After putting 1700 miles on the odometer I figured it was time to see if I could fix the AC leak before summer was over. I took the GTM to the local shop that tried charging the AC in my garage last summer with the hope that they could use their ‘sniffer’ tool to find out where the AC leak(s) were. Fortunately, the tech was able to locate the leak in less than 5 minutes. The leak was at the low side service port connector to the AC accumulator/dryer. I had my fingers crossed that this would be where the leak would be, as many other builders that have had AC leaks had their leaks at the same connector.

The cause of the leak was an insufficient o-ring. The o-ring supplied with the vintage air kit is one size too small. Any builders out there that haven’t gotten this far yet – make sure to check that o-ring. With the new o-ring in place the system held vacuum and charged successfully. I got in the GTM and cranked the AC and was greeted to a faceful of 2 years worth of dust, but it worked! This was a great relief, seeing the AC fire up and work properly.

When I was tuning my motor last year to get it running properly I had set my “AC target idle RPM” to 1100 and the car seems very happy at that RPM with the AC running. Took it out for a 35 mile drive in 80 degree weather and the car never got any warmer than it would have when the AC was not working. At stops it actually runs/idles smoother with the AC on.

Cliffs: AC works great and keeps the car nice and cool. Check your accumulator low-side service port connector o-ring!

Last week while cruising some back-roads in the GTM I started to smell coolant. Not the greatest smell when you are out in the  middle-of-nowhere and it’s blazing out. I came back into town keeping a close eye on the coolant temp and temps were still fine, so I took it out on some more back-roads with temps still fine, coolant still stinking, and eventually got it back home and on the lift. Suspicions were confirmed when I saw that the GTM had created a slow drip of coolant seeping through the underbody aluminum under the engine.

I took the underbody panel off and did not see anything out of the ordinary and assumed that the previously mentioned super slow coolant leak I had at the thermostat/steel hose connection was just seeping again. I then noticed some dirt on the water pump-to-radiator steel hose that runs in front of the balancer. Upon wiping the ‘dirt’ off I was sprayed in the face with coolant. Nice! Apparently the steel hose had chafed on the balancer somehow and it created a pinhole in the hose wall. Fortunately, I had dropped in some ‘stop leak’ tablets into the coolant last week and that stuff clogged up the hole (hence the ‘dirt’ on the hose). I stopped the leak with some strategically applied paper towel and went to the local auto-parts store the next day and ordered new hoses to replace FFR’s supplied steel corrugated hosing. I ended up picking up Gates molded coolant hoses, part #’s 20827 and 20893, as per some recommendations from the forum.

To get started, I removed the interior engine cover and pulled the rest of the underbody aluminum off (tunnel pieces, at least). I started on the thermostat hose first and loosened up the 1.25″ hardline that goes to the t-stat steel hose. After draining what coolant I could from this side (about 2 gallons) I pulled the hose off of the t-stat and connected the Gates hose (20827). This Gates hose is a 1.5″ hose so this meant that it would not fit the 1.25″ hardline without an adapter. I mocked up the connection to the hardline and set to work on the water pump hose. This side dumped another 2 gallons of coolant, and then I disconnected the steel hose from the water pump. The Gates hose for the water pump (20893) is a 1.25″ hose, so it fit the water pump fine, but of course would not fit the 1.5″ hardline that it had previously connected with via the steel hose+adapter. As a result, I consulted with the forum again and decided to swap the hardlines side to side (not changing any connection paths, simply swapping the 1.5″ hardline with the 1.25″ line). This allowed the Gates hoses to fit up perfectly – 1.25″ from water pump to hardline, and 1.5″ from t-stat to hardline. No adapters, four less points of leakage/potential failure. The Gates water pump hose works quite a bit nicer than the corrugated hose as it clears the frame member in front of the motor, eliminating any possibility of it chafing on the balancer again.

With the hoses reconnected and hardlines secured again, I was able to dump almost 2 gallons of coolant back in. I jacked the front of the GTM up and let it sit overnight. The next day the coolant level dropped a ton and was able to get another gallon in. I started the GTM up and let it idle for a few minutes, then shut it down. This got coolant circulated and pushed a bunch of air out and allowed me to get the last gallon of coolant I had pulled out poured back in. I then idled the car for 20 minutes or so (took that long to get to its standard 210 degree operating temp in a 95 degree garage) and it showed no signs of overheating. Fans were coming on, going off, temps held solid. Good stuff.  Shut it down and topped off the surge tank again with another quart of coolant/water.  No leaks. This fix ended up being much less of a headache than I had anticipated.

Buttoned the car up and got the car out today for a hot (102 degrees in the sun) 20 mile drive with some spirited throttle work here and there and all systems checked out. Temps never went past 210, and it seemed to be running cooler by bit, even.  This is how FFR should have the coolant lines setup in the manual from the get-go.

Today I prepared the diffuser for the installation of the louvers. The louvers will greatly increase airflow through the engine bay, keeping the engine quite a bit cooler. To get the diffuser ready I first had to mount the diffuser on the car, find its center, and mark the inside of the diffuser for the body edge so that the louvers do not overlap the body where the diffuser mounts to. Once that was done I removed the diffuser and set the louver assembly in place. Once I had it where I wanted I drilled out all of the rivet holes, cleckoing it as I went. Holes drilled, the louver assembly was removed and the diffuser was flipped over and the louvers were re-clecko’d on the interior side of the diffuser. I then etched the inboard perimeter of each louver onto the surface of the diffuser to prepare it for cutting. With the perimeter scribed, I cut out the louver holes while leaving the scribe marks intact. This allows for the installation of the louvers on the interior side of the diffuser while keeping the aluminum edges hidden by the diffuser. Once the diffuser was cut I clecko’d the louvers in place and bent the fins up to match the angle on the strakes. The strake ‘ears’ had to be bent to sit flush on the diffuser.

At this point I need to pull the louvers off again and take them for powder coating. Afterwards, I will be able to rivet them in place and mount the diffuser.

I received my harness bar earlier in the week and after having it powdercoated, I was ready to install it.  The harness bar (made by North Racecars) uses 2 mounting bolts on each side – one through the rear wall and into the 1″ frame the wall mounts to, and the already-present seat belt mount. I set the bar in place using the seat belt mount bolts, then drilled out the frame through the rear wall. Rivnuts then had to be installed for the harness bar bolts so I had to remove the fuel tank covers, engine covers, and one of the upper cockpit walls to get the wall out. Unfortunately, one of the rivnuts stripped out when removing the rear wall so I had to carefully cut the bolt head off to get the wall out, then cut the rivnut out. With that out of the way, and a good chunk of time wasted, I set in the new rivnuts and reinstalled everything. During the reinstall a rivnut in the wall for the passenger fuel tank cover stripped out, but I was able to get the bolt out and re-thread it with a tap. Good as new.  The harness bar, with the extra rivnuts in place, installed in about 30 seconds. Nice quality piece.

After doing the harness bar I riveted the defrost ducts in place on the center console.

Tonight I tackled the passenger suede. This side went on alot easier than the driver’s side suede. Only two obstacles to work around (the footbox frame tube and the ebrake), and simple angles allowed the work to go fast. Once the suede was on I cut out the vent opening.

After the suede was on I finally mounted the AC blower motor into the passenger footbox and tested it out – works good!

Since getting the cooling system filled was pretty annoying, and the FFR manual doesn’t help AT ALL, I thought I would post a step-by-step as to how I did it. Thanks to Henry over at the FFCobra.com forums for helping! 

Before I get started it helps to know that you will be using 4.5-5 gallons of coolant.

1. Fill surge tank – should be able to add almost a gallon of coolant to it. Leave the cap off the tank.

2. Disconnect the upper radiator hose on the water pump.

3. Disconnect the bigger of the two ‘smaller’ hoses on the passenger side of the radiator. The hose you want to disconnect runs to the surge tank.

4. Disconnect the two steam vents at the top of the heads on the engine. You only need to open the vents on the belt side of the engine.

5. Start pouring coolant into the water pump hose that was disconnected previously in step 2. When coolant starts overflowing out of the radiator connect the small hose back to it.

6. Keep pouring coolant in until coolant either comes out of the steam vents, or it comes out of the water pump port that is open (from the hose disconnected in step 2).

If you cannot get fluid to come out of either location without the surge tank overflowing, or just cannot get any more fluid in at all, you have an air lock.  Jack up the front of the car, reconnect the water pump/radiator hose and run the engine at idle (still with the cap off the surge tank and vents open) for a minute, then put the cap on and get the temperature up to 210 by revving the engine in intervals. Shut the engine off, carefully remove the cap, and disconnect the water pump hose from step 2.  You should be able to get more fluid in – if not just let the car sit over night with the front end raised, surge tank cap off, vents open, water pump hose off and elevated. Air will work its way out. 

Repeat step 6 until you get fluid to come out of the water pump outlet or the steam vents. The first time I went through this step I had 4 gallons of coolant in the system. It took a few repeats of this step to get the last gallon in.

7. If coolant comes out of the steam vents connect the water pump hose again, and reconnect the steam vent covers/surge hose. 

If coolant comes out of the water pump outlet then top off the coolant that is in the water pump/radiator hose, and carefully connect it back to the water pump without spilling too much. Coolant should now shoot out of the steam vents. 

Run the engine like you did in step 6 and let it sit with the vents, water pump hose, and surge cap off for a few hours (or overnight like I did). If the coolant drops in the surge tank this means more air was released. Top it off again via the water pump hose. 

Repeat this step until the coolant no longer drops in the vents or surge tank while sitting. To ensure I had the coolant topped off each time I injected coolant with a baster into the steam vents until it overflowed. When it finally stayed at the top, and the surge tank didn’t drop, I knew I had the air out.

8. Top off the surge tank as needed and run the car for a while and observe the coolant circulating once your thermostat opens (you can see it circulating at the bottom of the surge tank). Both hardlines should be warm to the touch. If one is hot and the other is cold then you still have an air lock – go back to step 6 or 7.

Today was pretty exciting. Before doing anything I checked the coolant from the other night’s fill; it had settled a quite a bit (ie: air pockets released). I decided to idle it for a bit and see how it cooled (or not). Before idling I threw on some wheels and finally got the GTM off its stands.

Since it was idling, and on the ground now, I decided to see if reverse worked. It didn’t. I realized it was because I didn’t set the gate cable properly to allow the cable to pull reverse, so I fixed that. With reverse fixed I backed out of the garage into the driveway, let it idle outside for a bit, then pulled it back into the garage.  It felt pretty good to be able to drive it a few feet! However, there is still air in the cooling system, as the temps got too high again after idling for about 15-20minutes.

With that out of the way I let the coolant settle for the afternoon and came back tonight to add more coolant. I added more the same way I did previously: disconnect the upper water pump hose, open the steam vents, open purge tank cap, and dump coolant into the water pump/radiator hose. Tonight I was able to add in quite a bit and am now at over 4.5 gallons (shouldn’t take more than 5 gallons). There are probably a few air pockets left to get out, so I will let it sit overnight again.

Also did some troubleshooting on the throttle body. With some adjustment I was able to get the car started with it (before it would throw codes and would only start with the scanner disabling them), however it would not idle. This seems to be a manufacturer defect, and not something I can fix, so a new throttle body hunt begins.

I also installed the exhaust.

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.

Since I am stumped on the engine/throttle issue I started on installing the skid system. This will protect the underbody of the car, as well as the actual body, from speed bumps, ramps, etc. Each skid bar (8 in all) is attached to the frame using tapped 10-32 holes. The process is painstaking, but the end result is worth it.  I attached the front four skid bars tonight and will tackle the rest once the engine is running properly and no leaks are found.

After working on the skid system I loomed up the oil pump wiring, and attached the hard coolant lines to the frame.

Tonight the clutch line was plumbed/finished and attached to the clutch slave. I need to get some nuts to mount the slave to the trans still.

The coolant hosing is now all secured. I replaced the last corrugated hose clamps with the heavy-duty ones I am using and doubled up the extra clamps around the hardlines.

The serpentine belt now fits perfectly. It did not fit previously due to the ‘wrong’ balancer I had on.

Some random issues that need to be resolved:
– Figuring out how to connect the fuel rail to the fuel filter output is still in the works, but Josh and I have a plan.
– I need to figure out a better way to protect a segment of the main wiring loom from header heat (it sits about 1-1.5″ away). The portion of the heatshield I made out of 2″ loom touched the headers there so I removed that portion.
– The rear window aluminum piece will interfere with the intake manifold…probably going to have to cut a pocket out for it.