Best way to troubleshoot sudden cooling issue?

[butters]

My S50 was running really great for 2 weeks. Got it bled and wasn't worried about overheating. SPAL on low was able to keep her comfortable (in Portland the weather isn't too extreme, thankfully).

The other night, I went to pull out and clean the ICV in an effort to figure out why I'm smoothly idling at 1200rpm. In the process, I bumped the TB coolant line (I believe) which I noticed had no hose clamp and lost some coolant. Topped it off and figured it would be okay.

Next day it ran warm on the way to work. Returning home, it warmed up quite fast. Within a couple minutes it was nearly red on the needle. I pulled over, and it was steaming from under the intake, I believe at the TB. Cooled down, tried again and couldn't go a mile without nearly overheating. Upper rad hose was hot but likely empty or at least not pressured, while the lower hose was only "warm" and also felt empty.

I'm hoping that it's as simple as an air bubble that I introduced at the TB and reached the tstat which isn't opening as a result. How can I tackle this issue without pulling the tstat & drilling it... pour water in the rad hose(s)? As a last resort I may need to drive without a tstat for a bit. Any harm in that?

[dude8383]

When you topped it off, was the car OFF or ON?

[cabin]

If you didnt bleed it after topping it off you most likely have air in the system. I dont see any reason why you would need to drill a hole in the t-stat.

[jlevie]

It sounds like you didn't bleed the system after fixing the TB hose and it also sounds like there is a leak at the TB heater. Fix the leak and then bleed the system by:

1) Using ramps or a jack get the front of the car 1' or more higher than
the rear. That will make the radiator and bleed screw the highest point
on the engine and facilitate removal of air.

2) With the bleed screw open, add coolant until no more air comes out of
the bleed.

3) Leave the filler cap off, or at least loose, and set the heat for max
temp and fan speed. Leaving the cap loose will prevent air that's still
in the system from causing a "coolant fountain" once the engine heats
up. Start the engine and allow it to warm up to operating temp. As it
warms up occasionally crack the bleed screw to release any air and top
up the coolant as necessary.

4) Once the engine is at temp bring it up to 2000-2500rpm for a few seconds
several times. Then crack the bleed until no more air is released. At
this point the heater should be throwing lots of hot air, which
indicates that the heater core is filled with coolant. You may have to
repeat this a few times to get all the air out.

5) Drive the car a bit, allow it to cool back down, and recheck the
bleed for air. Over the next few days you may get very small amounts (a
few bubbles) of air out of the bleed screw.

[butters]

Done and fixed, my baby is back on the road better than before (thermally speaking).