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Old 05-15-2018, 05:16 PM   #1  
PaulZR1
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Default overheating

While highway driving the car seems to stay fine at 180, upon exiting into stop and go traffic, the car then starts to get hot to the redline at 260. What can I do to get the car to keep cool in the proper operating temperature ?
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Old 05-15-2018, 05:32 PM   #2  
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First place I would start is to verify fans work. An easy way I've found to check is to crank car & turn on air conditioning. With hood opened, carefully verify fans spin. We can go from there.

Ted
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Old 05-15-2018, 07:50 PM   #3  
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Make sure you have good air flow. The area in between the radiator and condenser is notorious for collecting debris. You will need to inspect, then pop off the shroud before you vacuum, water flush and dig out leaves, bugs papers bags or cigarette butts.

If you have an debris issue, the cleaning will make a huge difference

Here is what I found "in the in between"
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Old 05-16-2018, 11:38 AM   #4  
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Could also be a partially stuck thermostat.
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Old 05-16-2018, 12:38 PM   #5  
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Well, in ANY CASE, you don't ever want to let the all aluminum LT5 get close to 260.

According to Marc Haibeck, the difference in the greater expansion rate of aluminum with temp vs. the steel head bolts results in the head gasket getting crushed - namely the metal compression seal ring around the cylinder. Once the heat is reduced, the aluminum retracts, but the gasket will not rebound and a coolant leak will develop.

Replacing a head gasket means the engine has to come out because re-timing the cams can't be done practically with the engine in the car.

too that the radiator eventually gets full of dirt and grass clippings (discharged by lawnmower to the side of the road). I replaced my broken rad with a stock one that Pete removed from a car someone was having him install a new 4-row radiator into.

Before installing the used rad, I flushed it (or course), but boy what a surprise I got when I pressure washed the cooling fins. There musta been a quart of mud and sand that was forced out of that core! No wonder someone thought they needed a new radiator.
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Old 05-16-2018, 02:28 PM   #6  
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Thank you all so much for your quick replies. I've already replaced the old thermostat with a new one (this past Tues). I'll try the pressure washing. Thanks again guys.
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Old 05-16-2018, 07:58 PM   #7  
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Quote:
Originally Posted by PaulZR1 View Post
Thank you all so much for your quick replies. I've already replaced the old thermostat with a new one (this past Tues). I'll try the pressure washing. Thanks again guys.

Just to remind you, what Paul said, "pressure washed before installing."

You cannot effectively pressure wash or blow compressed air through the radiator while it is installed. You must remove it to do the job.
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Old 05-19-2018, 11:35 AM   #8  
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Quote:
Originally Posted by A26B View Post
Just to remind you, what Paul said, "pressure washed before installing."

You cannot effectively pressure wash or blow compressed air through the radiator while it is installed. You must remove it to do the job.
Jerry is correct--you need to remove it to clean it. In my '93 I had overheating problems. Took it to my local ZR-1 dealer mechanic at the time, had the radiator removed and it was roughly 40% blocked with debris. Once it was hosed out it ran fine for as long as I owned it. Back in the late '90s when I had it done it cost about $300 to have it done. Afterward I installed a 1/4" mesh screen over the bottom feeder air intake opening to prevent further leaf pickup in the fall. A good modification todo. BTW, I would be careful using a pressure washer on a radiator--they are powerful and can damage the fins. I would use a regular hose perhaps with a nozzle to get all the water in you will need. --Bob

Last edited by ZR1Bob; 05-19-2018 at 11:38 AM.
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Old 05-19-2018, 11:51 AM   #9  
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After you clean everything and flush system well, If you decide you neede a 160* thermostat let me know, I make them upon request.
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Old 05-19-2018, 03:43 PM   #10  
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Did the oP ever confirm his actual coolant temps w/the digital display? Or did he see the "idiot light" analog gauge heading toward 260 and panic?




Quote:
Originally Posted by Dynomite View Post
Keep the RPM above 2,000 rpm at all stops.
No way this is necessary. Not on a properly running car. No way.
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Old 05-20-2018, 12:03 AM   #11  
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Originally Posted by Dynomite View Post
OK.......but if outside air temperature is 100 deg F or higher ???
And you are sitting letting the LT5 run at 750 rpm......for a few minutes......
Yeah? So?

GM didn't design the car so you'd have to sit and hold the throttle at stops. That's ridiculous. The ZR-1 had to go through the same validation as all the other GM products...that means testing in Death Valley, Davis Dam and other places where the temp soars above 100˚F. Car should be able to sit idling all day long in 100+ temps. If it can't there is something that needs attention; cleaning, flushing, fans...whatever.

But in this OP's case, I think the first priority is to determine how he came up with "the car then starts to get hot to the redline at 260". B/c if he's looking at the analog gauge, he very likely has no issue at all.
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Old 05-20-2018, 12:10 AM   #12  
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Yup, gotta go off the digital coolant reading
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Old 05-20-2018, 09:26 AM   #13  
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One of the best things you can do is get a custom prom. I never see temps over 205 even in heavy traffic on a hot day.


This for the 91 you did not list your year but the links are on Marc's site

http://zr1specialist.com/HAT%20Web/p...on%20BFXBG.htm
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Old 05-20-2018, 11:18 PM   #14  
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Quote:
Originally Posted by PaulZR1 View Post
While highway driving the car seems to stay fine at 180, upon exiting into stop and go traffic, the car then starts to get hot to the redline at 260. What can I do to get the car to keep cool in the proper operating temperature ?
What was the ambient temperature?
What thermostat did you install (180 deg Stant?)

See Post 9 - HVAC Temperature Display And Radiator Efficiency Test Runs

Quote:
Originally Posted by Tom400CFI View Post
So?

Car should be able to sit idling all day long in 100+ temps. Need more information on that suggestion (Details as to what car for example?). I am trying to figure out what I am doing wrong
I deleted my other posts so we can start at square 1

So....Do it (idle the LT5 in ambient 100+ deg F and report back)
Tell us what Thermostat you are using (actually once thermostat is fully open makes no difference what deg thermostat you are using), Ambient Temperature, Idle Time, Idle RPM, and Coolant Temperature in Deg C (using Digital HVAC Display), and if you are using a multi-core aluminum radiator. (remembering the LT5 water pump operates over a very broad range of engine RPMs which is NOT and easy design function). Also tell us if you are using an original thermostat as they do change somewhat over time.

And....if you are using Fans On 205 deg F and Fans Off 200 deg F with Marc Haibeck Chip.
Some say battery voltage (alternator) plays a part as lower voltage effects fan speed.

Last edited by Dynomite; 05-21-2018 at 10:39 PM.
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Old 05-20-2018, 11:50 PM   #15  
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Quote:
Originally Posted by Dynomite View Post
What was the ambient temperature?
What thermostat did you install (180 deg Stant?)

See Post 9 - HVAC Temperature Display And Radiator Efficiency Test Runs



So....Do it (idle the LT5 in 100+ deg F and report back)
Tell us what Thermostat you are using (actually once thermostat is fully open makes no difference what deg thermostat you are using), Ambient Temperature, Idle Time, Idle RPM, and Coolant Temperature in Deg C (using Digital HVAC Display), and if you are using a multi-core aluminum radiator. (remembering the LT5 water pump operates over a very broad range of engine RPMs which is NOT and easy design function). Also tell us if you are using an original thermostat as they do change somewhat over time.

And....if you are using Fans On 205 deg F and Fans Off 200 deg F with Marc Haibeck Chip.
I'd love to run that test....People who know me on these forums know that I like to seek fact and I'll test things. I do it all the time. However, I have an LT1. Stock stat, stock fan settings. It has a Tom DeWitts radiator b/c the side tank cracked in the stock one...but it would behave the same with either radiator. It'll idle all day long in 104˚F temps. Of course, temps will run up to 230˚F -the "fan on" temp...but then it cools right down to 217˚F -the "fan off" temp. It'll do that all day. If I run the AC (fans forced on), it won't go above ~200˚F. Why should or would the LT5 generate significantly more heat than my LT1, at idle?

How did the ZR-1 get validated if, during testing, part of SOP was to "rev it to 2000 RPM at stop lights"? Doesn't make any sense. I really don't think GM would produce a car that has that kind of requirement. The LS7 has the same RPM range as the LT5...I don't believe you have to hold it at 2000 RPM at stop lights, or that it's cheap-o stamped steel water pump impeller has any issues running from idle to 7000 RPM. Does it?


EDIT: I see people complain about "overheating" constantly on these forums. It always ends up being a maintenance issue or the worthless analog gauge issue -which I'm still betting is the OP's issue. Anyway, the stock cooling system on any GM product should be way better than "good enough" for the vast majority of temps that we're going to encounter. Last summer, I "Dual drove" my LT1 in an auto-x with my wife on a 100K+ day. My car is well maintained (I'm sure yours is too, based on your posts and pics) and it's temps never went above 215 (AC on); idling, racing, whatever. It was in use, non-stop for each heat. Better than good enough.



.

Last edited by Tom400CFI; 05-20-2018 at 11:57 PM.
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Old 05-21-2018, 07:26 AM   #16  
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Quote:
Originally Posted by Dynomite View Post

And....if you are using Fans On 205 deg F and Fans Off 200 deg F with Marc Haibeck Chip.
Some say battery voltage (alternator) plays a part as lower voltage effects fan speed.
Little more information on this please. My voltage only drops for a split second when both fans cut on and even than no less than 13.4

Run this set-up on both my 91 & 93, It is my understanding both fans come on together cool down time to 200 is less than a minuet.
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Old 05-22-2018, 05:29 AM   #17  
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Quote:
Originally Posted by billschroeder5842 View Post
Make sure you have good air flow. The area in between the radiator and condenser is notorious for collecting debris. You will need to inspect, then pop off the shroud before you vacuum, water flush and dig out leaves, bugs papers bags or cigarette butts.

If you have an debris issue, the cleaning will make a huge difference

Here is what I found "in the in between"


A radiator cap on an LT5 Radiator?????

Quote:
Originally Posted by FASTAZU View Post
Little more information on this please. My voltage only drops for a split second when both fans cut on and even than no less than 13.4

Run this set-up on both my 91 & 93, It is my understanding both fans come on together cool down time to 200 is less than a minuet.
So you have Haibeck chips?
I would not focus on voltage as I assumed that was extreme cases where the ZR-1 battery was failing and not taking a charge.

The key is ambient temperature as an ambient temperature of say less than 90 deg F does not cause the same issues when in stop and go traffic.

When you say coolant reached 200 deg F in less than a minute.....what was the ambient temperature and what was the engine rpm?

Last edited by Dynomite; 05-22-2018 at 05:36 AM.
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Old 05-22-2018, 06:42 AM   #18  
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Quote:
Originally Posted by Dynomite View Post

So you have Haibeck chips?
I would not focus on voltage as I assumed that was extreme cases where the ZR-1 battery was failing and not taking a charge.

The key is ambient temperature as an ambient temperature of say less than 90 deg F does not cause the same issues when in stop and go traffic.

When you say coolant reached 200 deg F in less than a minute.....what was the ambient temperature and what was the engine rpm?
Yes both Haibeck chips, 60 sec. or less from 205 to 200 85-95+ summer temps at idle 750-800. takes another 60 to 180 to climb back to 205 again at idle 85-95+ summer temp. Once you start moving 25+ mph they don't cycle on temps stay around 202+ or- a few.
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Old 05-22-2018, 07:31 AM   #19  
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Quote:
Originally Posted by Dynomite View Post

A radiator cap on an LT5 Radiator?????
Ha!- Great "eagle eye!"

This was my 89 that I cleaned out after I bought it last year. It made all the difference in the world after I un clogged the air flow. I included it to show how messed up the C4 radiators can get with almost no effort.

I did swap radiators on my LT5 about 18 months ago with a stock replacement after a small leak. I alos took the opportunity to put in a fresh set of Jerry's silicon hoses. The water pump was a royal PITA.
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