1998 s70 overheating..help!!!
I have a 1998 s70 2.4 turbo(150,000 miles). The problem with the overheating is that the engine purrs (great boost from the turbo, also), but after approx 30-40 minutes of highway driving the needle on the dash get's just below the red zone and when I open the hood the resorvoir is spewing out coolant(boiling). Just recently(within the last 3 weeks) I replaced the thermostat, waterpump, timing belt, some new hoses,had the radiator rodded out and pressure tested (all good), flushed the system twice, lower radiator hose not collasping,did a head gasket test using a tube filled with blue fluid and fitted into the resorvoir with a line hooked up to vacumn and the fluid did'nt changed color which they say isn't any exhaust leaking from the head gasket. The blue would've changed to yellow. The test fluid was brand new, also. I've taken this car for drives(4-5 times recently) at highway speeds and the baffling question is "why does it start overheating at the 30-40 minute mark everytime!!!!! The thermostat was checked when I dipped it in hot water and it opened and closed perfectly. The fan works good.
One thing of note: I did use a head gasket sealer about 3 month's ago and when the radiator was serviced they told me it was 40% clogged from either a radiator seal additive or the head gasket sealant.
I'm very frustrated and would appreciate any feedback. What else can I do?