my 76 911S is on jackstands and will be there for a while

if my memory serves, when I did an oil change, I would get about six quarts out of the sump and about six out of the resivoir, on a cold engine

when I started the car when it was cold, a lot of oil would have drained from the resivoir to the sump, a couple quarts, the oil level gauge would be around the half way, and in a few minutes it would go to the top

is this normal? I've never asked anyone else if their car does this. Mine is really high miles and is pretty worn,

so if you have six quarts of cold 20w/50 in the crank case when you start, that is a LOT of oil the scavage pump is dealing with, its taking cold, thick, oil out of the sump and pumping it to the resivoir and the only thing in between is the filter

I don't know if the oil goes to the cooler on its way to the resivoir on the scavage side, or does it go thru the cooler on its way to the oil galleries after it leaves the oil pump

the only other place where I have heard of a oil cooler blowing up with is with a friend who was desert racing a class 10 buggy. She was starting the race on a cold morning and didn't allow the engine to warm up to temp before hitting the throttle hard. Her engine builder didn't use the right spring in the oil by pass on the VW type 1

I would think a Porsche 911 would have a similar oil bypass as a VW but I have yet to tear my flat 6 down, so I don't know (someday in the not too distant future I will)

I do know some oil filters have a by pass valve so that when the filter gets too clogged up the valve opens and keeps oil (unfiltered) going to the engine, but what filters there are for the 911 with a bypass I have no idea

Otto - the gentleman who started this discussion subsequently found that he had caused his own problem - the device he was using to mount the oil filter had three openings. He blocked one, thinking it was one he wasn't going to use, and that the oil would go in another, and out the third and on its way. Unfortunately, he blocked the out fitting, which meant the oil had nowhere to go when it got through the filter. The scavange side of the pump has no pressure relief in the motor the way the pressure side does. So blammo.

Your '76 behaves like most 911s - a fair amount of oil drains into the sump when the car sits overnight or longer. Completely normal. This is why the manual specifies how to measure the oil level - get the oil up to operating temperature, let the car idle a bit on a level surface, and pull the dipstick and measure. As you have seen, if you measure when the engine is cold after the car has been sitting, the tank will read low.

If your '76 has a right front fender cooler (even if just the trombone loop), then it has an external thermostat and pressure relief to protect the front cooler system. Cold oil goes straight to the tank. If its pressure is high, there is also a pressure relief valve in the thermostat fitting which will also send it into the line to the tank, which it enters via the filter..

If you don't have the front cooler, the oil goes straight to the filter mounted on your tank

One of the virtues claimed for the Mahle (and Mann?) stock oil filters is that they, too, will bypass if the pressure is too high. So they aren't going to rupture.

I think the most important cold oil bypass in a stock motor of this vintage is the thermostat in the engine - it doesn't let oil circulate through the engine mounted oil cooler until about 180 degrees F. That way the oil warms up faster, and the cooler, which is kind of a weak length in the pressure system, isn't subjected to excess pressure. Of course, the the pressure relief pistons in the engine also help insure that the system pressure isn't too high. One keeps the maximum pressure at roughly 80 psi max, and the second opens at a rather higher pressure if something has gone haywire. So the 911s are not apt to suffer the fate or your friend in the desert.

And the 911 system is rather more robust than the VW - no tall oil cooler standing up and vibrating around. The pressure setting system on the VW is basically just like the 911's primary system. They may be the same piston diameter and case plug size. But the VW doesn't have the second system.

Lots of race motors need to warm up their oil carefully on cold days, just to be safe. I had troubles with external thermostats on mine, and eventually got rid of it. Haven't blown up anything in the oiling system in 15 or so years of this, and that oil goes through two filters and a pair of coolers before it gets to the sump tank. Though I am not using stock filters, either.

I assume ,JW, you mean mine? It's a Fram HP-4, which came with the aftermarket housing I bought. It has an internal pressure relief in the filter. Also, I have the stand piped for either full flow through the filter, or bypass. In bypass mode, most all of the oil will bypass the filter, as it is the path of least resistance.

I ran this last week, before the temps dropped into the teens, on new CAM-2 dino 10W-40. The oil was pretty slow going back to the tank, and barely went through the filter until it warmed up. I can just pull the cap off the tank, and look at it. It is like Niagra Falls when its warm.

I believe the scavenge pump makes a bit less pressure than the pressure (case circulation) pump...to an external reference. They both move the same amount of oil per unit time, else we would flood or starve the case. Relative height of the oil tank outlet is the same as the relative height of the car tank, just to try and duplicate the car condition.

I put a WIX filter on it last week, but one of my fittings started leaking from getting jostled around, and it's been too cold to go outside and work on it. The oil barely drains from the tank. I will get some pressure readings the next time I run it, and note the comparative differences between the Fram and Wix filters...the Wix has no internal bypass.

http://forums.pelicanparts.com/uploa...1359154908.jpg

Oil Movies
 

Even though the OP has long since had his questions answered, this is what cold oil ( 25F ) looks like. The second video has warmer oil, probably still not warm enough to open the thermostats. Gauge on the filter reads pressure going into the tank, after the losses from the AN-16 to AN-12 lines, and the filter.

https://www.youtube.com/watch?v=neHvgfkaS-c

https://www.youtube.com/watch?v=KO1M_xgFGaQ

Interesting. I never realised this.

So, the oil that (starts ?) to makes its way to the front cooler (even when the external t-stat is closed), that is oil that is already hot enough to have caused the engine oil t-stat to open which allowed it to flow through the engine cooler (thus preventing cold, high pressure damage to the engine cooler), yes ?

Oil is always tries to make its way to the front cooler, even when engine is dead cold at startup. The oil just gets stonewalled by the t-stat being closed on the return side. That roadblock forces the oil to take a bypass path thru the t-stat and return back to the oil tank.

You are right about the engine-mounted cooler. The oil that is hitting the external t-stat roadblock has indeed been cooled by the engine-mounted oil cooler (when the cooler is active, following the opening of the engine t-stat) and that would explain why the external t-stat opens later than the engine t-stat. Funny aside here is that the engine t-stat and the external t-stat use the same temperature regulating unit. So you'd think if they're both using the same regulator (same activation temperature) that they would open at the same time. But they don't.