Oil change after an AOS replacement

[Gadwood74]

Is it necessary or recommended to change engine oil after an AOS failiure/replacement? I've changed my AOS a couple of weeks ago and drove the car for +/- 300 miles. FYI-engine oil had been changed just before the failiure. However, I've changed the engine oil again tonight just in case, not sure if it was necessary. I just went for a ride and had the feeling the car was running better. Is it possible that the AOS failiure could have result into a coolant mix with engine oil?? This is what I was scared about. Maybe scared w/o a good reason!!

[JFP in PA]

Is it necessary or recommended to change engine oil after an AOS failiure/replacement? I've changed my AOS a couple of weeks ago and drove the car for +/- 300 miles. FYI-engine oil had been changed just before the failiure. However, I've changed the engine oil again tonight just in case, not sure if it was necessary. I just went for a ride and had the feeling the car was running better. Is it possible that the AOS failiure could have result into a coolant mix with engine oil?? This is what I was scared about. Maybe scared w/o a good reason!!

Changing the oil is not necessary unless intermix has occurred. That would be obvious, as the oil (or coolant) would have a “hot chocolate like appearance due to the formation of an oil/water emulsion. If the oil (and coolant) is clear and clean, you are fine.

[logray]

If your car suffered from intermix, and you thought it was the AOS, chances are it is going to be a result of a failed oil cooler or crack in one of the heads and not the AOS.

[Gadwood74]

Well, used oil didn't looked like a creamy hot chocolate, thanks god (or please god). I Will still have the oil tested next week.

But I think my question was not clear enough: could a defective AOS cause an intermix?

Thanks Logray for your answer, didn't thought about oil cooler.

I've been driving recent and low mileage cars since the past 10 years, so it's been a while since I had mechanical problems.

[JFP in PA]

On a 996, yes, a bad AOS can cause intermix because the AOS has a water passage in it. It is not a common type of AOS failure, more often you start sucking oil into the intake and billowing smoke. But it can happen.

[logray]

Expanding upon JFP's post, a few things regarding the AOS and intermix

oil in coolant theoretically possible = NO

coolant in oil theoretically possible = YES

1.) From the immovable RFM...

http://www.renntech.org/forums/topic/38721-smoking-2001-996-convertibe-aos/#entry210285

2.) Since watching this and other forums since 2005 I have never actually read of an intermix caused by AOS, only by oil cooler or head crack (the latter being most commonly reported).. Not saying it hasn't happened, considering as JFP points out water does flow through the AOS, but perhaps raising the possibility yours is not the exception to the norm.

To help diagnose this issue further, perhaps you could post some pics of your oil and coolant in order to steer this thread in the next direction.

Cheers all! :)

Edited March 17, 2013 by logray

[JFP in PA]

To follow up on Logray's comments, he is correct that because the AOS does not carry pressurized oil, an AOS failure intermix is a one way deal, coolant into the oil. Personally, I have not seen this, but a local dealer had an intermix car in, and after dropping the engine and pulling both heads and the oil cooler looking for cracks, discovered a very small crack in the AOS body that was leaking coolant backwards into the oil sump. Needless to say, the service manager was just thrilled over the number of hours wasted trying to track down the leak.

So, while not at all very common, it can happen and is worth making note of for future reference purposes when encountering an intermix for which you cannot track down the source.

[Gadwood74]

Thanks all for the comments, very interresting.

I just had great news - no coolant in oil. 20,000 pounds less on my shoulders (and 20,000$ securized)...

I just need to figure out where the coolant leek. I guess the next step would be a pressure test on the system as I never see coolant on the ground when parked. There's a couple of posts on coolant system testing.

[JFP in PA]

Consider adding a UV dye to your coolant, then run the car around for a bit. Take a look around the engine bay with a blacklight source and it will become very obvious where the leak(s) is/are.......