope and measure the radioactivity appearing in the oil.

They were doing it 50 years ago.

Peter

[TR5tar]

I guess you are injected so the throttle position is controlling the squirt volume - more thottle=more fuel=quicker start (I see same on BMW2002Tii).

For carb cars the same discussion runs with mechanical versus electric fuel pump...the mechanical pump only primes the carbs once the engine is turning, giving time to build oil pressure before the engine fires. Electric Pump pre-primes the carbs so the car starts earlier.

 

Is that ~5 second difference a factor in engine wear overall?? I would guess its a tiny proportion of total engine-wear factors.

 

Hi Dave,

 

Yes, should have said, TR5 PI. As you say, if I give it more throttle when cold starting it fires up more quickly. However, in the back of my mind, as Jim says, I'd always thought that it's best to go lightly on the throttle when starting and coming up to temperature. Once I've got the engine running I tend to let it warm up a bit before giving it any throttle, which is why I was a bit worried about giving it too much throttle when turning over.

 

Cheers, Darren

[Peter Cobbold]

With PI there's no need to worry about jabbing the throttle as it doesnt have carbs' throttle pump or piston damper to wash several mls of liquid fuel down the intake with each jab.

The PI fuel enrichment 'choke' will give bigger injections even if the manifold depression is high, when cranking with throttle closed. A closed throttle will still make for a rich mixture and the low pressure helps some of the fuel evaporate. So in theory, crank with closed throttle until it fires, then catch it and blip the throttle to get oil splashing onto the cam and bores. In practise I used to blip the throttle while cranking...old habits from carb engines die hard

Peter

Edited July 11, 2015 by Peter Cobbold

[RogerH]

Hi Darren,

look on the bright side, the sooner you wear the engine out the sooner you can rebuild it.

 

Blip that throttle

 

 

Roger

[TR5tar]

With PI there's no need to worry about jabbing the throttle as it doesnt have carbs' throttle pump or piston damper to wash several mls of liquid fuel down the intake with each jab.

The PI fuel enrichment 'choke' will give bigger injections even if the manifold depression is high, when cranking with throttle closed. A closed throttle will still make for a rich mixture and the low pressure helps some of the fuel evaporate. So in theory, crank with closed throttle until it fires, then catch it and blip the throttle to get oil splashing onto the cam and bores. In practise I used to blip the throttle while cranking...old habits from carb engines die hard

Peter

 

Thanks Peter. That helps. I'd been starting with closed throttle and then catching it as it fires, but after that not blipping. I'll now blip that throttle!

 

Attending the Engine Rebuild Seminar earlier this year Roger made me realise that I'll never attempt a rebuild. There's no way I'd trust myself with it

 

Cheers, Darren