Ok I will try to give all details so that someone out there will be able to see what I am missing.
The subject is a 68 Camaro with a 71 402 Big Block .030 over. very mild engine.

Car ran great. Had a small block radiator with no shroud but ran 180 in traffic no issues. It went through a mild "restoration" where the roof was replaced and car was painted. I added Vintage air along with a factory replacement new big block radiator with shroud. It now runs hot. 190...then up and up to 220 and I believe it would go further but I have been able to get it out of traffic by that time. It runs hot with the air off, and with it on. It runs ok at speeds of 35 to 50 but the minute you stop it starts to go up. It also gets hot if you are running 70 or above.

Here is what I have done.
New theromstat
2nd new theromstat this time 160 deg
New 600.00 alum radiator ( This one is much bigger that the Big Block and 3 tyimes the size of the small block one)
new temg gage ..just to see if it was reading wrong
Tested by cranking engine with radiator cap off to see when thermostst opened up and if water was flowing. You can see the flow in the radiator.
New radiator cap
New overflow tank

remember this is a car that ran cool with the wrong radiator and no shroud. It now runs hot even if I remove the belt from the AC. No chance to run AC unless you are driving the 35 to 50 speed with no stops.

I have added an electric pusher fan to the front side of the AC coil just as Vintage Air told me to do. I have made a air shield between the radiator and the core support so that all air must go through the radiator.

I am runnung a 18" 6 blade mechanical fan with no clutch because the long waterpump of the 71 model engine in a car that had a short pump will not allow for the clutch.

The fan is a high flow stainless unit.

As you can see I have spent many hours and dollars to get to this point. I am ready for your ideas and hope that someone here will see what it is that I have missed.

THANK YOU IN ADVANCE FOR ANY HELP. As you can tell, I have no more ideas. You can contact me direct at mark_sanders@bellsouth.net or respond here.

wheres the fan sitting in to relation of shroud.also in order to replace heater box needed to remove passenger side fender correct?or inner wheelhouse. when they put it back together did they put seam sealer from cowl to fender. that will not allow air to flow out of engine compartment.when you did a/c conversion did you put your temp sensor in different spot also.did you take out by pass hose also. just some thoughts for you. what happened after the conversion you did.

Great questions..Thanks

The fan sits about 1" from the radiator and the blades are about 1/2 way in the shroud. The fenders were both off for the body work and the factory heater box was removed. There was no seam sealer added in the fender area. The Vintage air plate is sealed to the firewall per the instructions. The temp sensor goes into the drivers side head. I have since removed it and installed it in the intake. I even had 2 temp gages in at one time to see if that was an issue and the temp from the head or the intake was the same. The car had 2 bypass hoses on it and I did remove one so that I could install the heater hoses. The heater works and blows hot air and the bypass hose that is still there is the one that is closest to the drivers side.

Thanks for the help. If you see anything here that I need to check, please tell me. I do not pretend to be a mechanic, only a hobbiest. THANKS Mark

you just about threw all my sugestions out the wall. 1 last thing where does that by pass hose goes to. i cant help on that since i dont have a big block.but pictures may help. i know people with big block 68 and 69 cars.i took over a 1000 pictures while redoing my 67. some help others and alot dont.theres soo much to a car that you can amagine.

Is this the same fan you were running before?

As thorough as you are, I bet you've already checked this...
Any chance the distributor got moved while all the work was going on? Retarded timing will get them hot.

Did all your pulley sizes for the water pump and fan stay the same when you added AC?

Guys thanks...The bypass hose is in the righ place for sure. The pulleys did not change during this deal and I have changed the timing 10 times trying to see if any changes are made. Keep thinking guys, my brain hurts and I am out of ideas. If I had the cash I think I would buy a small block to go in there...............Oh no what am I saying? ha ha

THANKS MARK

I can only come up with one way to troubleshoot it without buying electric fans plural. And that is to remove the condenser and test drive it. I hope somebody with a better idea comes along.

I'm not into car fans and I know there's lots of flavors available. I think JimM was headed somewhere with his question.

My junk we just increase the blade pitch or increase the quantity of blades or speed them up to fit the job. Keep the fan tip speed at around 13,000 FPM. Next week I kick off a job where I am throwing away a 20,000# cooler with an 11' fan and putting a bigger cooler with either a 12 or 13' fan I forgot.


You didn't bolt your fan on backwards by any chance?

Is this the same fan you were running before?

?

Same fan as before and it is bolted on the right way. The bypass hose is there also.

I hate to remove the ac condensor for a test because that means recharging it after and as was said there are plenty of BB with AC so this should work. Even Vintage Air has run out of ideas for me????
Mark

You've added a top plate between the header and core support, good. Did you add one from the bottom valance and core support? Heavy poster board and duct tape would be a good science project just to see. Anything you can do to prevent/cut down recirculating hot air.

No need in pulling the AC condensor. Higher pressure rad cap?

I believe the fan, 6-blade 18 in dia is good, but, it is driven faster than crankshaft rpm, by 30%? If w/pump pulley is 6 inch, you need a 7.5 or 8 inch crank pulley.

High flow thermostat? MRG-4364? A Stewart water pump maybe next.

Hi, A couple of thoughts. You have to be careful as to the mixture of antifreeze and water . If you have more than a 50/50 mix of antifreeze you can have an overheating problem. Antifreeze doesn't absorb heat from the engine as well as water. The greater the concentration of antifreeze beyond 50/50 the greater the overheating. Also a radiator hose that has to sharp a bend can cause a problem as can a hose that is soft and closes at speed. Lew

You could possibly have an air pocket somewhere in the engine. Have you burped the system?

The "runs hot below 35 mph" clearly indicates that for whatever reason, the fan is not pulling enough air thru the core.

Try one of these: http://store.summitracing.com/partdetail.asp?autofilter=1&part=DER%2D17018&N=700+4294838812+115&autoview=sku for forty bucks, what have you got to lose?

No comment on "over 70" as I have no info on gearing...

You could possibly have an air pocket somewhere in the engine. Have you burped the system?

That's what I have been thinking.

In addition, I have a question. You mentioned the distance from the radiator, and the distance the fan is inside the shroud.
What is the distance from the fan blade edges to the shroud?

OK,,,here are a few answers to some of your responses. First THANK YOU VERY MUCH for your ideas. I have the fan from Summit like was suggested. I have never heard of burping the system and even though I do not believe I have air trapped in the system, I can not be sure. Please tell me how to burp the system. The antifreeze is about 60% water and 40%antifreeze. I have never used any type of radiator leak stuff in this system and it is clean inside. I have not built a cardboard and duct tape air dam but will try that also. I have put on a replacement cap at a higher pressure and an overflow tank also. No sharp bends in the hoses, in fact they are new. I do not know the diameter of the pulley but can check it tonight.

As for a clutch fan or electric fans. The distance between the water pump and the radiator is a little less that a normal 1968 car because I have the long water pump on the car. All of the brackets to mount the AC, power steering , alternator are like would be on a 69 Camaro. This makes it where you can not put a standard 69 fan clutch on the car.

GUYS...KEEP THINKING. I really do appreciate every idea. I promise to check everything you guys tell me to and I will report on my findings. This is only a machine and I will win. Mark

Like Jim M said, what rear gearing are you running? I am experiencing the same issues except only at highway speed, but mine is because of my gearing. Could it be the pusher installed in front blocking air flow? Factory setups only used a single fan, even on the big blocks. Didn't they? What about obstructions behind the radiator that isn't allowing the hot air to escape? I have a long water pump and am using a fan clutch. Mine is a small block. Is there less room between the pump and fan on a big block as opposed to the small block?

The "runs hot below 35 mph" clearly indicates that for whatever reason, the fan is not pulling enough air thru the core.

I agree with Jim, you are having an air flow problem. Could you post some pictures of the set up this would really help. How much room is between the condenser and the radiator? How many rows is the radiator and what brand is it? What size and brand is the pusher fan on the condenser. Does the pusher fan work all the time or is it themo controlled. Are you using a stock long water pump?

Also at 70 mph (depending on gearing) your engine will generate more heat as RPM's increase. That fan will flatten out at higher RPM's and not pull as much air through, it could be why there is a rise in temps at 70 mph.

I am sorry I forgot to answer the gear ratio question. The rear is a standard Big block automatic rear. That makes it single traction and a gear ratio of 3:08.....nothing fancy here. It was in the car when it was an automatic, but is now a muncie 4 speed. The pusher fan is 16" and is set up like Vintage Air said to. It runs only when the compressor is running. Hooked to the bianary switch. But keep in mind I was running hot even with the air off and I did not have this second fan on the car. I can not tell if adding it has helped at all or even hurt the problem.
Water pump is stock. I was thinking about a new one that is high volume but have not done that yet. This pump has 5000 miles on it and worked before the changes.

Let me ask one more question here.....there is a vacuum line that goes to the mod valve on the auto trans. When I converted to 4 speed, I just plugged it up. Could there be a vacuum issue with the timing? I can check timing at idle but really do not know what happens when the car is running. It starts easily, dose not run on when the key is turned off and is not slow starting unless the car is really hot. This is a very mild engine. stock 402 + .030

I have no idea about the clutch fan from a small block, but I do know that I purchased the complete set up for a 69 Camaro and it would not fit and that was before I put the new radiator in. The new radiator is a Griffin 4 core aluminum. Thanks Again......Mark

Mark, as a test I would try turning the electric fan on at 180 degrees but with the A/C off and see if it keeps the temp down. You could use a toggle switch for this test. If this helps keep temps down then you know it is an air flow problem. Does the shroud completely cover the radiator core?

After reading your post again it sounds like everthing was the same except the addition of the A/C system. The condenser could be blocking enough air flow that the old components just can't handle it. I would still check the pulley size on the pump and the crank, a smaller water pump and bigger crank pulley will speed up the fan and pull much more air. Just some more ideas for you.

I will work on some answers for you guys , like the pulley sizes and I will run a test with the electric fan on at 180 deg to see if that helps. THANKS SO MUCH. I will let you know ASAP. Mark

OK here is the story today. It was not very hot in Atlanta today, only about 85 deg but it has been in the high 90's lately. John Z had mentioned in his post to me that I needed to move the vacuum line going from the dist to full manifold vacuum. I did this and ran a test today. No other changes made. Drove 30 miles in expressway and stop and go traffic. Same trip as 2 days ago when it went to the point of boiling the gas out of the fuel filter. I turned the AC on full blast and left work and did not turn it off until I pulled into my driveway. The temperature never went over 185 deg. The only thing that I have to add to this is I wish I had of asked more questions before I bought a 600.00 radiator. THANKS EVERYONE........THANY YOU VERY MUCH JohnZ

Mark Sanders Atlanta GA

Just made it back from a 500 mile trip to the Shades of the Past car show in TN. Had a few small issues, but nothing really. The highest temp of the whole week end in HEAVY traffic was 210. I did have a problem with vapor lock one time and will give those details later, but for now I have to go to work. THANKS again for all of the help. I am sure that I would never have figured this one out on my own. Mark

Mark, Are you using a Vintage Air Frontrunner system?
If not, is the bypass hose attached? It should come out the top of the water pump and into the intake manifold, below the thermostat. Be sure it is connected otherwise air will get trapped. What brand of water pump are you using? Also with the temp sender in the intake, what is your temp reading?

"It runs ok at speeds of 35 to 50 but the minute you stop it starts to go up. It also gets hot if you are running 70 or above."

This sounds like a airflow and/or water flow issue. Check the pulley diameters to be sure you are not underdriven, let me know if you are not sure how to do this.