99 GMC Suburban, 2 wheel drive, 1/2 ton, 350 ci will not reach operating temberature. When new, it ran about 190-200 degrees, now it runs at about 150-155 degrees. I have replace the thermastat, and the temperature sending unit, still runs cool. I recently replaced the intake manifold gasket to fix a water leak at the back of the intake. I thought this wold fix the problem, I had the same thing happen on a 92 GMC truck. The cooling system is water tight now, no leaks, still the same problem. Do you have an answer?
Tags: 99, GMC, Operating, reach, suburban, temberature, wh, wont