Need help blown 3 aux oil coolers

[dsfnctn]

I have tried to understand the function of the aux thermostat on a 78 911 and need a bit of help to fully understand whats going on. I seem to be having more of my share of cleaning up oil in the last few months.
It started when my 3.0 race car with a center mounted B&B cooler got lowered and then the rear tire wore thru the oil line. When I replaced the oil line and started it up the front cooler blew. My friend told me about a radiator shop so I had it fixed.. When I reinstalled it and went to start it up the cooler blew again. I changed the whole system to a Carrera cooler and a 964 cooler. Started it up again and the 964 blew. Well I just had to keep messing with it and took out the thermostat and it seemed to opperate fine. I bypassed the 964 cooler and started it up and now blew the carrera cooler.
Clean up Isle 3 again.
SOoooo, it looks like the thermostat opens on the return side but somewhere in the system I have to much pressure. The engine oil gauge looked fine and all the last blow up happened while the car was ideling low and cold. Also it just sounds wierd by the tank hose area like smething is restricted. anyone got any ideas?
Thanks for your time

[Steve@Rennsport]

The factory thermostat also functions as a pressure relief device, protecting the from cooler from just such occasions.

I'd recommend disassembling yours (assuming its the Porsche, NOT a Mocal) to check it out very carefully as thats the root of your issues.

[patkeefe]

If you do a search here for oil systems, there are tons of posts and schematics on the system. My understanding is the two pumps (the oil pump is really two pumps) are somewhat separate. The pressure pump circulates oil from the tank to the internals. The scavenge pump sucks the oil from the case, and sends it out to the thermostat, cooler and back to the tank.

911 3.0L SC oil cooler system.

[patkeefe]

I also believe the factory aux thermostats allow a small amount of oil to always flow to the front cooler. I have had thermostats go bad; the results are ugly.

[dsfnctn]

Well I did a little digging and found the return into the tank which looks like it goes to the filter is restricted. I tried to blow through and nothing . My spare tank is free as can be.

[Walt Fricke]

Yes, the return line goes through the tank directly to the filter. Oil which gets past the filter drops right down into the tank. However, I bet your spare tank doesn't have a filter installed? I have never tried to blow through a filter, so don't know how restrictive that is to lung pressure.

Changed your filter lately? The Porsche recommended filters have a bypass feature, so, if they get clogged, oil (unfiltered) still can get through, so there is something returning to the tank, and you aren't getting a huge overpressure. A filter without the bypass feature could clog and greatly increase resistance.

Hard to imagine anything large enough to block any of this happening without you knowing it, though. Hard to miss an engine blowup.

Swapping tanks isn't all that hard a job.

[HawgRyder]

Walt...I ran into a clogged filter one time...it had some water (condensation..?) in the oil...and combined with the type of filtering material inside the unit...it turned into something like concrete!
Yes...it was a Fram...sry guys...small block chevy...but it proved to me that wierd things can and DO happen.
My other thought...is the pressure release valve working?
If that sticks in the case...and the oil is cold...you could get very high pressures.
Bob

[Walt Fricke]

Well, he says his measured pressures are OK. And even if both of the pressure valves in the case failed, that would not lead to overpressures on the scavenge side, would it?

Maybe his filter has a problem like you had. That would also mean that the pressure relief valve in the factory external thermostat would do no good either - the high pressure would get to the front cooler no matter what, because the relieved oil would have no where to go.

[patkeefe]

I did some tests on my stand this winter. The Fram on the stand has an internal bypass. I also have a manual bypass. Pressure in the case does not indicate pressure in the scavenge system. There are a few of these oil vids; here's one:
Cold Oil - YouTube

[AlfonsoR]

Is ig possible that a piece of rubber from the tire or the hose got into the line and is now restricting flow?

[dsfnctn]

Originally Posted by AlfonsoR

Is ig possible that a piece of rubber from the tire or the hose got into the line and is now restricting flow?

BINGO I love this forum . The whole problem started when I changed out the hose. I am going out to remove the tank and Im thinking that I must have comething like maybe a packing peanut or maybe one of those plastic inserts that keep the hose protected or maybe part of a rag?
Ill be back. Thanks everyone

[HawgRyder]

Walt...I just realised from your post...
If the front cooler is blowing...and the tire had something to do with it...then yes...maybe a piece of junk got into the line in the return line from the front cooler to the tank.
This would effectively block the flow AFTER the cooler...and prevent the oil from reaching the tank.
The pressure would build up...but because the relief valves in the case are for the pressure side of the sysytem...the scavenge side of the pump would be dead ended.
It's just a matter of the weakest link...in this case it appears to be the thin area of the front cooler.
Bob

[dsfnctn]

Great news. I removed the tank and the return to the filter was plugged solid.I drilled a hole in the filter and plugged the center outlet from the filter and blew thru the filter . First nothing and then bam and it shot out something so fast we couldnt see what it was but the plastic part in the pic showed up on the floor. Its a plastic plug from some new part . Im not sure but I have seen it somewhere before. The pipe has no restrictions. Is this a great place or what. Thanks again for all the help.

[KTL]

Wow................

That looks like a typical red AN plug made by caplugs for a female hose end

Caplugs - Hydraulics

[Walt Fricke]

I don't see threads on it, though there may be. Are there AN plastic plugs without threads? All mine have them.

It looks a bit like some other push-in plug which comes with some part I've purchased more than once, but can't quite visualize it. New brake master cylinder?