Cooling question

[johnmh]

For background, my car is a U.S. spec, manual gearbox, 996 3.4 convertible. I recently purchased it cheap knowing it needed major service work. 

 

So far I have pulled the engine and installed a new AOS, oil cooler, water pump, thermostat (not OEM - supposed to open at lower temps), coolant reservoir, cap and hoses.  I have also done other engine work such as variocam guides, spark plugs, clutch, pressure plate, TOB, IMS, RMS and resealed the entire engine.  I intend to add a third radiator at the front of the car as well.   I have had good results with Evans NPG coolant in other cars I have so I intend to use it in the 996.  To use it I needed to drain the car as much as possible, run it briefly with prep fluid before draining it and adding the NPG.

 

The issue is getting the car to run a normal temp.

 

I first added about 1/2 of the recommended 22.5 liters of fluid (until the reservoir neck) and started the car.  It ran well, but got quite hot quickly.  The rad cores and pipes remained cold even after the thermostat should have opened. 

 

I then placed a sealed tube with a Schrader valve on the open reservoir filler neck and added a few psi of pressure with a bicycle pump.  The bleed valve was open.  A few pumps and gurgles later more coolant would go in.  After a few of these pressurization cycles, it burped a lot of air out, so much so that I could fill about 22 liters of fluid in.  Still, I started the car, revved it a few times and the rads barely got warm while the temp gauge approached max ( I shut the engine off as it exceeded 180f). 

 

Following more examination I noticed that the left (driver) side rad has a hole in the centre where lots of crusty pink coolant has escaped and dried over time (a replacement is on order). 

 

I removed the right side rad (it seems fine, no blockage or leaks). 

 

Two questions - 

 

What is the normal operating temp for a 996 engine when warm?

 

There are 2 rubber hoses which connect to the top of the coolant reservoir.  The bigger one towards the rear of the bleed valve (1st photo) seems to connect to the small tubes which vent from the tops of the radiators. Where does the small diameter one in the second photo connect to?

  

[JFP in PA]

It sounds like you have an air pocket in the system.  The correct way to refill these systems is under vacuum, removing the air before sucking in the premixed coolant.

 

Usually, the smallest line on the coolant tank runs to the top of the oil cooler to help get air out (the oil cooler is the highest point of the cooling system).

[johnmh]

Thanks. Best way to remove the air pocket? The system is completely empty now while I wait for some parts. Does it help if I lower the front of the car while raising the rear?

[JFP in PA]

The best way is by using a tool such as the Uview Airlift, which is also the factory tool for doing this.  Some people resort to all sorts of tricks like tilting the car at weird angles and such to get the air out; but the corrrect tool make refilling the cooling system a 5 min. Job with the car sitting on the ground.

 

 

[creekman]

I had the surge tank hose come loose from the left radiator, so I made the repair and tried to use the Airlift tool, but because there was a residual about of coolant left in the system it wouldn't work.  I filled the system up the best I could, drove the car and it over heated, then refilled and got it over filled and it over heated again.  The system is very prone to trapped air and unless you completely drain the system and use the Airlift tool to fill it I think it's problematic that you're going to have trapped air for some time.

 

The rub is getting the system drained, I hate messing with good hose connections and I don't know which hoses would get the job done.  Maybe removing the hoses from the aluminum water pipes under the car.  Also, the Porsche factory 3rd radiator is for an oil cooler, I had one made which is larger than the stock 3rd oil radiator.  I'm not sure what the difference is between the oil and water radiators.

[Loren]

If you want to know about a third radiator install I covered it here: 

This was back before the days of Uview Airlift so I had to drive the car for a few minutes then top up radiator - this took a couple of days. So, Uview Airlift is definitely the best choice.

[JFP in PA]

1 hour ago, creekman said:

I had the surge tank hose come loose from the left radiator, so I made the repair and tried to use the Airlift tool, but because there was a residual about of coolant left in the system it wouldn't work.  I filled the system up the best I could, drove the car and it over heated, then refilled and got it over filled and it over heated again.  The system is very prone to trapped air and unless you completely drain the system and use the Airlift tool to fill it I think it's problematic that you're going to have trapped air for some time.

 

The rub is getting the system drained, I hate messing with good hose connections and I don't know which hoses would get the job done.  Maybe removing the hoses from the aluminum water pipes under the car.  Also, the Porsche factory 3rd radiator is for an oil cooler, I had one made which is larger than the stock 3rd oil radiator.  I'm not sure what the difference is between the oil and water radiators.

 

I don't understand why you had a problem with a partially filled system using the Airlift tool, we do exactly that just about every day.  As long as the tool adapter at the surge tank is above the liquid level, and the engine is not hot, the tool will not draw in coolant.  When you start with air trapped in a partially filled system, throttle the compressed air feed slightly to allow the system to "burp" the air out gradually without causing a surge of liquid towards the tool.  When the system stops "burping", you can open the air feed wide open and pull the system down to full vacuum before pulling in the additional coolant mix needed.  With a drained system, refills take about 5 min.; starting with a partially full system it may take you 10-15 min but when you are done, you won't have any further issues.

[creekman]

I've never had any luck doing a partial Airlift, and the Airlift directions specifically state that the system has to be completely drained for it to work.  But if it worked for you that's great, I wish I knew what you know.  

 

I think Loren's advice is the best on a partial fill...  Just drive the car for a few minutes, then let it sit, eventually, it will clear itself of air.  I tried one of those large yellow funnels that fit into the surge tank and allow for the water to back up in the funnel.  I did that one day, but all of a sudden coolant back up like an erupting volcano, coolant everywhere, but it turned out that the system had belched all the trapped air and from that point after filling it was happy.

[johnmh]

The good thing is that the system is bone dry, all new radiators and hoses will ensure that.  I have a EBC power brake bleeder system which plugs into my compressor which I have had success with (for bleeding brakes) in the past; I was considering hooking it up to the reservoir and using it as a source of vacuum to draw coolant through the system.  

 

That Airlift tool does not seem that pricey, maybe the $100 may be worth it (and I have other cars with oddly shaped cooling systems I can use it on).

 

Forget the garage space, this 996 is making me think about expanding my available tool box space with all the new and strange tools I require to work on it.