Terrible gas mileage - white slime in valve cover vent hose
 

I get terrible gas mileage on my 1996 A4 2.8 (10 mpg1). Wanted to change the Engine Coolant Sensor today (Autozone does NOT have the black square 4 blade sensor, only green, oval, 4 pin).

Removed the valve cover vent hose (black, corrugated plastic, coming out of the rear of each valve cover).

Full of white slimy slime (and water?).

What is that indicative of?
Running filthy rich?
Plugged cats?
Bad PCV valve?

Attachment 87659
Attachment 87660

Engine not running high enough temp, bad thermostat. Engine not getting a chance to hit a high enough. Like you only drive a mile a day. Engine needs high temps to boil the water from the system. Breather system has blockage and nothing can escape is another possibilty.

Thermostat: check (ordered). True that it can make the engine run way to rich?

Breather system: on driver side, the hose T ing off the valve cover hose was clean (going to the plastic Y then to the front of the engine). What else to check (for clogging and functionality)?

What symptoms to expect from a clogged cat (only one, the other is rattling around loose so it can't be blocked)?

Vacuum is at 18 (idle). Engine runs smooth.

Just did an oil change. With new thermostat installed, should I seafoam the intake (through vacuum hose)? IIRC, after seafoam, oil should be changed, or?

Engine coolant sensor 058919501A
 

Picked up at Autozone, but no fit (was oval and green, 4 round pins). The 058919501A is black, square and has 4 blades.

Sources for the part?
Other part number?
How to ensure it is the right one (seems like there are several versions used for 2.8 V6 12V; some maybe super-seeded?)

ECS shows several, looking at this one (still about a week til it gets here):

Water Temp Sensor
Brand: ES#: 2524963 Mfg#: 058919501A~MTC

Ships in 4-7 days
$13.49

Bad oil cooler possibly
 

I dealt with the same issue for 8 months. The least expensive way of fixing the hose issue is reusing the ends and making your own breather hose, I think it was 1/2" diameter hose you can get by the foot at any parts store. Use clamps to attache the hose to the ends for a secure fit. After changing the hoses, thermostat, sensors etc, I started to monitor my engine oil. I was loosing about 1qt of oil between 5000 mile oil changes. Also in the summer my oil temp would be contantly around 250F when going 70-75. After changing the oil cooler I no longer loose any oil, my oil temps stay low, haven't had any white resifue in my breather hoses. I read that the oil cooler sometimes cracks causing a mix between the oil and the cooler. If you can change your own oil, you can change the oil cooler with no problem. Hope this helps.

I dont know what it is but was getting the clogged egr valve code so I took mine apart and found the same , so cleaned it out and tried to get egr valve off ...... wouldnt come off so if you know why I could also use some answers . Have the same car Thanks Renee

re that hose...
 

that PCV hose looks like it has NEVER been removed and cleaned.

Your problem is most likely bad valve cover gaskets letting moisture in to the valve covers and causing this sludge when it mixes with oil.

You can remove those ends and re use them, look at them carefully you will see how. then use some standard pipe to make new ones.

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unfortunately, if the hose is THAT far gone, you not only need to do the valve cover gaskets...you need to clean out the mesh filter in the valve covers themselves

Luxary Tank: built up was no solid, just slime. Hose had been off (clean) when I fixed the car (had a bad transmission and other issues). Valve covers where off, everything. What you see in the hose is the built up since I noticed terrible (1/2 of normal) gas mileage. May 3 tanks.

By now I have changed the engine coolant thermostat (was able to order the right one from Napa). Just to be sure, also installed a new fuel pressure regulator. Daughter reports she got to 200 miles on a tank for the first time (changes made somewhere during that tank). Fill up today and monitor. Can't comment on richness (as judged by CONSTANTLY white smoke, not just during warmup), since it is too warm to visible see 'rich' exhaust.

If I get an opportunity, I will also pull the plugs as soon as possible; they should also tell if 'filthy rich' running. May clean them and pull again after another tank or two.

Oil change: oil was dark, but NOT the 'milky' brown I have seen when burning coolant.

I have never heard that a bad valve covers draw water in (that could create the slime)? Also, shouldn't I have really bad vacuum then (I mean, this would be gigantic vac leak !!!).

There is now detectable vac leak (starter fluid test everywhere), vacuum is decent at -18.

no check engine light? Make sure the vacuum line to the fuel pressure regulator is in good shape and hasnt collapsed. Leaky injectors, lazy oxygen sensors, maf sensor, vacuum leaks, dragging brakes, timing belt is off (which will happen if the belt job isnt done with proper tools) My 100Q manages about 300 to a tank and im not real easy on it.

We had the O2 sensor CEL for a while (downstream); one replaced and both swapped position (I had mixed up the sides).

I will run full scan today again. Currently no CEL.

Timing belt: I think I paid a lot of attention getting the timing right, even posting and complaining to Blaupart that there is too much 'slop' in their rental cam tool.

Vac leaks: I replaced all hoses from the 'spaghetti pile'.
Sprayed LOTS of starter fluid and can't get her to 'hickup'.
Vacuum is -18 at idle.

MAF: dirty or faulty? Should I data log MAF readings in Volt and g/sec with vagcom while driving?

FPR changed to known good one, vac line clean and new.

Dragging brakes would be hot: ruled out

Anxiously waiting for next fillup to see if anything changed.

Note: Driver side cat rattles around in housing since 2 weeks. Other side no sound. Can clogged cat cause it?