Cranking to build oil pressure

Belfry

Junior Member
Messages
72
My QPV has been dormant for several months. I'd like to crank the engine over a couple of times before starting it.

My DB9 has the facility to do this, does anyone know if this can be done on a QPV (zf auto)?
 

Gazcw

Member
Messages
1,547
The Aston is accelerator fully depressed. There are a few other Manufacturers that do this too. Cannot remember which though. I might try it later.
 

CatmanV2

Member
Messages
34,510
Hmm, there are.

Well F14 under the bonnet is fuel pump relay but F63 in the boot is the actual pumps which is probably simpler.

But really? Is it worth it? How much wear do you think you're going to save by turning it on the starter and building pressure rather than turning it by burning fuel to build pressure?

C
 

eight

Junior Member
Messages
59
The Aston is accelerator fully depressed. There are a few other Manufacturers that do this too. Cannot remember which though. I might try it later.
That's clever but could do more harm than good if the manufacturer didn't set it like that. Zero to rev limiter from stone cold o_O
 

Belfry

Junior Member
Messages
72
Hmm, there are.

Well F14 under the bonnet is fuel pump relay but F63 in the boot is the actual pumps which is probably simpler.

But really? Is it worth it? How much wear do you think you're going to save by turning it on the starter and building pressure rather than turning it by burning fuel to build pressure?

C
Thanks again. I'm only really doing it because Aston recommends it on their cars after a long period of rest. I will try it now. Haven't started the car since April
 

CatmanV2

Member
Messages
34,510
Thanks again. I'm only really doing it because Aston recommends it on their cars after a long period of rest. I will try it now. Haven't started the car since April
You have to wonder if that was an engineer or a marketeer that made that recommendation.....

Your car though, so, <shrug>

C
 

safrane

Member
Messages
13,194
Not an engineer or mechanic, but with a mechanical oil pump is the flow and pressure not dictated by RPM?

So the crank will rotate as many times, regardless of spark/combustion... but one may push unburnt fuel and a little oil into the exhaust system?
 

Zep

Moderator
Messages
4,180
Imagine things like a camshaft. If it opens a valve that is held closed by a spring 70 times a minute on the starter or 2000 times a minute with the blip at startup. So if it takes 10 seconds of cranking to build the pressure the engine turns over 10 times to achieve this. If it takes 2 seconds for the pressure to build when started normally that is around 70 revolutions. If there was little or no oil film on something like the cam, the additional pressure and speed will induce more wear. Also you have the benefit of being able to control the engine speed until you know there is pressure.

If, as I have been advised, you disconnect the injectors rather than pulling pump fuses, no fuel passes through.

It is very much a personally choice though.
 

Belfry

Junior Member
Messages
72
I watched a video from Bamford Rose, the Aston Martin specialist, in which they said that they did not recommend starting a car that had been sitting for a while without using this procedure.

Maybe I was being over cautious ( or just bored). Maybe there is a difference between the Aston V8s and V12s when compared to the Maserati V8?

Either way, it worked and I have just been for a drive without the engine exploding!
 

CatmanV2

Member
Messages
34,510
I watched a video from Bamford Rose, the Aston Martin specialist, in which they said that they did not recommend starting a car that had been sitting for a while without using this procedure.

Maybe I was being over cautious ( or just bored). Maybe there is a difference between the Aston V8s and V12s when compared to the Maserati V8?

Either way, it worked and I have just been for a drive without the engine exploding!
Well that's a win in anyone's book :)

C
 

hashluck

Member
Messages
793
Just to be clear with the Aston you do not start the car with your foot flat to the floor, you just crank it. The start is inhibited by flooring the accelerator past kickdown. AFAIK this only applied to early and automatic DB9s - I think Aston removed the feature as it was just too confusing for owners. See attached in any case.

73366
 

Geo

Member
Messages
434
I suspect the pre-pressurisation is more to do with filling the hydraulic tappets than anything else.
 

TimR

Member
Messages
1,523
From experience, whenever Ive cranked sans fuel relay to build pressure, the motor burns oil that clearly makes it past valve guide/stem seals in the upper comb' chamber...
 

TimR

Member
Messages
1,523
The point here is that oil pressure is designed to be present via the one way valve & pressurised oil bag. If it isn’t, something isn’t doing what it’s meant to; 6 month, winter stand overs aside perhaps...