Coolant system service

[BReyes]

Prepared with a couple gallons of antifreeze so I could flush the system (third time in three years), I first inspected the system. I previously noticed a hairline crack in one of the return coolant hoses and am replacing the hose before it begins to leak. Took couple trips to the dealership, they are still trying to get me the correct hose.

So I changed the fuel filter and after removing the access panels had a good opportunity to inspect all the hidden hoses and lines. Looks like new under there. No leaks.

Found one area with crud on it and will be looking into resolution.

Attached pic shows (macro) of rear of vehicle forward of engine. The "crud" was dried corrosion looking stuff (and slightly pink [so coolant] with the consistency of dried dirt, surrounding what appears to be a small (looks like dark pink plastic in the pic 1/4 inch wide) plastic lever that works a diaphram inside the little plastic piece pictured. The hoses pictured (elbows) are approximately 1 inch in diameter and one of them is a unque hose 1 inch 90 degrees and fused (vulcanized or molded into) a larger 2 inch or 1 3/4 inch hose (larger hose that this little hose pictured goes into is not pictured).

Question: Do you know what is this, and what it does? What happens (what does the car do)when this part becomes faulty?

Thank you.

Regards,

Edited October 30, 2009 by BReyes

[amcleod1]

Since you have a 1999 996 tip, that part looks like the coolant shut off valve (P/N 928 574 573 03) in the ATF coolant sub-circuit. Basically as I understand it, the shut off valve moderates the temperature of the ATF in your tip transmission. If faulty, and depending on whether faulty open or faulty closed, would run your ATF temperature too high or to low. It takes a coolant feed from the main coolant circuit (via the hose that you mentioned is fused with the larger 2" one) through the shut-off valve, then through the ATF heat exchanger and then eventually returns back into the main circuit via a series of interconnected return hoses just ahead of the water pump (but after the thermostat).

FYI....This is the same shut-off valve as fitted to a 928 (I used to own one) to control the temperature in the cabin. Any current/prior 928 owner's would know this part to be the troublesome recurring cause of what was described as a "hot air" coming from the centre vent of the HVAC system when full cold selected. From this experience I know that even if the valve appears to be working externally (i.e the vacuum actuator moves the lever across full range - full-open to full-closed) internally the valve seal that opens/closes the water circuit can be faulty. If you replace it make sure you install in the correct direction for coolant flow - another common error on 928s when replacing.

[RFM]

If the valve fails due a vacuum leak it remains open, the gearbox is fully cooled and the engine temp. drops from approx. 85°C till approx. 70°C while driving.