Introduction and Overheating (long)

[ChattanoogaJSB]

I lost all of my first lengthy post, so I'll keep this short and try and add only what's necessary. I'm sorry it makes for a less congenial introduction.


91 ZR-1 was bought new by my friends father and driven 7K miles in the first two years. Sold, found again two months ago by my friend and purchased with just about 1K miles more. he had it serviced including new green coolant (but no idea if it was truly flushed), we drove it home 2,800 miles from Oregon to Tennessee in four days. low on power, shop had done three bad secondary injectors but not tested the primaries. I found four bad primaries ohm testing the ecu plug. all injectors I have now done with Accel, which totally restored the power!



On drive in flat country car would not run over 149 mph on a "closed course" in fourth or fifth but did not overheat at cruise. First mountain pass- overheated to 7/8 gauge, when we stopped. This was only when we were pulling uphill, but only going normal speeds. Downhill and flat were fine, temps restored to normal (about 1/3 of temp gauge)



Note when it got hot the overflow was simply ambient temperature and no change of level. Overflow still never seems to move and we have tried two caps.


swapped thermostat with a NAPA unit, but new and old boil-tested fine.


Fans come on. Used registry member scottfab method to refill (thank you!) taking off throttle body coolant line on drivers side as I filled to top.



both intake hoses will run 210 degrees with the fans on idling, system seems full. coolant looks clean. As soon as you ask it to pull a grade the temps go over half to 3/4 and will eventually go to 7/8.


My thought is that the radiator is probably flowing very minimally, having sat with (the orange?) coolant in it for possibly many, many years at a time.


can anyone help give me any other ideas? should I pull the radiator and have it cleaned or can i try and clean it in place?



I'm a regular on the CF but new here- I am not afraid to work on the car but I am trying now to get a little group consensus. I've got a '64 coupe that I rebuilt after a semi truck hit me, have had a couple of 69's and bought an 09 new. I also had an Lt-1 powered 95 Firehawk.


My friend has been a lifelong Porsche fan (as was his father) and I am desperate to make his ZR-1 the "better car" I know it can be!


Thank you in advance for any advice!


Benton

[ChattanoogaJSB]

Will try and post pics mid day, just to show off the car.

[grahambehan]

first thing to check would be debris between the AC condenser and the radiator, they like to collect garbage, leaves etc.
Graham

[Ccmano]

Benton, welcome to the addiction! Sorry to hear of your troubles. You came to the right place. I had to read your post a couple times to get a clearer picture of what is going on. It sounds like the car operates relatively normally until a large load is placed on the engine. I take it replacing the thermostat changed nothing.

Just to eliminate the obvious have you looked in the air intake area ahead of the radiator stack to see of there are any obstructions like leaves or a plastic bag? These cars act like vacuum cleaners and suck up all kinds of crap.

Next, it would be good to get more accurate temperature readings, the dash gage is not reliable. Do you know how to get temperature reading on the AC display?

1. Push and hold up and down (each side of Fan Control button) until you get zeros in display on left.
2. Then push up button to right until you get to 16 in the display.
3. Then push center fan button to read digital coolant temperature in degrees C continually in the display until you hit the temperature button. The car can be driven in this mode to get ongoing temp readings.
80 C is 176 F
85 C is 185 F
90 C is 194 F
95 C is 203 F
100 C is 212 F
105 C is 221 F
110 C is 230 F
115 C is 239 F
120 C is 248 F
125 C is 257 F
130 C is 266 F

Since the issue, if I read this correctly, is only under load I would suspect the radiator first. Also check the spark plugs to see if there is any sign of a head gasket issue (while unlikely) just to be certain.
H

[Ccmano]

If you haven’t already done so, read up on the cooling system and it’s issues. Dynomite provides an excellent review in the “Solutions” sticky at the top of this Technical section.
H

http://forums.corvetteforum.com/c4-z...post1580070558

[lfalzarano]

So it only overheats when the nose of the car is pointing “up hill” and not in any other direction? I assume that when driving up hill, the revs are a lot higher than when driving down hill or on level ground. If that is the case, it could be the water pump internal blade is going bad. Just a hunch... & JMHO


Lou

[efnfast]

What does orange coolant do to the system?

[DRM500RUBYZR-1]

Follow the instructions in post # 4, and replicate the driving situation and observe the temperature on the HVAC display.
This will confirm the actual temperature far, far better than the gauge.
The gauge is non linear, and is known to be highly inaccurate at times.


While it does sound as if you have a problem, let's be certain first that there is.


Next look for and clear the debris as described also above. Hoover wishes their vacuums worked half as well as the C-4 cooling air intake that indeed sucks up everything, including soda cans!


Next, while monitoring the true temperature on the HVAC, start and watch the fan behavior.


Fan 1 should come on exactly at 228. When it does, you should see an immediate decrease in the rate of temperature rise.
If it succeeds in keeping you at or below 228, you will not see the 2nd fan activate, as it comes on at 240 I believe.


If all of that goes as it should turn on the AC which should bring on both fans immediately regardless of temperature.


If all of that checks out, take a careful look and feel of the lower radiator hose, to ensure that it is not collapsing under load.


If OK, it's then onto the water pump function and radiator function.


The fact that it is not pushing coolant into the overflow tank causes me to want to make sure it is really overheating before going any further.


7/8 on the gauge would likely eject coolant when shut down, but as mentioned 7/8 on that gauge may mean nothing, so start simple first.


You will find and correct it!
Marty

[ChattanoogaJSB]

Wow! So many welcoming and helpful replies. Let me try and address a few comments.

1) yes I’ve read most of the forum stickies on this topic but at different times; I will revisit

2) the orange coolant seems to gum up more than the green, we are trying to find out if we have a photo from our inspection that shows it. I do not but my friend might. That’s all academic now but it might point toward being gummed up.

3) I do tend to believe it’s an obstructed radiator, I’ll have to find out what I can leave in place on removal. Hopefully the ac condenser and oil cooler can stay plumbed.

4) my friend drove it today. In just ten minutes of hilly driving (not up the mountain) it peaked at 110 C / 230 F with one fan on. Ac brings on both fans. He did the temp display procedure.

5) I will double check the plugs for any visible “steam cleaning”

6) I still owe you guys photos!

7) anything I missed replying to I will address after dinner and my thanks again!

Benton

[ChattanoogaJSB]

Analog vs digital at 230 degrees actual

Similar to what my IR gun shows on engine