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Old 03-18-2018, 05:25 PM   #1
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UGH - oil in the water - guess I need a oil cooler

In trying to track down the course of the oil stain on the ground inside the rear passenger wheel area every time I park the car, I looked at the oil fill/dipstick/radiator fill cluster in the rear trunk. I looked there because in searching in vain for the source of the oil leak, it appeared to me that the rubber hose that extends toward the ground in the area of the rear passenger tire had oil residue inside it, and a remain of a drip from it. I assumed this was the drain hose for the rear top well drain on the passenger side. In looking at the cluster in the trunk, the plastic trim plate that forms sort of a "floor" to the well they sit in was shiny with what appeared to be oil residue. The area around the dipstick was absolutely dry. Most of the residue seemed to be around the radiator fill cap. I cracked the cap open, and oil ooozed out - plenty of oil! This was followed by a seemingly unlimited amount of golden tan gooey water. Not good. Damn, this sucks.

Does this dipstick/fill cap well area in the trunk drain out through this rubber hose as well? If so I have found the source of my oil leak. In searching, it seems that while there could be numerous sources of this oil in the water, the most common one is the water to oil cooler. I'll search for a good write up on the procedure, but this seems to be the easiest and most cost effective place to start.

It seems in my initial reading on the subject that the oil cooler itself is not terribly difficult to change, but cleaning the goo out of the cooling system is mind-numbingly monotonous. What's the best way to do this? What's the best method to drain the entire cooling system - where do I best open it to drain most of the junk that's in there? My thought is to completely drain it, and then change the oil cooler. Then I'll fill the cooling system with fresh water and the Prestone flush chemical (anyone know what it's called?). I'll run that to bring it up to temp, and then drain it. I'll use the chemical and fresh water again, bring it up to temp again and drain it. I'll fill with fresh water and chemical, and run it a day or so driving, Drain it again. I'll keep doing that with fresh water and chemical until such time it runs clean finally. I'll use chemical and fresh water each time.

If any of you have actually done this job and can offer any tips, or if any of you have any advice at all on changing the cooler, sourcing the cooler, flushing the system or anything else, please chime in here. It's terrifying to know that it could be something worse. I am strongly hoping that this is it.

For what it's worth, the engine oil is up to level and looks perfect. Once I am done I'll change it anyway. The car has run perfectly at 180 degrees. No overheating. All this started with looking for the source of the leak on the ground. See the other thread I started on this.

Hard to locate this oil leak

When I cracked the radiator cap open, pure oil initially oozed out. If the dipstick/fill cap well is connected to that drain hose, this has to be the source of my leak, at least I'm hoping it is. The car is a 2002 Boxster S.

Any help or input on this is greatly appreciated.

Last edited by Doug427; 03-18-2018 at 05:28 PM.
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Old 03-18-2018, 08:16 PM   #2
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What I think you are seeing is overflow from the coolant overflow tank (which now contains oil) popping your coolant cap and since the oil is on top, that's the first thing that gets expelled and flows down the drain in front of your rear right tire.

Fingers crossed that it's the oil cooler. I haven't changed mine (it was replaced with a new one when my engine was rebuilt) but it looks like a simple job to replace it.
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Old 03-18-2018, 11:23 PM   #3
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Have you pulled the carpet back to get a good look at the coolant expansion tank? It's semi-opaque plastic (somewhat translucent)... you might be able to get a better idea of what's going on or how much oil is in the tank. I'm with you that it could be the oil cooler, but it's "possible" that oil entered from the top (some moron could have started topping off the oil via the coolant fill...hey, it's only an inch apart). I mentioned this because (again, "possible") that cleaning/replacing the tank and a good coolant flush solves your issue without changing the oil cooler. There are several threads here on coolant tank replacement, here's just one I found with some good pics:
DIY Coolant Tank Replacement in Under 2 Hours

Best of luck
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Old 03-19-2018, 04:10 AM   #4
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Oil/coolant intermix can be caused by a number of things. If you suspect the oil cooler, it’s most likely the 4 o-rings that seal it to the block. Not hard to replace the rings and you can test the integrity of the cooler when you have it out. To verify that the oil is indeed coming from the tube, you might clean it and then wrap a paper towel on the end. And, as Birddog mentioned, peer into the coolant tank.
The other obvious possibility in that area is the bottom line of the AOS is not well sealed.
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Old 03-19-2018, 05:20 AM   #5
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I'm thinking the easiest thing to do is to just replace the oil cooler and of course the associated o-rings and go from there. I just bought the car so the thought that some knucklehead prior owner added oil to the coolant tank by accident occurred to me. I sort of doubt that however because in the little use I have given the car so far, it marks it's parking spot with a fairly good sized oil spot almost each time. If my theory that it's coming from the coolant tank is correct, that means that a fresh supply of oil is getting dumped into the tank each time I use the car. I'm thinking and hoping that BirdDog and I are correct.

I found a new Behr oil cooler on line for only $112.00, so it's fairly cost efficient to just do the swap and multiple flushes, and see how it goes from there. The refreshing of this car was/is coming along really, really well, so this new development is sort of a bummer. I'm hoping that it turns out to just a bump in the road.

Last edited by Doug427; 03-19-2018 at 05:22 AM.
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Old 03-19-2018, 03:43 PM   #6
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I just re-read your first posting on this forum...you mentioned smoke. Did you track this down to the AOS?
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Old 03-19-2018, 05:00 PM   #7
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Quote:
Originally Posted by MWS View Post
I just re-read your first posting on this forum...you mentioned smoke. Did you track this down to the AOS?
When I first drove the car it had been sitting for a long time, I believe about a year or so. The first time I really got on it hard, it smoked pretty badly, and idling after that incident it was smoking, although not to badly. After that, its never done it again. I've gotten on it pretty hard on quite a few instances, and not seen one drop of smoke since. I have a AOS on hand and ready to install, but I have quite a few other things to do to the car and that has slipped a bit in the list of priorities, as its not currently presenting a problem. It will eventually get changed, however.
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Old 03-19-2018, 08:35 PM   #8
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Before you start replacing parts, the first thing to do is to have the coolant system pressure tested. That will tell you where/what to repair.
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