geschwindig

I would disagree with Dave's opinion on the 5 second cranking without letting the engine start. Most of the damage from lack of lubrication in an
ohc engine is in the valve train, which is why you use some moly or oil to coat the cam bearing surfaces and lifters when you rebuild it.
Cranking for a few seconds over and over just lets the oil drain back over and over so it never gets to the top end. Once the engine starts the oil
pump gets the oil up there very quickly minimizing the metal to condition very quickly. Maybe if you have 60w motorcycle oil in the car, or some
goofy viscosity enhancer, you would have more chance of damage, but with the correct oil for the engine in the ambient temp it is in, there
would be less chance of excessive wear by just starting and letting it run. The sooner the oil is there, the better, IMHO. And like Colin said, let it
run for a while at normal temps, not just a few minutes.
(Make sure the garage door is open, of course....).

Just my $0.928. Maybe Greg can chime in on this one and set us all
straight...

Kevin

MJ Ireland

But Dave's point is that by doing what he said you build oil pressure at the relatively low revs of engine cranking then starting the engine, as opposed to starting and running at a 1,000 rpm for a few seconds with low oil pressure.

So the argument is that with the engine 'primed' and oil pressure built and oil circulated it will likely/may lead to less wear on startup.

worf928

This. Exactly.

I agree.

The assumption above is that there is any oil to 'drain back'. Based upon my observations of the 928 this assumption is not valid once the engine has been sitting for more than about two weeks. I've watched many 928 oil pressure gauges on start-up many times under many conditions. There is a big difference in how long it takes the oil pressure gauge to register pressure depending upon how long the engine has sat. If it's sat for a few minutes, hours, or even a week-ish, the gauge will begin registering pressure within a small fraction of a second of the engine starting. If the engine has been sitting for several weeks it can take a few seconds to begin registering pressure.

The pressure sender is right next to the pump. If the gauge is not registering pressure (and is hooked up, working, etc.) then the pump is still busy building a vacuum to the sump to draw oil. Obviously a worn pump will take longer to suck up oil than a new pump. But, that's in the margin in this context.

Absolutely. But, the point of the above is that when there is no oil film from the pump down to the pickup because the engine has been sitting, it can take seconds for oil to get to the pump. Once it does get to the pump, then of course, it will get to the heads in a fraction of a second.

During cranking the engine is turning at roughly 100 rpm. At that speed there isn't enough heat from friction to cause wear quickly. (Although, you are causing undo wear on the starter. Of course a starter is easier to replace than main bearings...) But, once the engine ticks over to 1100-rpm shop-cold idle, heat on surfaces with no or little oil film will build very, very quickly.

I for one do not like to see any engine in my garage run for two seconds with no oil pressure.

Right. And I believe that when the engine has been sitting over-winter, that priming the pump gets oil exiting the pump under pressure two seconds faster than it otherwise would.

I agree. Once you've started the engine (using whatever SOP you prefer) most of the start-up wear has happened. Then you want the engine to run long enough to expel moisture and other volatiles that have been entrained in the oil.


Yup. I'd love to get Greg's opinion.

Just in case it's not clear:, I only do the 'priming' when an engine has been sitting for several weeks (or after an oil pan gasket job), not every time the motor is started. Under normal conditions where the engine hasn't been sitting for a couple of weeks it's not an issue.

geschwindig

Dave, you're probably right. Looking at the flow diagram I can see where a
worn pump could delay oil to the main gallery quite a bit in a dormant motor.
Point taken. I think the plain main bearings handle the friction much
better than the no bearing top end, however, and get pressurized oil faster
either way. We may be splitting hairs.

I'm using 15/50 synthetic and the guage shows pressure within a second,
even after a couple weeks of sitting. I remember my 79 being about the
same. Of course in SoCal the car rarely sees temps below 40F. You probably
have much more experience with these motors than I. Might be interesting
to find some factory info on this. Thanks for your explanation.

LostInSpace

It's not just the salt, the roadside verge's here often run down towards the road i.e. they're higher, so you get a lot of runoff, which brings mud, dirt, etc into the salt & water mix - cars get filthy.

Local news this morning advised it's the wettest winter on record.

You guys in California don't know how good you've got it!

The Forgotten On

A state of emergency caused by a drought. Lots of fun. You could send us some of your rain

Shawn Stanford

I'm leaning that way. I'm absolutely going to a full set for my Cayenne, just waiting for the sales to start.

Bertrand Daoust

+1.
I would not start it, unless you can drive it for at least 20-30 minutes.
We cannot do that here unless driving on salty road at best. I would never do that with my car.
That way, it's a new beginning every April!