This is an update to my earlier post. http://forums.corvetteforum.com/zerothread?id=319433

Did the small fan clutch test and mentioned. It failed. When engine was cold, the fan turned easily. Took it out, and then tested it again hot. It still turned easily. So I need a new fan clutch. I have seen fan clutch replacements for earlier model C3's that make the fan turn faster by elminiating the clutch all together. Do they make these for '77s and would that help? I am going to try drilling the holes in the thermastat because I also saw that in this month's Super Chevy Mag. Also took it out for high speed testing today. It reached about 230-240.

I also mentioned earlier that I do not remember having a spring in the lower radiator hose. I looked at it today while it was hot and running and it did not look collapsed at all. Main radiator seals are in place. PLEASE HELP! THIS IS GETTING TO THE POINT OF ANNOYANCE!! :mad

 

Personally, I wouldn't let my engine get that hot. When my engine reaches 230 degrees it's time to shut her down. Did your engine reach 230-240 degrees during highway driving?

Your lower radiator hose will most likely not collapse during idling conditions. It will collapse on you while you are driving down the highway. This could be where your overheating problem lies. There are fans available that eliminate the clutch fan. Flex-fans are bolted directly to the water pump. I would honestly rather run a good clutch fan than a flex-fan though.

 

The spring in the lower radiator hose would simply be a device to prevent hose from collapsing in on itself, but I agree that it is not likely the problem. I would double check the sender as Chuck mentioned in the previous post. I would also look into the radiator. Was it brand new, recored? How many rows? Could the water pump be bad? (not likely, but it happens)

I would definitely try to check out each item previously replaced. I made all of the same changes on mine - radiator, water pump, hoses, sender, thermostat and run at 150 degrees even on 50 mile drives in 110 heat.

Also, are the lower valance and chin spoiler there? There is the possibility that not enough airflow is being directed to the front of the radiator. (I did remove my front license plate bracket (since I can legally).

 

Look if you can't solve the problem yourself take it to a pro. Don't mess around with a sick cooling system or you will detroy your engine. 99% of cooling problems can be traced to a blocked rads or a Bubba removed the overflow tank and by-pass hose.

 

Did you check the accuracy of your gauge yet? Simple things first! My new sender read 240 when only 200 degrees actual. Boil a pot of water and immerse the sender in it, make sure your key is in "on" position. Use a cooking thermometer to varify temps. But if the gauge is showing temperature above 212 degrees and the water is not boiling, you can be assured that the gauge is reading high!

Chuck

 

What thermostat did you use (I'm going ot a 160), what radiator are you using-stock brass and copper three roller? aluminum? four roller? stock water pump or one of the super flow water pumps?
Thanks,
Bill :confused:

 

do you have the original exhaust system on it? if so, you may have a clogged muffler/ catalytic converter... causing excesive back preasure... makin you engine overheat...

The other one to check is the rubber gasket around the top of the radiator... and if you have a/c pull off the condensor and check to see if its got a few lbs of leaves stuck inbetween the rad and the condensor... mine did...

Hope this helps, or gives ya an idea...

ZD

 

Have you checked your idle mixture? Your car may be running too lean/rich. My engine temps dropped about 20 deg. when I got the mixtured dialed correctly.

Seriously -- take it to a pro. I paid $50 to have the radiator flushed, replaced the upper and lower hoses, new 180 thermostat and the car runs fine. My "overheating" problem turned out to be a bad sending unit (as we all know, any new sending units, at least for the early cars, reads 20 - 60 deg off depending on what you get). When I had the radiator flushed the guy took a temp reading off the upper hose and said I confirmed that my problem was just the guage misreading.

The cooling system is actually pretty straightforward and there are only a couple of places things could be going wrong.

1. Make sure you have ALL your radiator seals
2. Make sure your fan clutch is working (which you know it isn't)
3. Check your hoses.
4. Check your pump and thermostat
5. Your guage is bad

 

Thermo is 160. Everything else is new, just stock replacement though. I ran into a guy today at Burger King and I had a little talk with him while I was eating. He admitted that he didn't know a WHOLE lot about cars but he knew a little from some racing that he did. He said something about it running hotter because my engine is bored out. I do have a slight bore but because its nothing big, it shouldnt make the big of a difference.....right?!

 

Johnny

Just read your entire post. I'm willing to bet 100% that the problem is the sending unit. I as on a Jihad to find the right sender to no avail. That's when I found out, not only on this forum, but from two separate local Corvette shops, that 99% of the over-the-counter senders are wrong. There is one manufacturer of these (even for AC Delco), and they are calibrated badly.

Here's are 2 REAL simple tests. Have a pro confirm but this will get you close.

1. Drive the car until you see the temp go up to the 240 mark. Pull over and turn the car off, then IMMEDIATELY turn the key back to the "on" postion (don't start the car). I bet that the guage will jump down to 190 deg. That's test #1.

2. Open the hood and get out of the car. Grab the upper radiator hose with your hand. It will be hot. How hot is the queston
- If it's in the coorect operating range it will be uncomfortable, but you should be able to grip it for a few seconds.
- If it's running really hot (say at 240), you won't be able to touch it for a second.

That's the best way I can tell you to test for a bad sender. If it is bad, take it to a radiator shop and have them check the temp. Then you'll be able to know how far off your guage is.

 

I have turned it off before and then turned it back to the "on" position. It stays at the high temp. I'm not sure if I want to go and grap the hose when it is hot. Sounds painful. I am going to drive it tonight and I definately am going to test the water with a kitchen thermometer. I am also going to go ahead and order complete replacement raditor seals, the air dam that goes underneatch, and check the spark plugs for a mixture problem. Thanks to everybody who has contributed so far. But please feel free to add your 2 cents.

 

I don't literaly mean "grab the hose until your hand burns", but seriously, after you stop the car open the hood and touch the hose. If it's slightly uncomfortable but bearable you're probably fine. If you can barely even touch it, then that will tell you.

Since you're grabbing rubber you're not going to hurt yourself, but it will give you a good indication. There is a BIG difference between 180-200 deg and 220+. Your body will know.

 

Hay, is this true about the not being able to rotate the fan when it cold? I thought you could turn it but it would have some resistance to it. Also, I thought that the fan clutch was setup to disengage when it reached a certain RPM not temperature..:confused: :confused:

 

Corellian,

I followed your advice to check my radiator hose. I burned my hand with 3rd degree burns. My attorney would like to have your address to send you some reading material. Oh, THE PAIN, the psychological distress! :cry

A new matching ZO6 for my wife would help the pain go away :smash: :lol:

Chuck

 

There are two types of clutches. Some work depending on rpm some work on rpm and temperature.

 

Does anyone know what years had what if this is the case? I would love to kow what mine is, I checked mine and it rotates when its cold (with some resistance) and I would have thought that mine would be of the RPM type clutch.

 

If you decide that you need a clutch, I have a nice one with a seven blade fan that I can sell at a reasonable price to help you out.
will_shepherd@hotmail.com

 

Actually, I think that you should be able to turn it easily when its cold and it has alot more resistance when its hot. If you think about it, its makes quite a bit of sense. It sort of works like the thermometer and the choke. When it is cold, the spring is compressed and allows the fan to turn freely. This is that way so the fan doesnt start spinning at the same speed of the engine. That way the engine warms up faster. But once it gets hot, the spring expands, and applies more resistance to the fan and grasps it. That way the fan starts turning as fast and the engine does and it brings in more air to help cool it.

I did some shopping for a new clutch and those things can get pretty expensive. I also looked at getting a flex fan. They have no parts that can fail on you like a clutch fan does and they cost half as much. I can get the fan and the spacer for about $35 where the clutch alone cost me like $70.

Is there anybody here that has a flex fan on their engine?

 

I was told that the clutch was totally dependent on engine RPM and not temperature. As the RPM comes up (as it would when you are driving at lets say 50 MPH) the fan would not be needed and the clutch would disengage the fan. I was also told that if the fan was running, it would actually interfere with the flow of air and make it run hotter.. :confused:

 

Over and over I am reading how everbody thinks its this and that. 160 Thermo may be to low for you.
Take this under consideration.
Your radiator is cooling the water while the engine is heating it up.
When your engine reaches 160 the thermo opens taking cool coolant from the rad to the engine and theoretically the thermo closes and gives the rad time to cool the hot water from the engine. Problem alot of times is your car may never run down to 160 without a Be Cool or Griffing Rad and your thermostat is staying open not cooling the water long enough in the radiator and by removing the thermo or drilling it you are just making the problem worse. Try stepping up to a 175 or 185 thermo. You will run cooler. I know these cars always ran hot and GM routinely set cars up to run around 200-235. 84-92 Trans Am and Camaro ran 225 all day long.
Jetting and timing make a huge difference on temp also.
Find the fan clutch for the biggest motor with AC and all Power Accessories for your year. Mine for 1972 is 2 inches thick and a monster clutch.


[Modified by subboz, 3:47 AM 7/5/2002]