Effect on oil pressure from completely crushed oil cooler line?

[bpu699]

Most of our cars have some degree of crush to the underbody oil cooler lines along the passenger side...most folks eventually go to fix this.

Obviously this effects cooling to some degree, though cars with very crushed lines still don't seem to over heat under regular use...

What if the line were hypothetically completely crushed...ie. Zero flow? Then what?

Would this effect oil pressure? The thermostat bypasses flow at low temps back to the engine. At high temps it is open to the radiator. But if flow can't get to the radiator, would the thermostat bypass it back into circulation?

What about oil pressure. Would it be lower if the line were completely crushed? I know this is the scavenge side, but if the line is blocked, won't this effect the oil supply to the oil pump in general?

My line is partly crushed in several places, yet the car never runs hot. Just trying to figure out if its really worth attending to. If it further increases oil pressure, then it might be worth doing...

Anyone notice an increse in oil presure once all of the dings were taken out?

[HawgRyder]

It should not have any affect on pressure (other than when the oil temp goes up the oil will thin out)....but you will get no cooling effect from the front cooler.
Bob

[Eagledriver]

On a stock system, there is a pressure relief valve that will bypass the front cooler if the lines are blocked. This will however raise the pressure in the scavenge circuit to the level that opens the pressure relief valve. Not likely to cause much harm, slight loss of power due to the increased load on the oil pump. I would say that if the lines still get hot when you drive and the oil temp stays where you want it, then don't worry about it. Uncrushing the lines turned out to be pretty easy on my car using the compressed air and propane torch method.

-Andy

[Walt Fricke]

Andy

What air pressure did you use?

Is the propane torch cool enough that you aren't going to soften the tubing so much that the (proper) air pressure will blow it out?

I need to do this for peace of mind on my SC. Looks like a jack's plate got in far enough to squish one some on both sides of the jack point receiver. I can't imagine where that could have happened, but there those dents are.

Walt

[stownsen914]

Actually I believe crushed oil lines can be quite a large problem, especially if the line gets completely blocked. The lines going to the front of the car should all be in the scavenge side of the oil system, so blockage doesn't immediately affect oil pressure in the engine. But keep in mind that oil flow through the cooler and associated lines isn't optional -- all the oil picked up by the scavenge side of the oil pump will try to flow through your crushed line, even if it's blocked. If the oil has nowhere to go due to blockage, there will be massive pressure increase between the pump and the blockage. If you're lucky, an oil line or the external oil cooler will blow and you'll notice it before any further damage is done. If you're not as lucky, the pressure will overwork the oil pump and damage it. I read once (Bruce Anderson's book?) that such a situation caused the oil pump drive shaft to snap, and the engine blew. Even if the engine doesn't blow, the only way to fix a damaged oil pump is to tear the engine down.

Keep in mind that the pressure release blowoff is on the pressure side of the oil system (at least in air cooled 911s), so won't help with a blockage in the scavenge side of the system.

I suppose the above situation must be pretty rare, but if you see significant restriction in oil lines, better off trying to fix it to be safe. My .02 ....

[Eagledriver]

I used about 90 PSI. I wanted to use more (trying for 120) but my set-up was leaking and I was only using a small 12v compressor so 90 was all I could get. I used MAP gas to get enough heat and just moved the torch around to keep from overheating any one spot. I moved the flame in about a 3/8 inch circle and along a 3/4 inch dent. I didn't get the dent all the way out, just about 3/4 of the way so I was sure it wasn't restricting the flow. I never had any indications that the tube was getting close to blowing out. The dent just slowly rose once it got hot enough. I could control the rise with the heat. As soon as the flame was removed the expansion stopped. I just used some hose from Ace Hardware with some pvc pipe ends and a shrader valve to apply the pressure.

-Andy

[Walt Fricke]

Stownsen914

Your 0.02 are misplaced. The external oil thermostat, through which all oil sent to a front oil radiator must pass, includes a pressure relief system. This was correctly pointed out in an earlier post by Andy. So crushed front oil lines will not result in extreme overpressure in the scavange line.

Now, if one is using an aftermarket oil thermostat, things may be different. But the Porsche thermostat has both functions - witness the two separate caps it has. If you disassemble one you will see how all this works.

That doesn't mean one can safely ignore the situation under all circumstances.

It is true that there are also two pressure relief systems in the high pressure side of the oiling system, one more accurately a pressure regulator, and the other an emergency or last ditch relief valve. But those serve different functions.

[stownsen914]

Originally Posted by Walt Fricke

Stownsen914

Your 0.02 are misplaced. The external oil thermostat, through which all oil sent to a front oil radiator must pass, includes a pressure relief system. This was correctly pointed out in an earlier post by Andy. So crushed front oil lines will not result in extreme overpressure in the scavange line.

OK, I didn't read the whole post first! But what happens if the crushed line happens between the engine and the thermostat? I thought that at least in some 911 models the thermostat was located up front, so there would be opportunity for a crushed line to cut off flow and not be rescued by the thermostat pressure relief. Perhaps the pressure relief system is meant to address a blocked cooler.

Scott

[chrismorse]

I just started a thread, over in Tec about using HDPE for a skid plate to hang lower than the oil lined. My questions are about size and attachment of the block, (like 1.5x2x24 inches), to the underside of the car, between the jack receiver and the front fender, where the lines make the turn up into the wheel well.

Has anyone done this???

Attachment or size details???

Thanks,
chris

[Walt Fricke]

On the relatively early (nowadays, I'd say Carrera 3.2 and before) 911s, which are the subject of this discussion, the external thermostat/valve is in the rear. From the 2.7s on they are all toward the front of the right rear fenderwell. The '72, with its forward (of the rear wheel) mounted oil tank, I think has this in the oil tank console. '73? Not up front.

The lines from the scavange outlet from the case to the thermostat are fairly well protected. The cars which had the desireable exhaust headers (no crossover) have a nice steel line which curves under the tranny bellhousing, and is what a guy wants. It won't crush absent a huge smash (unlike the brass alloy lines up to the front and back).

The exhaust crossover cars can't use this because the crossover uses the space, so they have a complicated system going around the rear of the engine. This is somewhat more exposed and has some rubber parts. But the rest is steel, so unlikely to crush. The rubber line is more apt to break/cut/leak than to cause a blockage.

Short answer - if the line before the thermostat/relief assembly gets crushed (or the line from that assembly into the oil pump), you have bigger problems to deal with than that blockage.

[chrismorse]

Any skid plate experience out there??

Tomorrow, i amgoing to see the client that was waiting for me when the car dumped 12 quarts in2 seconds. That was a thermostat popping up with stripped studs.

The roads are so bad here behind the redwood curtain, i feel the need for some kind of skid plate to prevent another expensive catastorphy.

thanks,
chris