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I have found residue coating the inside of my new coolant tank - concentrated on the exposed surfaces near the cap. The residue is brown (with maybe a tinge of green). Additionally there seem to be a flakes of sediment in the coolant.

The reason that I was checking is related to the fact that level was a bit low a month ago and I wanted to check if it had fallen after topping it up. It had, but the loss was maybe 200 ml. At the time there was no residue in the coolant tank.

Key facts

  • Car has run fine and generally quite cool (82C on highway)
  • No CELs (checked with Durametric)
  • A new expansion tank and cap were installed in April along with new OEM coolant
  • When I topped it up, I used a bit with a bit of Waterwetter and filtered water (combined 300 ml max) - no residue at the time.
  • No evidence of fluid eaks on the ground under the car
  • Oil was changed in 3000 miles ago, level appears good (may have consumed 1/2l over the past 3000 miles) and colour is looks fine. Oil filler cap is clean as a whistle - no milkshake.
  • I noticed a slight high pitched whine from the rear when I started the car today - definitely related to the accessory belt - thinking perhaps a failing WP?

BTW the engine is a factory re-manufactured engine which was installed in 2008. It has about 35k miles on it.

When I saw it, I thought intermix and my heart fell. Does this look like intermix? Could it be the Waterwetter that I used in the top up reacting with the coolant?

I know intermix is fixable, but before I go there I would appreciate any other ideas. If it is intermix, am I correct that the sources are: (1) cracked head; (2) AOS; (3) spark plug tubes or coil packs; (4) oil cooler?






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  • Moderators

Intermixes are usually not limited to a small amount located in one area of the system only; usually, when there is an intermix issue, the coolant looks a lot like hot chocolate, which does not appear to be your case (judging by what I can see of the contents of the tank).

But I do need to ask why you are using an aftermarket additive in a coolant mix that is very good on its own, but has a tendency to "not play well with others"; and why you are using "filtered water" when the spec is distilled water.......

Edited by JFP in PA
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But I do need to ask why you are using an aftermarket additive in a coolant mix that is very good on its own, but has a tendency to "not play well with others"; and why you are using "filtered water" when the spec is distilled water.......

Good points.

I have had success with WaterWetter in my 951 in the past. As for the filtered water, I only need about 100 ml and figured I could probably get away with it.

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We normally recommend against using any additives, simply because they are not necessary in these cars, and because you never know how they will react with the coolant mix.

The problem with using anything other than distilled water (about a $1 a gallon at any supermarket) is that it adds dissolved minerals to the system, which react with the coolant mix, potentially shortening its life, or causing other issues such as the type of sediment you are encountering.

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Here are some pictures of coolant that I extracted from the expansion tank with a baster and left to sit overnight. (the jar is roughly 2 1/2" in diameter)

The black specs look like they could be plastic and are small (under 1mm) and thin.

Whatever the residue is sank to the bottom of the jar and is not floating on the meniscus. It also concentrated in the middle (picture 2)and did not flow quickly when I tipped the jar (picture 3).

I am going to have the coolant system drained and flushed and may have the water pump investigated as a precaution (I am wondering if it is failing).

I am hoping that my top up may be the cause of the issue and that the WaterWetter has created the problem




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