overheating/loosing coolant

[SilverJester]

My car is overheating whenever I start boosting (so far every time I attempt to tune my car by making pulls on the highway). It has also started smoking what I believe is white smoke, but it's hard to see since it doesn't do it all the time, I've never been able to walk around to the back of the car and see smoke. It only seems to smoke at stop lights for a short while, but gets progressively worse the longer/harder I drive it. DD around town it doesn't overheat until maybe 4 or 5 days when I believe it finally begins to loose enough water to overheat.

I've done a compression test and the cylinders seem fine. I've also done a pressure test on the cooling system and it is leaking but I cannot tell from where. I'm completely out of ideas on what to do and.or check next...any ideas?

P.S.
I recently installed some new turbos and supporting mods before this problem began. Also fans are hot wired on HI.

[Fletch]

If it has overheated I would be a bit leery of a bad head gasket.
How bad did you cook the engine?
Have you checked the oil for coolant in it or the coolant with oil in it?

The smoking at a stoplight sounds like the infamous Valve Stem Seals... there are write ups on a few sites for this procedure. I am almost ready to tackle mine, and I will make a write up, but it will be on a N/A.

[Polygon]

Check for hydrocarbons in the coolant. I'm betting you've blown a head gasket.

Let's get something straight though, that's steam, not smoke.
</pedantic>

Now, where's the steam coming from, the exhaust? Or is it coming from the engine bay, or both?

[SilverJester]

lol, ok the steam is coming from the exhuast, nothing from the engine bay. I originally thought it was a head gasket too, but according to the compression test it should be fine as should the valve stem steals.

[fastnelson]

Check the radiator
check the thermostat
It can be an little thing before i say you have an head gasket problem but yet i would take the heads out to check it if the 2 above are ok.
The smoke is something else , sound like bad valve steam seals and the overheating helps that.
Is difficult to give you the right answer from an Internet , just thoughts.

[SilverJester]

Appreciate the input guys, but wouldn't a compression test read low on 1 or more cylinders if it was either a head gasket or VSS?

Compression test results:
front cylinders (pass to driver side): 140, 135, 140psi
Rear cylinders: 145psi across the board

Also if it matters I've been running straight water since it keeps overheating and loosing coolant. I plan o switch back to coolant/anitfreeze/water mix once i figure this issue out.

I forgot to mention that the thermostat has been changed already as well as the radiator cap.

[Polygon]

I would still check the coolant for hydrocarbons to be sure. If the coolant comes back clean, the head gaskets are fine. Plus it's cheap to have a shop check for it.