hi guys can anyone help ive an 88rs turbo and ive tried a new pump thermostat and temp sensor and even gauge to no avail when running at 3000rpm the heater is hot and the gauge reads bang on the n ,the fan cuts in and it doesnt go into the red when you pull up the heater goes cold and within a minute the heater goes away to verycold please help ,ps ive also tried flushing the system different coolant strengths bleeding it.it has a hairline crack in block behind turbo but it not wot id say leaking just slightly damp any of you guys had something similar,