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Z was running hot - Notes on how I fixed it.


Aug 4, 2005
Castle Rock, Colorado
90' Black ZR-1 #1723
This probably isn't a new issue to many of you, but I thought I'd share a few comments on how I resolved my hot running Z.
After owning the Z for a few weeks now I noticed that she ran on the hot side in traffic and particularly on very hot days with temps over 95'. Last week she almost overheated on me on a 103' day:willy: . After researching this site an the other ZR-1 sites out there I knew what I had to do. (Isn't the internet a great thing!)
As usual, I jumped in with both feet and pulled the radiator, hoses and t-stat out of the car. I found what all C4 owners eventually find, a clogged radiator and a thermostat on it's last legs. The hoses were marginal so I decided to replace them while I was there. You can find the "how to" elsewhere but here a couple of things I learned:
Those six little 7mm screws that hold the front of the shroud are a bear, but with patience you can get to all of them for removal. Removing the horn and air pump make getting to the upper passenger side screws much easier. Remember to move to spring thingys that the screws screw into, from the shroud to the part of the housing that stays in the car. This way you can put the screws in from the inside when reinstalling the shroud. There's alot more room to work from the inside.
Yes, you can take the radiator shroud out, without removing any of the A/C or Oil cooler lines, just lift the driver side while standing on the passengers side and work the shroud out from around the hoses. It comes out and goes back in with a little effort.
Removal of the hoses and t-stat housing is pretty straight forward except for the lower radiator hose. I found that by removing the fans with their housing, removing the serpantine belt and holding the belt tensioner back with a long half inch breaker bar, That gave me reasonable access to the hose clamp that attached the lower hose to the block. When installing the new hose there, just use a standard screw type clamp, it's much easier to install than the original type.
If you get this far and you haven't replaced the serpantine belt in some time or maybe it's never been done, go ahead and do it now. It dosn't get any easier. It's cheap insurance. They are available from any parts store.
I used a 180' t-stat from "Stant" #14068 as recommended by many and a set of new hoses from "White Racing". Kurt got them to me last minute in good order. (thanks Kurt)
Although the radiator cleaned up well, I ended up installing a new one. On final inspection of the original radiator I found cracks in the reinforcing webs around the lower outlet. I've read about this, again better safe than sorry, I got an new GM radiator. E-bay $149 shipped. Half the price of the local dealer.
I also added a Haibeck chip (needed an excuse) but now the fans turn on earlier and at the same time, plus a few "other" things.
Everything else went back together normally. I found "Low Silica" coolant at my local CarQuest store (their brand) a nice to have for an all aluminium engine like ours.
Now that everything is back together she runs cool as can be. Before she was in the upper quarter of the temp guage, now, right in the middle.
Thanks forum, for all the info..hope this gives a little back.

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