My car has typically run around 220*, with the fans coming on at 228, which I had been told was normal. Today while driving, I noticed that the temp got up to 229 & as high as 233. Normally as soon as it hits 228 the fans would come on and cool the engine to around 215. I noticed that if I turned off the a/c the temp would go down as normal to around 215. What on the a/c would cause this?

 

The condensor.

The a/c condensor runs every bit as hot as the engine.

Your a/c does NOT provide cold air. It removes HOT air in a heat exchange process and the heat is delivered to the atmosphere thru the condensor. When there is a great deal of heat there it tends to pre-heat any fresh air that goes to the radiator so there is less of a temp differential there for engine cooling.
You have a couple options if this becomes a problem...
increase air flow thru the condensor somehow, by modifying the air-dam, or adding a pusher fan, or by running the main sucker fan(s) more so there is always some airflow thru the condensor and radiator. Airflow is the key. If there is adequate airflow to both things up front you will never see high temps on the gauge...but if there is little or no flow, what IS there gets spuerheated and causes a cascade effect and gets everything else hot.

Coolant/ antifreeze makes the engine run a few degrees hotter also. Plain water cools best but thats bad for the metals. The thicker the coolant the more it collects and holds heat. The antifreeze is designed to raise the boiling point, not increase the cooling efficiency.
try adding water-wetter to the radiator and make sure the mix of water/anti-freeze is no more than necessary.

 

Here's what I've done: drained coolant from engine & flushed it. The guy at the parts store recommended I try the Prestone Dex-Cool coolant for GM, so I got the 50/50 mix and put it in. I drove around today and the highest temp I got was 227 when I drove it hard. Under normal driving it stayed between 217 & 225. Also I did forget that I removed the front air dam when I was doing some work and never got it put back on. I plan to get it back installed and hopefully this will lower the temps more. One thing to remember, today while I was driving the weather was not as hot as yesterday when I saw the problem. I live in Florida where it gets pretty hot, I hope there is no issue later in the summer.

 

I believe Dex Cool is the Red stuff and was only used in 1996 Corvettes. I hope your car is a '96 so you don't have any problems. I'm pretty sure all other years of C4's use the Green stuff....

 

Yes, it's the red stuff. My L98 engine is an 87. What kind of problems could this cause? I'm going to do some research and get back with you.

 

Don't mix the stuff. If the car required the green then use that.

If the temps don't come down fast enough then you have to change the rad and/or change the water pump. If those don't work the way they are designed then you can add all the fans you want and the efficiency just won't be there.

Anti-freeze is just that...it prevents freezing. It also is a corrosion inhibitor. Use what the engine was designed for.

I used to have high temps and the fans on all the time in my 1986. When I changed the water pump and put a new rad in the pusher fan comes on occassionally in hot weather and the main fan hasn't come on in a long time. An efficient rad helped.

My 2 cents.

 

Is the secondary cooling fan (in front of the radiator) coming on when you turn on the AC?

If not, then you may either have a bad relay or a bad switch.

 

My car has 2 fans, a primary and a secondary. The secondary (Big fan behind the radiator) goes on with the A/C, so when the car gets hot and you put on the A/C the large fan will go on and actually cool the car down. I have a wire schematic that shows you how to wire both fans to come on from the driver-side temp switch without bypassing the relay, I just haven't had the time to do it, I think it's a good idea. I have a 180 stat with a 195 switch, the car is meant to run within a certain temp range for optimum performance. Having that shroud off is causing more heat for sure. Go to corvettecentral.com and go to C4 articles and look for the wire diagram for fan operation, maybe you'll get it done and tell us how you did it I've been lazy. Another thing you might want to do is make a front air dam, which I'm finishing off today.

 

Definitely replace the air dam. The center section is what helps to direct air toward the A/C condenser and radiator.

You can use Dexcool in the engine (Dex was the factory fill starting in '95) but you need to make sure that you have completely flushed out the old green coolant. The two coolants do not mix and will create a brown sludge that will block cooling passages. I would drain the system and then fill with water only, start the engine and bring it to operating temp. Shut down, drain again, refill with water, run and drain. Do this three times, then you can fill with Dex and distilled water.

It also sounds like you have some dirt and debris clogging up the passages between the fins and tubes in either the A/C condenser and/or the radiator. This keeps air from flowing through and the radiator cannot cool the fluid down. Does the car have the additional cooling fan in front of the A/C condenser?

Another possibility is that the lower radiator hose is collapsing and that reduces the amount of coolant flow. How old are the hoses?

If the radiator is the original one, it may be time for a replacement. The tubes in the radiator will eventually become very thin due to years of coolant flow and that reduces the ability of the radiator to provide adequate heat transfer, resulting in a loss of cooling ability.

 

The liquid it's making in the Condenser is about 100 degrees so no, it's not the same temp as the Coolant. In fact, to keep that liquid at around 100, the fans come on sooner and stay on longer meaning that your coolant temps will be 10 to 20 degrees less than when it's off. When it doesn't work that way, it's one of three things: 1. The temp gage is inaccurate. Scan to see what the Coolant Temp Sensor shows. It should be about the same as the Display. 2. Air flow is blocked and when it can't get rid of the heat, it overheats so make sure there isn't a bunch of debris between the Condenser and the Radiator. 3. The a/c system is plugged up creating too much pressure (temperature rises in proportion to pressure). Hookup a manifold gage set and see what the high side is showing or go to a shop and have them check it out. As a guideline, it should be anywhere from 200 to 250 psi with the fan cranking and the engine at 1200 to 1500 rpms, Air Temp at the Condenser 70 to 90 degrees. Anything above that indicates there's a problem - more than likely junk in the metering device or orifice from compressor wear or an Accumulator that's crumbling away (and that's usually from a gas conversion done wrong).

 

Yes, the secondary is coming on.

 

Before I used the Dexcool, I did just as you said, flush the system with water, however I did it only two times, and then I just let water flow through with the pressure from the water hose.
I had already checked the radiator hoses, the seem fine, the lower hose has the spring inside to keep it from collapsing.

 

Ok, today I'm draining out the Dexcool, too much negative feedback on it. I'm draining the system and running a flush. I will be going back with the regular green coolant. I'll let you know how it comes out after I've finished and had time to drive it.

 

the 50/50 mix from prestone is compatible with the red dex-cool and green prestone. I am using this in my 95 but if you look at the dexcool properties and the green it is the same formula. I think the 50 /50 mix is a dexcool clone which I did read it here on the forum. The old fashion green prestone is very hard to find

 

have you ever taken the radiator out and cleaned it?
This is what they can look like

 

Actually, I took the radiator out and cleaned it before I ran the flush. There were some leaves and trash in between the condenser and radiator but nothing like the picture. I also found that my primary fan worked intermittently, so it did not run every time it was suppose to. I replaced the switch in the side of the head, however while replacing the thermostat, I cracked the water outlet, now I've got to get a new one, so I don't know if anything I've done is going to work yet. My local stor has a replacement but they have already closed for Easter. Will pick it up tomorrow.

Other question; At what temperature should the primary fan come on and off?

 

I got my water outlet replaced and the engine is back running. All the work made a good improvement, the engine ran cooler, between 215 & 227. It averaged at around 220 most of the time. Here is what all I did: drained system, removed radiator and cleaned all debri between radiator & condenser. I ran water through radiator while I had it out just to flush it. I also cleaned the cooling fins on the radiator & condenser coil. I reinstalled the radiator, ran a system flush, then drained it. I filled it up with water and flushed it three times with just water. Drained system, installed 160* thermostat and added 50/50 mix green coolant.