This is a long post, but it's a guaranteed puzzler if you read the whole thing.

I have a 2001 V70XC with approximately 35,000 miles on it. The vehicle loses coolant at the rate of approximately 1 pint every 2000 to 3000 miles, usually using a pint in about 2500 miles. We have discovered that this car has been in the Volvo shop for this problem at least 4 times in the past and it is currently in the shop for a 5th time. It has been there for over 2 weeks now with no diagnosis except that "we can't find the problem". It has also been examined at least once at a shop that is not affiliated with Volvo.

Here are the facts from the previous (original) owner as I understand them:

1) He bought the car at 2635 miles.
2) Somewhere between 4600 and 4700 miles, it first ran low on coolant and he filled it back to MAX.
3) He took it in for service at 7229 miles, complaining of a second occurence of coolant loss. (Volvo claimed it was a loose radiator hose.)
4) He took it in again at 9190 miles.
5) At 9347 miles Volvo replaced the cylinder head to cure the coolant loss.
6) The vehicle continued to consume coolant at the same rate as before.
7) At 24409 miles, the vehicle received service for coolant loss while it was in for 22500 mile service. Volve replaced the coolant reservoir cap.
8) At 24463 miles, the vehicle had been sold and was again on Volvo's lot for sale.
9) We bought the vehicle at 24738 miles.
10) By 27500 miles, I first found the coolant to be low. I filled it to the MAX line, thinking I remembered that it had been at MAX earlier when I had checked the fluids as we were looking at the vehicle before the purchase.
11) At 30021 miles, I took the vehicle in for idling roughly, being hard to start and coolant loss. They replaced an ignition coil (which cured the rough idling, poor starting) and claimed that the coolant loss was normal and if it continued, they'd take a look at it.
12) At 32977 miles, I took it in for coolant loss. Volvo was unable to locate the reason for the loss of coolant.
13) Shortly thereafter, it was serviced at a shop that is independent from Volvo to perform the 30,000 mile service, including coolant replacement. They were unable to find the cause of coolant loss.
14) It now has about 35,000 miles on it and it has been in the Volvo shop for over 2 weeks for loss of coolant.

Here are the troubleshooting facts as I know them.

1) The coolant loss has never subsided, but tends to be more rapid when the vehicle is operated for extended periods of time.
2) All hoses appear to be in good shape and are properly attached.
3) The water pump appears not to leak coolant.
4) The head replacement did not cure the loss of coolant.
5) The new coolant reservoir cap did not cure the loss of coolant.
6) The coolant system holds pressure when pressurized overnight.
7) There is no coolant in the oil.
8) There is no oil in the coolant.
9) There are no signs of dissolved exhaust gases in the coolant(according to the service adviser, but I'm not convinced the test was done).

Now, here's what I think is the biggest clue:

1) Open the coolant cap when the vehicle is stone cold.
2) Reseal the coolant cap.
3) Operate the vehicle for 40 minutes (drive to work).
4) Repeat step 3) (drive home from work).
5) Let cool overnight.
6) Let cool an additional 24 hours.
7) The cooling system still has what appears to be 8 or 9 psi on it.

What's going on? Where is the extra pressure coming from?

The service loaner which is a S80 does not maintain coolant reservoir pressure when the engine is cool. Try it on your own vehicle. Opening the coolant cap on your vehicle when it's cold. It should be a total non-event. No pressure, no suction, no nothing.

Does anyone have any ideas?