One of our '90 ZR1s started using coolant. It was dripping under the firewall in back of the passenger front wheel. I checked the area around the heater hose conditions and everything was dry. Checked the passenger rug and it was dry. That ruled out the heater core but I could not see how it could be anything else. Then I thought that maybe GM got smart and vented the heater box to the outside! That would be almost as good as moving it to the other side of the firewall and let it leak on the ground. Anyway it turned out to be the water pump and the fan was blowing it back to the firewall but I did not know it and we tackled the heater core.
Followed the Helms manual to remove the dash but two things came up worth passing along. One is that there is a plastic duct going across the front of the heater box with a snap on short duct going into the heater box. This duct goes on behind the main console which I had no intention of dismantling. I was tempted to cut the duct by the console and get a rubber tube to reconnect it later but restrained myself from doing this due to the many years (since 1980) of NCRS training. So I unbolted the heater box and pulled it out from behind the duct while pulling out on the duct. This separated the snap on duct that I did not know was there. Next time I will separate it first. The other thing to mention is that there are two rivets that look weird and not like rivets. These I pried up with a screwdriver. Even if I knew they were rivets, it would be hard to get in there to drill them out. (Bad design - GM should have spent a few cents more and used bolts. They could have use rivets to hold a nut plate on for the bolts.) I did not have the time to redesign it so I left the rivets out when I put it back together.
Hint on putting the heater box back together : Slip the heater box cover back in place but don't bolt it back on. Take some twine and tie it to the short duct that goes into the heater box. The twine needs to be long enough the be pushed down and off of the pipe after it is snapped into place. Put the tube in the box with the twine coming out over the duct. Get the fingers of both hands around the duct and pull the twine until you get the snap end of the inner duct in place. Put the key on first and snap the two together. Push the twine off the end of the tube and pull it back out of the box. I used a piece of spring steel to shove it off the end of the tube. This maneuver should not take more than 1/2 hour to get the tube snapped in place. P.S. I had to take the dash apart three or four times before I got it together right.
All was not in vain as the heater core had a pin prick in the middle and a v-shaped stain but had not started to leak out of the box yet.
The water pump is another story!
by Jim Blanchard
Work Assisted by Wells Blanchard
Article edited by Kay Blanchard