Can this leak, that much?

[djdsc]

The ’77 911S was parked outside during the N. Calif. cold snap of a few weeks ago, yea I know it is all relative. None the less, it was in the low 20’s the morning this oil leak happened. The car had sat over the weekend and puddle oil on startup.

From the pictures you can see that the leak was coming over the front of the case and what looks to be between the head/cam tower and oil cooler. It is also running down the side of the case. Trying to diagnose from the drip pattern it doesn’t seem like this could be oil cooler seals, more like the oil cooler thermostat seal. The pictures of the top of the case and the thermostat were taken 3 weeks after the leak occurred so it is hard to tell how wet it might have been. The Top of the oil pressure switch was dry. The oil cooler thermo O-ring, pressure switch and breather gasket were all replaced about one year ago (7,000 miles).

Will the oil cooler thermo O-ring leak that much if gone bad? The green O-ring doesn’t seem to be as large in diameter and the red one pictured in 101 Projects. Should I look elsewhere like the rocker ends?

[304065]

I think you would see a puddle of fresh oil on the top of the engine next to the thermostat. I think you blew a hole in the oil cooler. Classic symptoms, cold weather, cold oil, startup pressure, thermostat stuck open (it's California, right? so it's usually open). I would take some more photos, clean everything, start the engine and start looking for leaks. Some dye added to the oil will leave a trace that can be examined with a UV lamp, search here for details.

Good luck! At least you didn't lose all the oil!

[djdsc]

Yep, split in the weld of the oil cooler.

Is this the usual area of failure when one of these goes? Why wouldn’t the seals go first, they seem like the weak link not the welds?

Is this an indication of an oil pressure problem, relief valve; that should be checked out?


The split is clearly visible running down the center of the weld.

[304065]

There are three moving parts at work:

1) The oil pressure relief valve. In a post-76 car or one modified with the "oil bypass modification" excess oil pressure from the pressure pump is routed back into the feed for the pressure side of the pump instead of being dumped into the sump. This allowed Porsche to reduce the size of the scavenge pump while still achieving proper scavenging. Oil pressure flows from the pressure pump to the. . .

2) Thermostat. If hot, oil is routed through the oil cooler before flowing to the galley that feeds the main bearings. If cold, oil is routed directly to the bearings, bypassing the cooler which would surely burst if fed high pressure, cold oil, as you have seen.

If the pressure is too great in the oil galley feeding the main bearings then the system reverts to . . .

3) The oil overpressure safety valve. This is set at a higher threshold and WILL dump excess oil into the engine case if its threshold is exceeded.



In your case, all three systems failed. Why? Possibly the pistons were stuck in the bores, and the thermostat was stuck. The plugs in the bores can be pulled to clean them and see if the pistons are free to move, and the thermostat can be boiled, search the archives for a thread where Warren did exactly that, to verify correct operation.

Since the cooler has burst I don't know if it can be saved but you might call Pacific Oil Cooler, they are the experts.

Sorry to hear your news but at least you KNOW the problem!

[djdsc]

John,

Thanks for the description and the diagram. I will check out the other components.