jchapura

2005 C2S ~52k miles

For the record, for multiple months prior to these maintenance procedures, I noted an oil temperature of about 205 deg F, whether the ambient temperature was warm or cold. I could get the temp to go up by keeping the RPMs above 3000 for an extended time. Most of the time the needle just stayed pretty steady at 205.

The one day, saw leaking coolant from underneath the water pump. Decided to change the water pump and thermostat myself. I also changed some of the hoses that touch other about-to-be-changed-out parts. I changed the reservoir cap. The new thermostat was labelled as "71" and marked Motorad. I have no history of whether any prior coolant system work had been done by others.

When initially draining the coolant, I used the AirLift three additional times to pull fluid to the back end of the car to get a more empty system. Then I did the parts change out. Put everything back together. The system held its vacuum for at least five minutes. I then refilled with straight distilled water, intending to "flush" out the old, yellow-ish coolant since my new coolant was Audi G12 anti-gel "red". I took it for a 15 minute spin to mix up, and heat up, everything. I drained the diluted coolant three time with AirLifts in between.

It held vacuum again. Proceeded to add 3.3 gallons of straight G12 since that's what I calculated I needed (for appropriately 50/50 against a total capacity of 8.6 gallons). Finished/topped off with distilled water.

To try to get any potentially trapped air pockets out, I turned the heater on HI and fan on high. I'm now getting about 212-215 oil temperature and the needle seems to move (up and down) more often compared to the pre-change state.

I was really hoping for a reduction in oil temperature after the change-out because of the low temperature thermostat. What might explain why the "reduction" seems to have gone the other way?

Thanks for any insights you might provide.



PS: The bright side - there's no more leaking coolant. [Although I didn't hear much noise from the old water pump - when I had it on the bench I could tell the bearing was shot.]

user 72902

You put in 3.3 gallons of coolant but did you put the same amount of water or less? The oil cooler is inside of the coolant and coolant is a much less effective heat exchange than water. As the water content decreases within the system your oil temps will increase and your water temps will stay stable. Not sure if this applies but I'd thought I throw it out there.

jchapura

I understand your question but I put less than that of distilled water because I knew that there was "trapped" pre-existing mix in the system and I calculated the likely needed amounts based on the total system capacity, a prior flushing with just distilled water, the amount withdrawn (twice), and the target of 50/50.

I've come to learn that it's a no-no to not pre-mix the coolant and water. It may take a few hours for the mix to become homogeneous. But does the lack of complete mixing explain the current higher oil temp?

Despite having used an Airlift, I need to learn how to "burp" the system, apparently.

user 72902

As long as the vent clip on the expansion tank was open the air tool should have evacuated all the air.

nk215

yeah, I think air get into your system somehow. Maybe when you switch coolant containers? The fact remains is that when your temp needle fluctuates, you have air trapped in the system, most likely at the thermostat housing.

I've not work coolant system in my 911, that was my experience with other cars.

jchapura

Thanks jkw911.

I did not open the vent clip while using the Airlift. Dang it. I do think I have some air in the system.

I do think that my coolant and water have not yet completely mixed. Apparently, pure coolant doesn't transfer heat at the same rate as water.

Can anyone point to a concise "burping" method?

jchapura

I have now burped the car twice (thanks Yves). I have captured some coolant temp data with a dongle and Torque Pro.

Does this chart look like it came from a car that has a low temperature thermostat installed in it?

motopix

How do you think a low temp thermostat works?

It's not unusual for the water temp to hit almost 200 (197 in my experience) before the fans bring it under control.

jchapura

I was focusing on the temp value at the abrupt temp change at ~4:33 (tstat opening? And not 160...) and then the average temp for the plateau of the curve (too high for a low temp tstat?).

LexVan

I don't think your coolant and distilled water have mixed thoroughly enough yet, since you introduced them in layers.

jchapura

Someone else has mentioned this too. I have about 170 minutes on the engine since the change-out. How many engine minutes do you think it will take for the complete mixing?

LexVan

OE Porsche water pump in a Porsche box?

jchapura

Not Porsche. A Pierburg pump in Pierburg box.

LexVan

There's your answer. I hope it does not have a metal impeller.

jchapura

It has a composite impeller. Are you suggesting its flow characteristics are sufficiently different from the OE to explain this issue?