C4 Running Hot
1st Gear
Joined: Jun 2015
Posts: 1
Likes: 0
C4 is running hot
My C4 dash gauge also showed that it was running hot. It would cool down when I ran the AC because as soon as the AC is turned on the cooling fans kick in. My mechanic hooked up his scanner to my cars computer and it showed that my car was running much cooler than the gauge was showing. He then showed me how to turn on the digital readout of the engine temp in my gauge cluster. It showed the correct temperature not the temperature displayed by the gauge on my dash. Your car may not be running hot - it is probably the gauge being inaccurate.
Safety Car
Joined: Aug 2006
Posts: 4,147
Likes: 452
From: Port St. Lucie West Florida
You just answered your own question on the airflow. That is exactly why they run so much hotter while sitting in traffic. In order to run cooler, requires airflow through the radiator.
To get airflow requires one of two things:
1. Car has to be moving greater than approx. 40mph
2. The electric cooling fans need to be running
It's a well known fact that the factory settings for the cooling fans won't command them to come on until temps. are in the upper 220 range. Note: You can also turn on the A/C and they should come on.
This is one car that will actually run cooler with the A/C on (assuming your cooling and A/C system is in good condition).
So, if you want your car to idle in traffic cooler than 190-200 range your going to have to modify your cooling system from what the factory had set.
220 - 230 while sitting in traffic is not too hot for a modern well maintained cooling system though. It's too hot for some people to live with, but that's the way they left the factory.
To get airflow requires one of two things:
1. Car has to be moving greater than approx. 40mph
2. The electric cooling fans need to be running
It's a well known fact that the factory settings for the cooling fans won't command them to come on until temps. are in the upper 220 range. Note: You can also turn on the A/C and they should come on.
This is one car that will actually run cooler with the A/C on (assuming your cooling and A/C system is in good condition).
So, if you want your car to idle in traffic cooler than 190-200 range your going to have to modify your cooling system from what the factory had set.
220 - 230 while sitting in traffic is not too hot for a modern well maintained cooling system though. It's too hot for some people to live with, but that's the way they left the factory.
Racer
Joined: Mar 2014
Posts: 409
Likes: 7
From: Taunton MA
Just a few thoughts on this very good thread:
1. Just because a business puts Corvettes in their name Doesn't mean they are Corvette specialists. Near me there a local business called Corvettes and Classics, I used them ONCE, let's just leave it at that.
2. Illenema is right on (IMO) with having both fans come on, I had my computer reprogrammed for both fans to come on at 205 degrees.
3. I would not get the Bi-metal switch that you screw into the head to activate the fan (the plug that needs to be taken out can be difficult to remove), have the car reprogrammed.
4. My vette also has temp. spikes while sitting in traffic. When I come off the highway (running about 197) then stop at a light it climbs fast. Pretty normal when the air temp is 80+.
5. All the little things mentioned are great advice. Clean the AC and radiator, check the lower hose, and the temp sensors.
Just my thoughts...
C
1. Just because a business puts Corvettes in their name Doesn't mean they are Corvette specialists. Near me there a local business called Corvettes and Classics, I used them ONCE, let's just leave it at that.
2. Illenema is right on (IMO) with having both fans come on, I had my computer reprogrammed for both fans to come on at 205 degrees.
3. I would not get the Bi-metal switch that you screw into the head to activate the fan (the plug that needs to be taken out can be difficult to remove), have the car reprogrammed.
4. My vette also has temp. spikes while sitting in traffic. When I come off the highway (running about 197) then stop at a light it climbs fast. Pretty normal when the air temp is 80+.
5. All the little things mentioned are great advice. Clean the AC and radiator, check the lower hose, and the temp sensors.
Just my thoughts...
C
Melting Slicks
Joined: Jul 2005
Posts: 2,649
Likes: 863
OK - A lot of info in this thread - some very good - some questionable...
On LT1/LT4 equipped C4's the PCM controls the fans. The first fan typically comes on around 220 - the 2nd one around 230 - IF the A/C is off. If the A/C is turned on - one fan will be running.
The C4's have pretty poor airflow to the radiator compared to many cars - but once the car is doing 35 - 40 MPH - there is normally enough airflow through the radiator that the fans aren't necessary meaning that if you are seeing a car running hot at highway speeds - the fans aren't the problem.
The thermostat only controls the temp at which coolant is allowed to Start flowing to the radiator. If you are seeing temps over 210 degrees, the thermostat should be full open - and it's rating is utterly unimportant.
In my opinion - much over 235 is just too hot. I'd say that at the 250 mark you're getting very close to the danger zone.
So - let's start by figuring out what's really going on. Does the analog gage reading match the dashboard digital display's - coolant temp reading ???
Get (borrow) an IR temp gun, and when you see a 250 degree coolant reading - pop the hood and see what the IR gun reads the temp of the upper radiator hose. The two temp readings may not be exact matches - but they should be close. If the temps don't match, the chances are that you have a defective temp sensor. If they do match reasonably well - you need to keep digging.
The one thing that many people forget about C4's is that they tend to have a propensity to collect "junk" between the radiator and the A/C coil. You can have the best fans in the world - but if there is any crud built up in there it will restrict airflow to the radiator, and that WILL diminish cooling (ask me how I know this). I know you said you had a new rad installed, but if you didn't do it yourself - you don't know if the place that installed it did a thorough job of cleaning that area out. If you have that IR temp gun - you can look at the temp drop of the coolant across the radiator. With the fans running - check the coolant temp going to the radiator, and then go down under the front pass side of the car and see what the temp of the lower radiator hose is. There had better be at least a 20 degree drop - if not - there is either insufficient flow through the radiator (clog, bad hose, or bad water pump) - or not enough air is flowing across the radiator.
Personally - I think that the factory programmed the fan "on" temps too high - I expect that it was done for emissions purposes. Reprogramming the PCM to turn the fans on sooner or installing a switch that allows you to manually turn on the fans makes some sense to me - particularly if you live in a very warm area. But - even with the factory PCM settings - you shouldn't be seeing the kinds of temps that you are reporting.
GOOD LUCK !!!
On LT1/LT4 equipped C4's the PCM controls the fans. The first fan typically comes on around 220 - the 2nd one around 230 - IF the A/C is off. If the A/C is turned on - one fan will be running.
The C4's have pretty poor airflow to the radiator compared to many cars - but once the car is doing 35 - 40 MPH - there is normally enough airflow through the radiator that the fans aren't necessary meaning that if you are seeing a car running hot at highway speeds - the fans aren't the problem.
The thermostat only controls the temp at which coolant is allowed to Start flowing to the radiator. If you are seeing temps over 210 degrees, the thermostat should be full open - and it's rating is utterly unimportant.
In my opinion - much over 235 is just too hot. I'd say that at the 250 mark you're getting very close to the danger zone.
So - let's start by figuring out what's really going on. Does the analog gage reading match the dashboard digital display's - coolant temp reading ???
Get (borrow) an IR temp gun, and when you see a 250 degree coolant reading - pop the hood and see what the IR gun reads the temp of the upper radiator hose. The two temp readings may not be exact matches - but they should be close. If the temps don't match, the chances are that you have a defective temp sensor. If they do match reasonably well - you need to keep digging.
The one thing that many people forget about C4's is that they tend to have a propensity to collect "junk" between the radiator and the A/C coil. You can have the best fans in the world - but if there is any crud built up in there it will restrict airflow to the radiator, and that WILL diminish cooling (ask me how I know this). I know you said you had a new rad installed, but if you didn't do it yourself - you don't know if the place that installed it did a thorough job of cleaning that area out. If you have that IR temp gun - you can look at the temp drop of the coolant across the radiator. With the fans running - check the coolant temp going to the radiator, and then go down under the front pass side of the car and see what the temp of the lower radiator hose is. There had better be at least a 20 degree drop - if not - there is either insufficient flow through the radiator (clog, bad hose, or bad water pump) - or not enough air is flowing across the radiator.
Personally - I think that the factory programmed the fan "on" temps too high - I expect that it was done for emissions purposes. Reprogramming the PCM to turn the fans on sooner or installing a switch that allows you to manually turn on the fans makes some sense to me - particularly if you live in a very warm area. But - even with the factory PCM settings - you shouldn't be seeing the kinds of temps that you are reporting.
GOOD LUCK !!!
Burning Brakes
Joined: Nov 2013
Posts: 914
Likes: 277
From: St. Petersburg FL
OK - A lot of info in this thread - some very good - some questionable...
On LT1/LT4 equipped C4's the PCM controls the fans. The first fan typically comes on around 220 - the 2nd one around 230 - IF the A/C is off. If the A/C is turned on - one fan will be running.
The C4's have pretty poor airflow to the radiator compared to many cars - but once the car is doing 35 - 40 MPH - there is normally enough airflow through the radiator that the fans aren't necessary meaning that if you are seeing a car running hot at highway speeds - the fans aren't the problem.
The thermostat only controls the temp at which coolant is allowed to Start flowing to the radiator. If you are seeing temps over 210 degrees, the thermostat should be full open - and it's rating is utterly unimportant.
In my opinion - much over 235 is just too hot. I'd say that at the 250 mark you're getting very close to the danger zone.
So - let's start by figuring out what's really going on. Does the analog gage reading match the dashboard digital display's - coolant temp reading ???
Get (borrow) an IR temp gun, and when you see a 250 degree coolant reading - pop the hood and see what the IR gun reads the temp of the upper radiator hose. The two temp readings may not be exact matches - but they should be close. If the temps don't match, the chances are that you have a defective temp sensor. If they do match reasonably well - you need to keep digging.
The one thing that many people forget about C4's is that they tend to have a propensity to collect "junk" between the radiator and the A/C coil. You can have the best fans in the world - but if there is any crud built up in there it will restrict airflow to the radiator, and that WILL diminish cooling (ask me how I know this). I know you said you had a new rad installed, but if you didn't do it yourself - you don't know if the place that installed it did a thorough job of cleaning that area out. If you have that IR temp gun - you can look at the temp drop of the coolant across the radiator. With the fans running - check the coolant temp going to the radiator, and then go down under the front pass side of the car and see what the temp of the lower radiator hose is. There had better be at least a 20 degree drop - if not - there is either insufficient flow through the radiator (clog, bad hose, or bad water pump) - or not enough air is flowing across the radiator.
Personally - I think that the factory programmed the fan "on" temps too high - I expect that it was done for emissions purposes. Reprogramming the PCM to turn the fans on sooner or installing a switch that allows you to manually turn on the fans makes some sense to me - particularly if you live in a very warm area. But - even with the factory PCM settings - you shouldn't be seeing the kinds of temps that you are reporting.
On LT1/LT4 equipped C4's the PCM controls the fans. The first fan typically comes on around 220 - the 2nd one around 230 - IF the A/C is off. If the A/C is turned on - one fan will be running.
The C4's have pretty poor airflow to the radiator compared to many cars - but once the car is doing 35 - 40 MPH - there is normally enough airflow through the radiator that the fans aren't necessary meaning that if you are seeing a car running hot at highway speeds - the fans aren't the problem.
The thermostat only controls the temp at which coolant is allowed to Start flowing to the radiator. If you are seeing temps over 210 degrees, the thermostat should be full open - and it's rating is utterly unimportant.
In my opinion - much over 235 is just too hot. I'd say that at the 250 mark you're getting very close to the danger zone.
So - let's start by figuring out what's really going on. Does the analog gage reading match the dashboard digital display's - coolant temp reading ???
Get (borrow) an IR temp gun, and when you see a 250 degree coolant reading - pop the hood and see what the IR gun reads the temp of the upper radiator hose. The two temp readings may not be exact matches - but they should be close. If the temps don't match, the chances are that you have a defective temp sensor. If they do match reasonably well - you need to keep digging.
The one thing that many people forget about C4's is that they tend to have a propensity to collect "junk" between the radiator and the A/C coil. You can have the best fans in the world - but if there is any crud built up in there it will restrict airflow to the radiator, and that WILL diminish cooling (ask me how I know this). I know you said you had a new rad installed, but if you didn't do it yourself - you don't know if the place that installed it did a thorough job of cleaning that area out. If you have that IR temp gun - you can look at the temp drop of the coolant across the radiator. With the fans running - check the coolant temp going to the radiator, and then go down under the front pass side of the car and see what the temp of the lower radiator hose is. There had better be at least a 20 degree drop - if not - there is either insufficient flow through the radiator (clog, bad hose, or bad water pump) - or not enough air is flowing across the radiator.
Personally - I think that the factory programmed the fan "on" temps too high - I expect that it was done for emissions purposes. Reprogramming the PCM to turn the fans on sooner or installing a switch that allows you to manually turn on the fans makes some sense to me - particularly if you live in a very warm area. But - even with the factory PCM settings - you shouldn't be seeing the kinds of temps that you are reporting.
I think Purple92 has given you some of the best areas to take a look at. And, I agree with him that 235° is just too hot to ignore.
Besides checking your "Be Cool" radiator to make sure it's doing what it's supposed to and... that the area surrounding the condenser (forward of the radiator) is clear of debris, I would recommend changing out your "knock Sensors" on either side of the engine block and flushing the engine. If the knock sensors weren't pulled when you installed your new radiator, your may have left your block full of debris.
Drifting
Joined: Aug 2009
Posts: 1,969
Likes: 242
The temps the OP describes sound pretty normal to me for an LT1.
I reflashed the PCM in my 94 to change the fan temps. I rarely see 200 degrees now, even in summer traffic. That said, the fans run a whole lot more.
I reflashed the PCM in my 94 to change the fan temps. I rarely see 200 degrees now, even in summer traffic. That said, the fans run a whole lot more.
Advanced
Joined: Dec 2006
Posts: 76
Likes: 1
From: Port St Lucie FL
The one thing that many people forget about C4's is that they tend to have a propensity to collect "junk" between the radiator and the A/C coil. You can have the best fans in the world - but if there is any crud built up in there it will restrict airflow to the radiator, and that WILL diminish cooling (ask me how I know this). I know you said you had a new rad installed, but if you didn't do it yourself - you don't know if the place that installed it did a thorough job of cleaning that area out.
Intermediate
Joined: Feb 2017
Posts: 33
Likes: 1
From: Oxford Conn.
Hot C4
My 1985 gets up to 203 degrees before the electric fan comes on. Occasionally it will go a little higher than 203 before the fan comes on. After the fan comes on, the temp goes down atleast 5 degrees.
I never changed the thermostat or hoses in the 2 years I had the car, but I flushed the coolant out at least 6 times to get rid of all the rusty water. I then put a stock radiator in from Autozone. Anything aluminum and double or triple core is too thick and would require cutting and it would be too close to the ac compressor radiator. Under the radiator was at least a plastic grocery bag full of debris and leaves.
After the final radiator flush and new 50/50 coolant and removal of the debris, and the correct amount of coolant in the newly cleaned reservoir, the car still runs the same temp. 185-195 on a moderately warm day and still around 203-210 on a very hot day.
What is interesting is with the roof removed, the engine runs a few degrees cooler.
I heard advancing the timing will make the engine run cooler. I also heard that retarding the timing will make the engine run cooler. Being that my car does not ping and has decent acceleration, I think I'll opt to leave the timing alone. SHARKFACE
I never changed the thermostat or hoses in the 2 years I had the car, but I flushed the coolant out at least 6 times to get rid of all the rusty water. I then put a stock radiator in from Autozone. Anything aluminum and double or triple core is too thick and would require cutting and it would be too close to the ac compressor radiator. Under the radiator was at least a plastic grocery bag full of debris and leaves.
After the final radiator flush and new 50/50 coolant and removal of the debris, and the correct amount of coolant in the newly cleaned reservoir, the car still runs the same temp. 185-195 on a moderately warm day and still around 203-210 on a very hot day.
What is interesting is with the roof removed, the engine runs a few degrees cooler.
I heard advancing the timing will make the engine run cooler. I also heard that retarding the timing will make the engine run cooler. Being that my car does not ping and has decent acceleration, I think I'll opt to leave the timing alone. SHARKFACE
235 is on the warm side but overall, not too bad. 210 is OK for freeway if the air temps are high. What temperature thermostat was installed? Did they replace the pressure cap? Is the coolant level at the proper height in the tank? It should be just below the rim of the opening.
Is there fluid in the overflow bottle and is it at the correct mark for hot at operating temps or at the mark for cold before the engine is started for the first time in a day?
Did they replace the radiator coolant hoses? The lower hose may be collapsing and causing a drop in flow of coolant.
The radiator should be fine to provide the amount of surface area to cool the motor. But is the motor stock? Lots of mods like a cam, compression, bigger displacement could put more of a load on the cooling system.
Did the clean out the A/C condensor coils to allow for sufficient airflow through it so that the radiator can work?
When you turn the A/C on , does the secondary fan start?
Is there fluid in the overflow bottle and is it at the correct mark for hot at operating temps or at the mark for cold before the engine is started for the first time in a day?
Did they replace the radiator coolant hoses? The lower hose may be collapsing and causing a drop in flow of coolant.
The radiator should be fine to provide the amount of surface area to cool the motor. But is the motor stock? Lots of mods like a cam, compression, bigger displacement could put more of a load on the cooling system.
Did the clean out the A/C condensor coils to allow for sufficient airflow through it so that the radiator can work?
When you turn the A/C on , does the secondary fan start?
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