Scavenge side operating pressure

[chrismorse]

Hi guys,
I’m seeing oil residue on my Carrera fender cooler(in 74 coupe) and am planning on cleaning it up and running a leak check on the bench. No obvious oil trail.

I don’t want to over-pressurize (and possibly cause another/worse leak).

Once I adapt some fittings to pressurize it I will pump it up and hit it with soapy water.

What is a safe/effective pressure to use for the test??

The engine is out for a lot of work, so I cannot test the scavenge side pressure - my guess is that it is a lot less than the operating pressure.

Thanks,
chris

[Flat6pac]

The scavenge side is flow, not necessarily pressure
Bruce

[chrismorse]

H Bruce,

I think you're right, the flow has got to be about the same. I just don't have any idea what pressure is safe to use to test the cooler, I'm guessing the cooler and filter/lines are more free flowing and don't want to use too much pressure to check the cooler.

Thanks,
chris

[fanaudical]

Best guess: around 25psig should be sufficient for a leak check if you want to be sure not to over-pressurize but still make soapy bubbles.

Anybody have a recent test report from Pacific Oil Coolers? That might indicate their test pressure.

[manbridge 74]

From the service manuals....

Oil filter contains a bypass valve to guarantee a sufficient oil supply if the oil filter is dirty. Bypass valve opens as soon as pressure exceeds 29psi (2 bar).

[dannobee]

The oil pump is a positive displacement pump. On the pressure side there are a couple of valves to bleed off the pressure, but there isn't anything but the oil filter bypass to limit the pressure on the scavenge side.

911 3.0L SC oil cooler system.

Scroll down to Mike's experience in post #8, pegged the gauge at 250psi.

[stownsen914]

There isn't anything to limit pressure on the scavenge side of the oil system. I'd heard that it can go quite high, but hadn't seen anything published before (thanks for that dannobee).

Note that the bypass on the filter is there to ensure continued oil flow if there is a blockage in the filter, and possibly to prevent blowing out the filter from over-pressure. It isn't designed to limit overall system pressure on the scavenge side like the pressure relief and safety valves in the crankcase do for the pressure side of the system.

[T77911S]

pressure is a result of resistance.

take a garden hose.
with nothing on the end there is no pressure with the water coming out.
put your thumb over the end and now you have pressure.

hopefully the residue is from the connection

[chrismorse]

Originally Posted by fanaudical

Best guess: around 25psig should be sufficient for a leak check if you want to be sure not to over-pressurize but still make soapy bubbles.

Anybody have a recent test report from Pacific Oil Coolers? That might indicate their test pressure.

Thanks Fan,
I took your suggestion and called Wayne at POC. His recommendation is to use 80-100 psi for the test.
Test and clean: $ 195.00 + repairs
Turn around is 10-14 days.

Just for fun, i asked about the sump tank: $245, + repairs, if needed. They either have or can make any needed gaskets

Cap all openings and double bag the item.

My plan is to get some adapting fittings and test the cooler. I've got a couple of coolers from the green car, so if the carrera cooler bubbles it goes in the box.

Will report back on outcome.
chris

[Walt Fricke]

If there is a leak, you need hardly any pressure at all. With soapy water over wherever you think something might leak (including full immersion), you could just blow through a tube to create enough pressure to find a leak. It isn't like leaks in items like this only manifest themselves at elevated pressures. Air is really slippery stuff.

On the other hand, if you want to see if something - which doesn't leak - is strong enough to withstand a particular pressure, then you need to use that pressure (or some higher pressure, for a safety margin).

30 or so years ago a guy who had installed a pressure gauge on his scavenge line close to the engine said he was seeing pretty high pressures. However, after the friction/restrictions of a front cooler (I think he didn't have the stock external thermostat) and all the lines, the pressure at the oil filter was much lower. I no longer have access to e-mails from then.

While the external oil thermostat has a built in pressure bypass, the engine oil filter system has no such bypass, just the cold oil bypass. Which means that a warm engine is going to put maybe 5 Bar or 75 PSI though that cooler.

If it is easy enough to do, 100 psi seems reasonable for pressure testing. Of course, that requires a lot more specialized fittings than just low pressure leak detection. And perhaps some safety precautions as well? 100psi isn't like a nitrogen bottle, but still could be dangerous if something burst.

[r lane]

When cold, enough to pop a front cooler if you aren't running t'stat.