I have a stock '78 L-82 4-speed Daily Driver. Car is all stock but the original fan was replaced with a flex about 1.5 years ago. Car has always run at about 180-190 range suddenly now I'm running around 220 degrees ocassionally creeping up towards 230! What could change overnight? My Chilton told me to see if the upper radiator hose was hot or cool to check thermostat and it was hot, is this accurately telling me the thermostat is good? Help, I need the car to get me back and forth to work everyday......

 

Could be a verity of things, so check the easy ones first. Loose belts or thermostat not opening are the 2 easiest things. Also check that the radiator isn't plastered over with bugs. I don't think a flex fan makes much difference. Yes, the upper hose or the thermostat housing or the radiatior where the upper hose connects should get hot a few minutes after the motor starts. This will tell if the stat is at least opening a little, but may not be opening all the way. A clogged radiatior could also show up suddenly. Fan clutch, etc. Can you see into the radiatior? Try flushing it, but be advised, some flushing chemicals will remove the crud that may be holding it together. Try the detergent type first, then the acid type if needed.

 

how is your water pump??? sounds like that could be the cuplrit IMHO

 

Check coolant level in radiator.Coolant poored in plastic tank doesnt run right in.

 

do u have a front spolier...?

 

No front spoiler, radiator and overflow tank are now full. I had to add almost a gallon when I first noticed temp was up. How can I tell if water pump is working?

 

I was told on an earlier post to check for a 'lean' burn condition which evidently leads to running hot at highway cruise speeds.

So, I looked for vacuum leaks and such on my Vette and here is what I found:

* The carb bolts were so loose that I could slide the carb around some--vacuum leak.

* There was a large slit in the vacuum line controlling the EGR valve--big vacuum leak and no EGR.

* The port where the transmission gets its vacuum signal was very loose--vacuum leak.

I corrected all these and now coolant temperatures are normal. Great advice I got here, thanks!

Yep, I neglected my Vette's regular 'messing under the hood' time because of the classic C3 Catch 22: Get C3 looking and running great to attract and entertain beautiful women-->then when you get the beautiful women, you have no time to work on the C3--C3 rapidly falls apart while neglected--you lose women--now there's time to get the C3 looking and running great.

 

new symptom: lots of gurgling on shutoff. help!!!!

 

did you check the level in radiator not plastic tank?Ok I saw the post

 

the front spolier is a key to stop overheating!!!!!! it lets the car run 10-25 degrees cooler make sure you have one !!!!!

 

you can open the rad cap (while cool) and rev the motor youll see the water flowing if your water pump is good....

 

you can check the waterpump easily enough by feeling the upper radiator hose once the car is at operating temp (at or above the temp of the t-stat). you should not only feel the hose getting hot from the hot coolant running thru it, but you can also feel the flow of the coolant itself. If the hose stayts cool or you don't feel coolant flow than your waterpump isn't operating or the t-stat failed and isn't opening up allowing coolant flow.

now, while everyone is throwing ideas out about how to fix your overheating problem let me first ask you a few questions:

1. does it overheat at idle, or during city/traffic driving, or only on the highway or no matter when?

2. have you checked for vacuum leaks? check for proper timing, check for proper carb adjustment? Timing too retarded makes the can run hot but so does timing too advanced. If your carb fuel/air mixture is too lean it will run hot.

3. Having the stock airdam.spaolier under the front of the nose of the car is very important in cooling. Has it been off for a while or just recently?

4. Did you check your lower radiator hose? with the car off and cool so you can toch it safetly, squeeze the lower hose, especially down by the radiator housing. There is a spring inside to keep the hose from collopsing under pressur. if the spring has failed the hose will collopse easily in your hand and is bad. It means it will collopse while under pressure restricting coolant flow.

5. Using a IR Temp gun did you measure BOTH the temps of the upper radiator hose AND the lower radiator hose. If the car overheats during highway driving (when it's getting the most airflow to it) and the temps on the lower radiator hose are too high than your radiator isn't working properly and needs to be looked at more closely and possibly replaced.

6. have you checked your fan clutch? get the car up to operating temps than shut the car off. The fan should stop within 1-3 revolutions. If it freespins for much more than that it's time for a replacement fan clutch

BTW, not saying that this is your problem, but the flex fans are not as effecient as the stock fans. They don't push as much air for cooling plus they tend to come apart, taking big chunks of fiberglass with it.......
they may look more visually appealing, but they don't operate as well as the stock fans.

 

It could be as simple as your rad cap.

You haven't changed or adjusted anything since the problem started? Right?

Is it only getting hot on the highway? Is the highway drive something new? Fan only cools to about a certain RPM. The shroud and spoiler direct the air flow otherwise. So if your highway driving is something new and you don't have the spoiler thats your problem.

Other possibilites are the water pump and/or thermostat.

Your going to have to provide more detail. Exactly when does it go north of 220?At idle? In the city? On the highway? Does it run at 180 up to a certain point in time? Or does it go straight to 220 at idle and city and highway. All suggest different things.

Jim

 

OK First thanx for all the helpful suggestions.

More detail:

Flex fan has been in car for almost 2 years actually runs approx 10 degrees cooler than with stock clutch fan.

Nothing else has changed on car. One day running 180ish to next day running 220ish spiking to 230+

My daily drive is about 5 miles at 35-40 mph then 55 to 65 for the balance of my daily drive to work.

Temp starts to near 220 about the first five minutes and edges up during highway speeds.

Just noticed something this evening when I went to close the hood that it seems the fan took a small chunk out of the top of the shroud.

It was still too hot to pull off cap to check for flow, I'll check tomorrow but after noticing the shroud I am thinking water pump.

I thought those things made noise when they were going????

 

Chunk out of shroud?check drivers motor mount---did you check to see if your temp gauge is telling the truth?

 

They don't always make noise. You may be on to something with the chunk out of the shroud. Could be the pump, fan or as someone mentioned engine mount.

You can check for the mount by putting it in gear, stepping on the brake, giving it gas and watch for the motor to rise and twist.

As for the temp to be rising so quickly my guess is its cooling system related. Hopefully the "t" stat but more likely the water pump or fan.

Jim

 

Well I had issues with heat over in Tucson and it's looking like my radiator has had it. 25+ years is a long time for a radiator to live. Looked at it today and it looks pretty nasty, too.

 

Some touched on this and I would agree, that if the temps suddenly changed and you didnt' do anything different, I'd first check out the gauge itself. Do you have a mechanical one lying around that you could hook up see, or one of those infared thermometers?

 

Here's a couple more ideas. First, if you have a fan clutch, it might be going bad and not engaging the fan. Second, when you say that you're down on coolant, it could result from a bad intake manifold gasket.

 

Have you changed the radiator cap lately? 78 is a recirculating system and requires fluid in the overflow. Alot of times you here the gurgling after you shut if off is because your radiator is sucking air from a empty recirculating tank. Air in the system will cause the heat.