Car = 1991 745T

Replaced my old, cracked coolant expansion tank/bottle with a used one from local Volvo mechanic. Both caps are rated at 150 KPa, but have different threads. Now that the system is holding the pressure that it should, there is a trail of coolant down the driver's side, rear of the radiator after it cools down. Also leaves a small puddle by morning. Did not have this problem with the old, cracked expansion tank.

With either the good tank or the bad one, the temp gauge reads the same. So, I was wondering if I could sort of put off having to diagnose and fix this now (very bad time for me) by simply putting a 100 KPa cap on it until I am able to fix it right.

I know the turbo cars, like mine, have a thermostat that opens at a higher temp then the normally aspirated ones, but wouldn't 100 KPa work? Just for a while?

I feel kind of between a rock and a hard place because I really don't like running an old cooling system at pressures as high as 150KPa, but, on the other hand, have extensive natural/physical science edu in college, so know why the Volvo engineers specified the higher pressure cap on the turbo. Keeps the coolant from boiling off at the higher temps the turbo operates at.

Still, have any of you run a B230FT with a 100 KPa cap and had success with it?