Running ZZ4 in 79 and have a question about the sending unit for water temp. Original sender is 1/2npt on drivers side head. ZZ4 uses 3/8 NPT on head. Is there a 3/8 sending unit that will work with the 79 gauge? Currently have new sending unit in manifold, not sure it is correctly calibrated for my gauge, car runs 220..........any help appreciated. :confused:

 

I had a similar problem running vortec heads on my 80. I visited my local hardware store and fabricated an adapter to fit for about $1.50. Actually, I had to use 2 adapters inline to make it work. Cut of the end of one adapter to allow the sending unit tip full exposure to passing coolant. You really don't want to use any other temp sending unit then the one made for the 79 as you will get incorrect temp reading. Trust me, I know from experience.

Jim

 

I was looking at my new ZZ-4 (still in the crate) last night, thinking about the same problem. There looks like there is a 1/2" pipe plug up on the front of the intake manifold, near the thermostat housing that would fit the old style temperature sender.
Recently ChevyHighPerformance mag did a test on sending unit location and temperature variations. Initially there is a difference between the head temperature and the manifold temperature (about 5 or 10 degrees) but once the thermostat open completely and a good flow is going through the cooling system the temperature difference is barely noticeable.
I'm going to put my old sender in the manifold, and the sender from an 81 vette in the head, this way I should be able to tell how close the temp senders are to each other. The passenger side head will hold the sensor for my Spal fans.
Good Luck.

 

I put the sender right next to the thermostat. The hole there is 1/2 inch and the original sender fits perfect. I had decided to buy a new sender from NAPA and it was around 50 degrees off (reading high). I ended up using the sender from my old motor since it worked and read correctly.

Mark B.

 

When I switched heads, I put my original sensor in a pot of water on the stove and took ohm readings at various temps (190* - 210*). Then, I went to NAPA and looked through their book which had the specs on temp sending units. I could not find one anywhere near the original reading. I then bought a lat model shark ('82?) sending unit. I stopped by Radio Shack on my way home and bought some resistors. Back at home, I put the new sensor in the water and put some resistors in parallel to make it match my original sensor. Be warned, though, that if you do this the sending unit is only accurate for a small range. In my case, this is between 190* and 210*. I think my temps reach 140* before the needle even moves.

 

This is what I did for my ZZ4 installed in my 1980.

The GM Parts store told me to look for a 1994 truck or equivlant with a single blade sending unit. The 1994 or above has the smaller sending unit, and will work for the ZZ4. I went to Orielly's and talked to a good friend of mine. He found a sending unit from a GMC 1994 (I believe) single blade unit. I think it was from a V-8 block. I knew it would work, as I went and looked at my 94 truck, and it looked like it would fit.

It works fine, and seems to be calibrated correctly.

BTW, mine runs around 220 also.


[Modified by kgraumann, 12:30 PM 8/6/2002]

 

Thanks for the replies.........what I think I am going to do is geat the original sending unit for the 79, and run in in the manifold. Shouldnt the temp be 180 (using 180 thermostat) in the block once the temp stabalizes, within a few degrees?

 

In theory, the temp should be a little higher than the thermostat setting. But since this depends on a perfect cooling system with adequate air flow through the system at all speeds and traffic. Since a perfect cooling system is probably impossible, then I suspect that your temp is going to run higher than the setting of the thermostat. So if you have a 180 degree thermostat and are crusing at 40+ mph (when your air flow should be as much as the fan would pull) in a temperature of 72 degrees or lower, I would suspect that your temp would hover between 180 and 190.
Sustained idling in heavy traffic with AC on and temps over 90 degrees will certainly cause the radiator to be less efficient. Then you start seeing temperature creep. If your cooling system is in good shape you should expect temps to creep up to the 220 mark. My owners manual says that 210 is normal operating temp for all 69 sharks. But if the temp goes past 220 for any prolonged period of time, then pull over and let the car cool off.
In a very warm climate, Florida, Texas, Arizona etc. I'd suggest 75% distilled water and 25% anti-freeze. A bottle of Redline Water Wetter won't hurt either. Check and make sure you radiator seals are all in place, your under chin air dam is inplace and your radiator hoses are in good shape (a collapsed lower hose can mess you up!) If you car is in good tune, with a clean radiator (with all the seals etc) you should not have any overheating problems 99% of the time.
But get stuck in traffic with your AC on will cause the best cooling system to give up the ghost!