My car has the fans programmed to turn on earlier, a dewitt radiator, and a 160 degree thermostat. The engine was staying very cool in the fall, winter, and spring. Now with outdoor temps reaching the 90's I saw it get to 240 this weekend. It only gets hot with the AC on and in traffic. If the AC was turned off I'm sure it would have stayed around 180-190 as usually. Going about 70mph the temp is usually about 177-180. It has fresh coolant, head gaskets, radiator, no debri or rocks, and the trans cooler is external in front of the condensor not in the radiator. I realize air passes through the condensor before hitting the radiator which is contributing to it getting hot. But 240 seems a little too hot. I have a Mezierre HD EWP which is not yet installed but should solve the problem. Unless it is strictly an airflow issue which is probably the case. Any ideas on why the AC is causing it to climb so much? I have never had the AC system serviced. Whould that help?

Thanks

 

Well the A/C puts a load on the engine and then you are not moving, so there is more heat. A better fan would help perhaps?

 

I agree with the air flow diagnosis. I think if your A/c isn't working properly, it would be putting less, and not more, heat into the air to the radiator. How long has the radiator been in there? You pretty much have to remove the radiator to check for and remove the debris between the condensor and the radiator. Because it is a custom installation, no idea what you have to do to check between the aux cooler and the condensor.

RACE ON!!!

 

Make sure that both fans are coming on. I had one of mine to go out and it would overheat on hot days but 1 was enough on cooler days.
Also, has anyone put freon in the system lately? A overcharged system will in turn cause the motor to run hot. Its the overcharge drives up the condenser tempature and then that air goes through the radiator.

 

Took the words right out of my mouth. Its possible only 1 fan is working also.

 

i live in FL and it does get REALLY hot here....well iv had my AC on latetly an...iv actually noticed my temp. stays around 190ish...and i do also have a 160thermostat...an it stays 190ish when its in park with the car on with the AC running....soo i dont know lol

 

Thanks for all the replies so far. I installed the Dewitt about 4 months ago. At that time I also completely flushed the system. The condensor and aux cooler were not blocked. The freon has not been changed and the AC has not been serviced since I bought the car in 2004. The AC does blow cold though. I'll keep an eye on the fans this week to see if they are both turning on. They were both working at the time I installed the new radiator. Any recomendations on direct fit replacement fans if needed? Perhapse something with a higher flow?

 

I have a 94 and it was getting too hot for me. I did as you did, except for the Dewitt part. Your car should not get that hot with the modifications you've done. Even just the thermostat and the fan reprogram should have done it. I suspect your water pump is not working properly. Have you considered modifying it with an electric pump? It's an easy mod to do and I bet it would fix your issues here. Do your fans run properly? If the water pump is working then your fans might need attention.

Just my 2 cents....

Billy

 

my stroker motor with a stock radiator, 160* thermostat and reprogrammed fans stays 180-190 in 96* humid florida heat with the AC at full blast..

It sounds like one of your fans is not working (verify), A/C over or under charged (have it checked and serviced), bad radiator cap, low coolant level, ait bubble in system (dont forget to purge the system - screw is on top of the thermostat housing), incorrect timing (chain jumped - how is it running??) or a head gasket..

oh, BTW whats the condition of your fan shroud? also how is the spoiler under the car?

good luck!

 

I too have a NEW OEM radiator and my entire cooling system is stock except for a 160 degree thermostat and the fans programmed earlier.

My car has minor mods (heads and cam).

Since I believe the weak link in the C4 cooling system is the airflow at idle, I made foam rubber strips to seal the perimeter of the radiator to the inside of the fan shroud. This forces all air to go through the radiator.
Using aluminum sheet metal, I made panels to seal the holes in the entire fan shroud -- particularly where the A/C lines enter the fan shroud. This keeps hot under-hood air from being drawn into the front of the radiator when the fans are running.
And, I bought a second power steering cooler and mounted in front of the existing power steering cooler for my auxillary ATF cooler. I bent hard lines to go from the in-radiator ATF cooler return line through my aux cooler and back to the transmission.
For other cars, I have put the aux ATF cooler in front of the radiator -- but for a C4 with the very poor airflow, I simply won't do it because it limits the already scarce air supply even more.
All these mods keep my engine at 185* on 95+ Florida days while in traffic and the A/C going with an OEM radiator. I couldn't be happier.

When moving at speed, the air movement creates a positive pressure in front of the radiator and this forces the air *out* the A/C condenser line hole in the fan shroud.
But, with the fans on in traffic, there is negative pressure in front of the radiator and it pulls hot under-hood air into the front of the radiator.
That is why I seal the holes.

Tom Piper

 

When I flick my A/C on, the temp drops by almost 30 degrees.

 

The humidity in the "humid florida heat" has zero effect on your car's cooling system.


A bad radiator cap will prevent the coolant from getting that hot. It will boil out long before it hits 240° in a non pressurized system.


These items are important, but not likely to a problem only at low speed.


Good points. It IS an air flow problem.

Mr Mojo's temps drop 30° when he flicks on the A/C because that also gets his fan(s) running...Air flow.

RACE ON!!!

 

If the a/c system is plugged up that increases pressure at the condensor. Pressure is heat with most systems designed to maintain an average condensor temp of no more than 120 to 150 degrees or about 200 to 220 psi. That's why the condensor is in front, and because pressure/temp builds a trillion times faster than coolant temps, the fans come on sooner and stay on longer. Anyway, if it's heating up with the a/c on, check pressures. If the high side is greater than 2.2 times the temp of the air at the Condensor, it's either time to suck it all out and clean the metal that's lodged in the Orifice, or you've tried to cram 10 lbs of potatoes into a 5 lb sack. When it's right, you should be shedding 5 to 10 degrees on the coolant temps at idle - maintaining the thermostat at cruise.

 

I see your logic.

However, it seems to me that the A/C wouldn't work properly at 70 mph.
If the A/C is doing a good job at 70 mph with lots of cool air flowing over the condensor, I would think the A/C isn't the problem.

Tom Piper

 

I disagree -
Although the main source of heat transfer for the automobile cooling system is from conduction (air/alum/water - which is primary Dependant on surface heat) I think you are forgetting the effects of evaporation (evaporative cooling is humidity dependent) at the A/C condenser which will preheat the incoming air before it passes over the radiator and thereby effectively raise the surface temperature of the radiator, reducing its efficiency (making it work harder) . In that it is my understanding the effects of evaporative cooling are less with humid air than dry air. Therefore the heat of the condenser in front of the radiator is higher (for a given desired cabin temp) in humid air than dry air.

However, I'm no scientist or mech. engineer and certainly could be wrong.. Could you provide any published scientific evidence that humidity has no effect on engine cooling in cars with air conditioning?

My information came from The 9th edition of "mechanical and electrical equipment for buildings" by Benjamin Stein and John Reynolds published by Wiley and Sons, chapter 1 section 2.2-2.6 and chapter 4 section 4.6, chapter 5 section 5.12, and chapter 7 section 7.6-7.9. (Its all I have handy at the time).

BTW: This was an interesting quote which i think pertains to the conversation:

as found on page 39

"As air and surface temperatures approach our own body temp, we lose the options of convection, conduction and radiation. Evaporation becomes essential, so access to DRY moving air is greatly appreciated"

of course this isn't an automotive design guideline resource - but I think the basic physics are the same.

I disagree again - based on personal observation. Just three weeks ago my car was running 240.. I had a bad cap.. a cap isn't necessarily the full 15psi (good) or 0psi (bad - non-pressurized system). Bad caps usually lose spring seat pressure (similar to valve springs that have sat in one position for a long time). which drops the effective pressure of the system.. a bad cap would be anything below the advertised pressure on it.. (i.e. a 15psi cap only preforming to 13psi). The loss in pressure will raise the coolant temp over the higher pressure for a given environmental condition.

When I replaced my cap with a new one my temps went down to the 210* range (or 30* difference). However, at that point my radiator showed its age (176k miles) and blew the gasket on the side tank.. New cap and new radiator and the car runs 180-190* all day long

[/QUOTE]

I'm no car fixing genius but I don't think I would count any of those things out - cap costs $4.95 and your A/C is due for service anyhow.

 

there is greater airflow at 70mph than with the stock fans at idle - which could be mitigating the problem.. Heck Tom, your the expert on the air flow situation on these cars!

 

I think SunCr is talking about a plugged freon system in the A/C.

If the A/C system were plugged up, I wouldn't expect it to work no matter what the airflow over the condensor is.


I could be wrong, maybe he is talking about the condensor being plugged up where the air passes through it.

Tom Piper

 

You are correct that "the effects of evaporative cooling are less with humid air than dry air". However, since there is no evaporation taking place to cool our engines, it doesn't apply to the situation. It is just that simple. Your books and quotes from books, while correct, have no bearing on our cars. You can disagree if you like (you are wrong, however, if you do) but you might as well defend your point with the theory of relativity, as evaporation. The defense of your just evaporated.



Basic physics seldom change. That quote refers to personal, human comfort. Our bodies are cooled, in part, by evaporation. Our cars are not.



Wrong again. I agree that a cap may only partially fail. And I agree that the compromise in pressure in the cooling system may only cause a partial lowing of the boiling point. However, the pressure of the cooling system has no effect on the cooling system temperature. Raising or lowering the coolant pressure does not affect it's temp, when the temp is not at the boiling point for the pressures involved.

RACE ON!!!

 

Next time its hot and humid out and you are running your AC at full blast open the hood and notice the condensation on the condenser and the high pressure lines.. when this evaporates it helps cool the condenser (just like our skin). In dry climates like AZ you don't notice the condensation because it evaporates almost instantly in part due to dry hot air has a higher capacity to hold moisture than humid hot air - hence better evaporative cooling principals. So when you take the gains of evaporative cooling away from the condenser its efficiency is lower which causes it to run hotter, which heats the air before it hits the radiator. the hotter the air that hits the radiator the less efficient its cooling (conductive cooling) and the more taxing it is on the cooling system which it is why I tend to think humidity does have an effect on automotive cooling systems with A/C.

Lets just say we agree to disagree on this one.. and he can make up his own mind!


than I am at a loss to explain my direct personal observations.. The only thing I can think would be that the new cap kept more of the coolant inside the radiator and not in the overflow tank which lead to a higher capacity to remove heat from the engine (more fluid circulating ='s a bigger heat sink)..

 

Hotter air has the capacity to hold more moisture than cool air. Period. Dry hot air does NOT have a higher capacity to hold moisture than humid hot air. Assuming the two air temps are the same the capacity is the same.

The evaporator is cold. It absorbs heat from the air inside of the car. The condenser is hot (with the heat from inside the car) and is cooled by the air stream in the front of car. Condensation you may see on the evaporator and some of the A/C lines is because they are cool, unlike the condenser, which is hot, and the humidity condenses out of the air onto a cool surfaces, just like on your bathroom mirror after a shower. There is no condensation and evaporation taking place on your condenser. It is hot and could it cause evaporation IF there were a liquid present, but since it IS hot, there won't be any liquid forming by condensation onto the condenser. What forces on earth do you propose could cause it to do one the other, simultaneously? You missed the boat in that one.



Since we've seen, above, that there is no evaporative cooling affecting the cooling system, the above is clearly false.



I agree than a loss of pressure could have allowed coolant to escape and that could lead to running hotter, but again, a change of pressure does not change the water temp.

RACE ON!!!