Oil in coolant? Do you need to drain oil to change oil cooler?

[AustinPorscheBill]

---

Background.

Bought 1998 986 two years ago.  Had to replace a radiator shortly after taking possession, when I drained (yellow OEM?) coolant, it was clear, i.e., not murky.

Two years later, I had the water pump fail.

Replaced pump (Pierburg) and thermostat (low temp, first a Wahler that was defective -- on stovetop, wouldn't open 'til 180 -- then Motorad).

Problem.

When I drained the coolant this time (Porsche pink G-40), it was murky, not clear.

Looks like I have something, maybe oil, in the coolant.

It was weird in that whatever the contaminant is, it didn't separate from the coolant/water after I left it sit for a while, and it looked greyish, not brownish.

 

(FYI, my oil, per the dipstick, is still clear-fresh:  it was changed about 2,000 miles ago and looks like I poured it in yesterday.)

And whatever the contaminant was, it got lighter -- but never fully went away -- with each subsequent flush (three in all, two with Prestone cleaner).

No water in the oil that I can tell at the dipstick (again, oil looks clear and fresh).

I pressurized the coolant system to 10psi each time I flushed and refilled, and it held the full 10psi for 30 minutes.

I also did a vacuum method fill and the coolant system held a high vacuum, also for 30 minutes before I sucked in coolant.

Not sure whether a leaking oil cooler would reflect in either a pressure or vacuum test.

Prior to the water pump failing, I had no measurable loss of either coolant or engine oil.

Any thoughts?

Also, some questions about an oil cooler replacement, if I end up going that route.

Where is the most likely oil-coolant barrier failure:  in the oil cooler itself or at the o-rings at the engine-cooler interface?

Should I first try just replacing the o-rings or should I expect to replace the cooler and o-rings?

Do I need to drain the engine oil (if it is not contaminated of course) before removing the oil cooler?  As the oil cooler is on top of the engine, it would seem that all the oil would have drained to the sump when not running -- or is there a reservoir and/or check valve that maintains oil in the cooler body?

In advance, thanks for any help.

 

[JFP in PA]

Usually, the internal walls fail in these oil coolers; when an O-ring goes bad, you typically get an external leak of the fluid passing thru that seal due to the internal pressures.

 

Before removing the cooler, you need to drain the cooling system, but not necessarily the oil although many change the oil after servicing the cooler, just to be safe.  Four small fasteners hold the cooler in place, and it is a very good idea to lift the cooler slightly before removing it and sliding a plastic bag under it to catch any residual fluids and prevent them from going down the wrong port.

 

That said, if you have pressure tested the cooling system with no pressure loss, it would be my opinion that nothing is leaking, you just have cloudy coolant.  Coolant can get cloudy for several reasons, the system was filled with a mix of coolant and tap water, the coolant is old and crapping out, debris in the system from prior repairs, even someone adding the wrong fluid to the coolant tank.  You can drain the system, flush it with clear water, and then refill with a 50/50 mix of fresh coolant and distilled water (use distilled because the minerals in tap water reduce the service life of the mix).