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Old 07-07-2018, 12:13 AM
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unforgivener
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Hey guys. It's been in the upper 90's here in Albuquerque, NM lately and my '89 coupe isn't liking it very well. The highest she would go up to just before summer was 230 degrees. Now in the mid 90's with the ac on, she wants to go over 240 degrees! When it does hit 240 degrees, I turn ac off and roll windows down. Soon it will drop to low 220's.
So, I finally got the ac working, I actually have the secondary fan hooked up to a manual switch. But it still climbs to 240 degrees with both fans running.
i am running a 160 temp thermostat, along with 50/50 coolant. I have even tried straight water just to see if it would run cooler...nope!
Radiator is not plugged with debris, but could the single row radiator be the culprit? Any ideas where to shop for a bigger radiator? Unless u think i'm overlooking something

Thx, Pat

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Old 07-07-2018, 02:23 AM
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overheat while driving or when stopped at a light or both?
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Old 07-07-2018, 07:36 AM
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That is what my 1986 would do all stock, with the air on and 90 degrees it would overheat, 240 plus. I switched radiators to a DeWitt and problem solved. There may be cheaper options out there.
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Old 07-07-2018, 03:25 PM
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93 up here yesterday and i wanted to test this exact thing on my base 86 that recently had the following done to it:

new elecric rad cooling fan motor

prestone flush where chemical stayed in for 5 months

fins straghtened on both rad and condensor, grit and dust washed out of both

kc4 oil cooler installed

installed fromt air dam.

engine resealed using hylomar + permatex aviation form a gasket where applicable

fresh 50/50 coolant

up until this point i couldnt get my temps in line and then....

discovered BLOCKED CATALYTIC CONVERTOR and REMOVED

.....results from hhhaarrddd driving in 93--97f yesterday were, max oil 109c max coolant 109c !!


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Old 07-07-2018, 03:58 PM
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Is the lower air dam in place with no tears or broken off chunks? The air dam is what directs air up into the A/C condenser and radiator. Are the fins around the radiator tubes or the A/C condenser crushed to where air flow is reduced?

Have you done a cooling system flush? To do that properly, you need to remove the knock sensor(s) from the block. That will get the balance of the coolant out of the block. It's common for sludge to build up in the block passages and that keeps coolant from circulating. Removing the knock sensors will even give you a chance to use a thin rod to scrape out any sludge allowing coolant to flow out.

Are the upper and lower hoses in good shape? It may be that a hose is collapsing and cutting down the flow of coolant IMHO, a 160 degree 'stat doesn't really help. It simply allows the coolant to circulate earlier compared to a 180 or 195 'stat. If the radiator is original to the car, it may simply be ready for a new one. Or take it to a shop that can clean out the tubes.
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Old 07-07-2018, 06:48 PM
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Originally Posted by unforgivener View Post
Hey guys. It's been in the upper 90's here in Albuquerque, NM lately and my '89 coupe isn't liking it very well. The highest she would go up to just before summer was 230 degrees. Now in the mid 90's with the ac on, she wants to go over 240 degrees! When it does hit 240 degrees, I turn ac off and roll windows down. Soon it will drop to low 220's.
So, I finally got the ac working, I actually have the secondary fan hooked up to a manual switch. But it still climbs to 240 degrees with both fans running.
i am running a 160 temp thermostat, along with 50/50 coolant. I have even tried straight water just to see if it would run cooler...nope!
Radiator is not plugged with debris, but could the single row radiator be the culprit? Any ideas where to shop for a bigger radiator? Unless u think i'm overlooking something

Thx, Pat
When is the last time you had the radiator out and cleaned? All the fans in the world won't help if there is no flow



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Old 07-08-2018, 04:47 PM
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I know most of us check the debris between the radiator and the condenser but that is not good enough. You really need to go the distance and clean it better so I have been doing this for several years now. I built a thin right angle air gun so I can reach the bottom of the radiator and condenser and all 4 surfaces. I first blow out toward the front of the car (and then rear) and then go back and forth till I can't see anything else coming out. This can take a good while. You can't believe the crap that comes out the first time.

You have to raise the shroud and remove several hoses and the top A/T line has to be disconnected. I just have a bungee cord to hold one end up as you don’t need to completely remove it. I also replace the coolant, flush the radiator and clean out the heater core with a hose (gently). I do the heater last so I can re-connect the A/T line and drive it out of the garage (where I do the blowing out first) and where I can use the garden hose and make a mess.

I threw this together quickly one day as I thought I'd never use it again but now part of my special tools. Just made it of a mop stick, duck tape, rubber and plastic hoses. It works real well.

This process will give you an additional edge on better cooling but only closer to factory specs. I know a bigger radiator is really required for us guys who live in 90-100 heat most of the year. I think the corvette engineers and designers all lived up north.








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Old 07-08-2018, 06:49 PM
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Here is what I found after my (since sold) 89 pegged 240 in bumper to bumper traffic. In fact the AC blow off valve engage. WTF?

Once I cleaned it out I would never go over 215 with the AC on in 105 Texas heat. Air flow is everything.
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Old 07-10-2018, 01:17 AM
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Originally Posted by unforgivener View Post
could the single row radiator be the culprit? Any ideas where to shop for a bigger radiator?
1. No. The stock radiator should be better than good enough. GM tested your car in temps WAY hotter than you're seeing, and proved that it wouldn't over heat. You need to do some cooling system maintenance.
2. DeWtitts....but see "1.", first.
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Old 07-10-2018, 02:16 AM
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Originally Posted by VikingTrad3r View Post
overheat while driving or when stopped at a light or both?
It's actually doing both. When stopped it climbs rather quickly. Start driving and it drops but will start climbing again...
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Old 07-10-2018, 02:18 AM
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Originally Posted by bjankuski View Post
That is what my 1986 would do all stock, with the air on and 90 degrees it would overheat, 240 plus. I switched radiators to a DeWitt and problem solved. There may be cheaper options out there.
What did the rad set you back, and how hard was the labor?
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Old 07-10-2018, 02:24 AM
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Originally Posted by VikingTrad3r View Post
93 up here yesterday and i wanted to test this exact thing on my base 86 that recently had the following done to it:

new elecric rad cooling fan motor

prestone flush where chemical stayed in for 5 months

fins straghtened on both rad and condensor, grit and dust washed out of both

kc4 oil cooler installed

installed fromt air dam.

engine resealed using hylomar + permatex aviation form a gasket where applicable

fresh 50/50 coolant

up until this point i couldnt get my temps in line and then....

discovered BLOCKED CATALYTIC CONVERTOR and REMOVED

.....results from hhhaarrddd driving in 93--97f yesterday were, max oil 109c max coolant 109c !!

Wow...was your performance being affected at all? Any error codes being generated? So you removed the converter...did you install a new one?
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Old 07-10-2018, 02:35 AM
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Originally Posted by c4cruiser View Post
Is the lower air dam in place with no tears or broken off chunks? The air dam is what directs air up into the A/C condenser and radiator. Are the fins around the radiator tubes or the A/C condenser crushed to where air flow is reduced?

Have you done a cooling system flush? To do that properly, you need to remove the knock sensor(s) from the block. That will get the balance of the coolant out of the block. It's common for sludge to build up in the block passages and that keeps coolant from circulating. Removing the knock sensors will even give you a chance to use a thin rod to scrape out any sludge allowing coolant to flow out.

Are the upper and lower hoses in good shape? It may be that a hose is collapsing and cutting down the flow of coolant IMHO, a 160 degree 'stat doesn't really help. It simply allows the coolant to circulate earlier compared to a 180 or 195 'stat. If the radiator is original to the car, it may simply be ready for a new one. Or take it to a shop that can clean out the tubes.
Upper and lower hoses new. Air dam is in good condition. I haven't tried the flush. I have heard the 160 won't help with over heating, just opens up sooner. Really considering a new radiator...
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Old 07-10-2018, 02:37 AM
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Originally Posted by Cruisinfanatic View Post
When is the last time you had the radiator out and cleaned? All the fans in the world won't help if there is no flow
Never. Is it alot of labor?
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Old 07-10-2018, 02:45 AM
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Originally Posted by pcolt94 View Post
I know most of us check the debris between the radiator and the condenser but that is not good enough. You really need to go the distance and clean it better so I have been doing this for several years now. I built a thin right angle air gun so I can reach the bottom of the radiator and condenser and all 4 surfaces. I first blow out toward the front of the car (and then rear) and then go back and forth till I can't see anything else coming out. This can take a good while. You can't believe the crap that comes out the first time.

You have to raise the shroud and remove several hoses and the top A/T line has to be disconnected. I just have a bungee cord to hold one end up as you donít need to completely remove it. I also replace the coolant, flush the radiator and clean out the heater core with a hose (gently). I do the heater last so I can re-connect the A/T line and drive it out of the garage (where I do the blowing out first) and where I can use the garden hose and make a mess.

I threw this together quickly one day as I thought I'd never use it again but now part of my special tools. Just made it of a mop stick, duck tape, rubber and plastic hoses. It works real well.

This process will give you an additional edge on better cooling but only closer to factory specs. I know a bigger radiator is really required for us guys who live in 90-100 heat most of the year. I think the corvette engineers and designers all lived up north.







That's an awesome tool! I don't have an air compressor, so I will at least pull the shroud and do what I can to clean her out!
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Old 07-10-2018, 02:49 AM
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Originally Posted by billschroeder5842 View Post
Here is what I found after my (since sold) 89 pegged 240 in bumper to bumper traffic. In fact the AC blow off valve engage. WTF?

Once I cleaned it out I would never go over 215 with the AC on in 105 Texas heat. Air flow is everything.
That pic sure gives a good example, huh? Definetly gonna look into this and a flush!
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Old 07-10-2018, 02:52 AM
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Originally Posted by Tom400CFI View Post
1. No. The stock radiator should be better than good enough. GM tested your car in temps WAY hotter than you're seeing, and proved that it wouldn't over heat. You need to do some cooling system maintenance.
2. DeWtitts....but see "1.", first.
Yah, I hear ya loud n clear. I'm in need of some maintenance for sure. Gonna tear into it asap. Will post my findings
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Old 07-10-2018, 06:47 PM
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Originally Posted by unforgivener View Post
Never. Is it alot of labor?
a couple hrs
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Old 07-10-2018, 06:52 PM
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And stock fans temperatures are usually above 220 for them to turn on. For c4's with 2 fans, turning ac forces both on.
But, cleaning may be in order ..
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Old 07-10-2018, 09:02 PM
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Originally Posted by unforgivener View Post
Could the single row radiator be the culprit?
Yes! It could be and it most likely is. The cooling systems on C4-C7 Corvette is not like previous years where the radiator was robust and had extra capacity to deal with things like 100 degree days and stop and go traffic. In the old days the thermostat could modulate and maintain the temperature at a given level. The newer cars, with thin aluminum radiators are no longer controlled by the thermostat. The temperature is now controlled by the radiators capacity and the ambient air temperature. When the radiator is new and clean (inside and out) the system works fine but when crap builds up or outside temperatures get really high, there is no extra capacity to compensate. Now I do not want to start the whole thermostat debate, been there-done that, but if a given radiator and fan system had the ability to lower your coolant to the stat setting it would. In fact, it would try to go lower than the stat and that's when it would modulate and control things. This doesn't happen anymore. The temperature blasts past the stat setting, the stat goes full open and it's basically useless at that point. It is because of this I think all C4's need the radiator upgraded. I mean when it's really hot out I want the AC on, not the heater.

DeWitt offers both double row and single row upgrades. Often members complain about the cost of the double row although they are competitive with the other major US made brands. The double row 1.0" tube radiator is a 100% increase in cooling capacity. That's like putting two radiators in your car and it works really well but you may not need all that.

DeWitts single row 1.5" cores are a 50% bump in capacity and they do a great job at an affordable ($380) price.

1984-89 Corvettes use part # 1129084A (all)

1990-96 Corvette Use part # 1129090A (automatic) or 1129090M ($ 349.99 manual)






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