The GTM Supercar Build Log

Coolant Fill, Underbody, Throttle Body Troubleshooting

With the front skid bars in place I finished securing the front underbody panels in place with some self-tapping stainless screws. This will make removal of the underbody easy in the future, if needed.

After that I decided to fill the coolant system. The GTM takes around 4-5gallons of coolant, and the surge tank itself holds around a gallon of coolant. I had already filled the surge tank previously, as per the GM coolant fill guidelines. The GM procedure wants you to run the engine up to 210 degrees in cycles, so I had to hook up the coolant temp gauge first (easy). I popped the cap on the surge tank and idled for a minute, then got the temps up to 210 degrees. At this point the engine started to overheat (took about 10 minutes to get that hot just idling with some revving), so I shut it down. No coolant was being pulled into the system (air lock). To try to get the air out of the system I jacked up the front end of the car, opened the vents on the heads and popped the top radiator hose off of the water pump (not the hose going into the thermostat). I hoped gravity would suck the coolant in and get the air out, but no joy there. I decided to force the air out by dumping coolant (a 50/50 water+antifreeze mix) into the radiator hose I just removed from the water pump. To ensure that air could escape, I pulled off the radiator hose that runs to the surge tank. After a few gallons coolant started coming out of the radiator (good), so I capped that hose and continued filling until coolant started coming out of the steam vents. Capped those off again and kept adding coolant until all the air was out (the surge tank started to fill up). I then reattached the radiator hose to the water pump. I will cycle the engine later to get any remaining air out. Also, the cooling fans worked as they should, so that is one less thing to worry about.

After filling the cooling system I tried troubleshooting the throttle body issue. I removed the GTM throttle body TP sensor and put that on the Z06 throttle body and the gas pedal still worked. I then swapped the throttle body motors and still got the pedal to work. That tells me that the problem resides within the throttle body itself.

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