I have a 1998 S70 T5, 180K everything has been great. Noticed an antifreeze smell in the car after about 5 minutes driving. I installed a new heater core.

Next day car is over heating. I had just put plain water in thinking to see if the heater core leaks. I thought that was the problem. I change it out with 50/50 antifreeze. So I am going home and after about 5 miles, all the sudden the temp gauge is going hotter. later I find a leak in the coolant line to the turbo. On the road again and the car is over heating about 3 miles, but no indication on the temp gauge. Now I am thinking thermostat. I change the thermos stat.
Test ride I don't go three miles and I see the temp going up, I get back to the shop just before it gets to the red.

No leaks, no milkshake in my oil, all the spark plugs look the same, no leaks from water pump. no bubbles in the reservoir until overheating, I went to look at a water pump at the auto store, seems to be a positive drive to me, a no fail pump? so ..... that's my goody....

 

How do you know it is overheating if the gauge isn't saying so?

Is the fan coming on?
Has the cap been tested?

 

First time, heard boiling noise under the hood. Second time, started running poorly, oil light flickering at idle, then antifreeze under car. Most of these time I was aware of problem and raised the hood, boiling noises coming from reservoir. the times I let it cool off reservoir was very low on coolant, like half a gallon.

 

...and my other two questions?

 

I'm thinking either bad coolant tank cap, or a big air bubble in the system that needs to be burped out.......leaning toward the cap though.