07 GT Coolant Overflowing Issue! HELP!!

Ok I'm at my wits ends here. I have no idea what is causing my car to be a pain in the ass lately. Lets start from the beginning.

 

Last summer late august (MN 80-90 degrees High humidity) I was out driving around and my temp gauge jumped up to about 3/4 it seemed to be correlated with how fast I was going. 80-85 was high maybe a bit more than 3/4, 2-4 white lines below the red marks. If I slowed down to 60-70 it would drop but would still be slightly above 1/2 way. I drove on a 160 mile trip and it was very hot and muggy almost all the way temp gauge stayed about 2/3 to 3/4 up. As soon as I hit some rain and the temp dropped my gauge dropped. I attributed all that to the weather, but checked my coolant when I got home and it was a bit low so I topped it off and it was just fine from then on out.

 

Put er in a snowbank good this winter and cracked some stuff up pretty good, new radiator was put in and new thermo all that. No issues at all all winter.

 

Jump to NOW the past 2-3 weeks have just been a bitch with this car. I noticed my temp gauge started to climb stopped check for a leak and i saw some dripping on the lower rad hose thought it was the hose at the radiator was loose and seeping a little. Got on the highway temp dropped. Continued this way all every trip all times of day until today. I started checking coolant each night when i got home after it cooled down it started taking a little more and a little more. Just kept adding water as I don't want to be spending $12 every 4 days for a gallon of coolant.

 

So this is whats happening now:

I'll leave the house in the morning cold engine, get on the highway temp is fine all the way to work, no stop and go, (30 miles). I will get to a stoplight and temp is fine, when i start to accelerate the temp goes up. Stop again it stays, accelerate again it goes up. It will always climb to the top white mark never go above. I will get to work and check and the overflow tank is very full and around the cap is wet and my fan by the tank is wet. (Tank is filling up and overflowing)

 

Now I can park the car for 20-30 mins and the temp gauge will be back down to 1/2. I will start driving and again, stoplight its fine upon acceleration temp goes up. NOW! i can sit at a light and rev my RPM's up to about 2k-2.5k which will start to bring the temp down, if its a long light i can do it and make the gauge return to 1/2 again. Get on the highway and temp is just fine at 40+MPH

 

The coolant was vacuuming back in when cooling, replaced Rad cap and it vacuums back in now.

 

I think the tank is overflowing on the first drive of the day, then creates and air pocket, the air pocket then causes the temp gauge to go up and down depending upon engine speed (not necessarily how fast im going because I can make the temp drop down sitting still)

 

WHY IS THE COOLANT BOILING AND OVERFLOWING!!!!???

 

I've replaced the thermostat with a new oem one, I've flushed the coolant and radiator this week brand new coolant, ran water from the hose through the radiator for 10 mins. New radiator cap this week. No hose seems to be too worn, can't feel any collapsing from any of them. Both upper and lower are warm after driving 15 mins.

So have you had the head gasket tested.

I forgot to mention that. I rented the block tester from Autozone when I first noticed it and checked it, there was no indication of exhaust gas in the coolant/radiator.

 

PS: No oil or milkyness or in the coolant.

Fans in good working order? Possibly bad water pump?

Fans work perfectly when car starts to get hot with or without the AC on.

 

Waterpump was replaced at 95K (Car now has 145K)

No HC's, I would have guessed HG.

 

Is there any possibility of a crack in the head ?

 

We need to look at what the possibilities could be.

 

Radiator was replaced...May be have the system pressure tested.

 

 

Water pump just pumps, it either works or it doesn't.

 

T'stat must be opening, could it be working intermittently ?

 

First is thing to do, burp the system.

My guess would be something wrong with the impeller on the water pump. This isn't something that you think would fail but it could cause similar symptoms.

In early 2000 Volkswagens, they made the mistake to use water pumps with plastic impellers.. After several years the plastic would break apart. The car maintains normal temperatures when it is running at 30+MPH but as soon as you come to a stop the temperature slowly starts to increase until the coolant gets too hot and overflows. As long as the car maintains speed the cooling air seems to be enough to keep the temperatures normal.

 

Since you flushed the system, replaced the thermostat and you say there are no hydrocarbons detected in the coolant, the water pump seems to be the only thing left to check.

 

When cool, are both the radiation and coolant tank over the turbo full?

Water pump was replaced @ 95k replaced with a brand new OEM

 

I'm going to answer that with a NO. Everytime I drive the car more than 20-30 miles I loose coolant. I don't think I am burning it, it's usually spilling/boiling out of the radiatior overflow tank so when it gets cool there is no way it can still be full, to tell.

Still gonna go with HG. The only way that it pressurizes the system to overflow it is with exhaust gasses. Have you only tested with the Autozone tester? Take it to a shop --dollars to donuts says that you've got a leaky/bad HG.

Well...... I redid the block tester from autozone. The blue liquid turned yellower than my pee on a hungover Saturday morning! Motor pull this week... Woooooo like I didn't have anything else to do! Haha

So first time block tester stayed blue, and second time it turned dark yellow with no other changes?

 

Are you positive you didn't draw coolant into the tester the second time? I only say this as I had a mechanic do a block test on my car and the liquid immediately turned yellow. He then drained the coolant just a bit and did another test, this time, no change in color at all.

 

Another time, another mechanic, he immediately came back and said HG's were toasted bad. I asked him to try again and be as careful as possible to make sure no coolant is being drawn into the tester, which pissed him off. He came back 10 minutes later and sure enough, he had drawn coolant the first time. He said he wasn't able to get the tester to turn yellow again.

 

Then again, I've been dealing with this issue (similar to yours) for months now, and still no HC's in my coolant

Wow, this sounds very similar to the problems I am having with my 2007 Outback XT.

However, my temperature is very stable no matter how or at what speed I'm driving.

 

Any breakthroughs? Has anyone figured out what could be causing coolant overflow other than HGs? I've had my block tested and sniffed numerous times and haven't found a leak.

Ended up just pulling the motor and doing the Headgaskets. Had the heads decked and reinstalled and it's all good now.