You would have thought the high temp problems would have went away with a complete engine rebuild, new performance water pump, new radiator, and two different t-stats (first 180 then 160). Since it is a new motor (maybe an hour or two run time), I haven't let it get too hot. However, with a digital thermometer measuring water temp at the water neck, I have shut the motor down at 210 degrees and rising with it just idling. I realize that's not overheating completely (yet) but it's way too hot for 700 rpms in the driveway. I can see coolant flowing through the radiator. Fan shroud is in good shape. I can feel what seems to be a lot of heat blowing off the fan for just idling. I am confused. I rebuilt the original motor with minor changes.

Any Ideas? Thank You for the Help!!!

350 +.030"
882 stock heads
comp extreme energy cam 262
performer intake
long tube headers
holly 4150 carb
new OE 3 row brass radiator (I think this might be the problem)
6 blade flex fan
tuff stuff water pump

 

Over heating problems can be tough but go back to the simple things first.
1, you are running a thermostat, right, do not run without one.
2, check to see that the fan is properly installed and is about half way into the shroud. when idling you should feel a good pull of air through front of rad, dont go by the air blowing over motor.

3, Flex fans suck, most are to flimsy, air FLOW is the key. If it dont over heat while running at hiway speeds then you just found the problem,
get rid of it.
4, is your timing correct, no really, check it again and then check your damper and pointer. did the rubber in the damper slip, they do this.

try these, let use know

 

I recommend pressure testing your system. I know advance rents a kit that will test both the radiator and the cap.

My cap failed and $5 later I was fixed. The pressure seal was leaking allowing the system to boil.

 

No joke about the difficulty!

Thanks for the super fast response Tom.

I am currently using a 180 t-stat. The fan is installed about halfway through the shroud like you said but it is difficult for me to feel air pulled through from the front. I just read some other threads and a common theme seems to be closing gaps between the shroud and the core. Do you agree? I haven't got it up to speed on the highway yet and I believe my ignition timing is right. 12@700 and approx 34@3000 w/o VA. I have a brand new harmonic balancer. What are your thoughts on the three row brass radiator? I have read a couple times they are barely adequate for even the stock set up. I am considering a 4 row aluminum radiator upgrade but don't want to if I don't have to.

 

Use your Ir gun to test the temp at the rad inlet and outlet. You should have approx 30°F difference.

Stock 3 core 77 rad is very adequate with the stock 7 blade fan and HD clutch, and the shroud fits well, but less leakage is always better.

Are you using a pressure balanced Tstat?

 

I'll check the in and out temps and the t-tsat is from Mr Gasket 180*. I have to wait till Saturday to do this. Today is my son's 13 b-day party and my wife gave me a chore list long enough there will be no vette time. My thought is: if the temp difference is to low, I still don't know if it is the air flow or radiator. And if the temp difference is ok, then what? Remember, I'm getting climbing temps at idle. It shouldn't climb this fast even with a substandard fan or radiator don't you think?

Thanks to everyone taking the time to give me these solutions. I'm learning a lot here.

 

After completing the rebuild, did you leave the radiator cap off when you first fired up the engine? If not, you may just have a big air pocket trapped in the system. From a cold-start, remove the radiator cap and fire the engine. Allow it to warm up to where the thermostat opens. You should be able to see coolant flowing at that point. If you have an air pocket in the system, as the thermostat opens, the coolant level in the radiator should start to lower. If so, refill to proper level, then reinstall the radiator cap. Hope that is all that is wrong.

 

Didn't notice you had a new rad.
About the only things it could be from your description is the fan air flow, tstat, ported vacuum, too lean a carb setting, vacuum leak, air pocket or exhaust leak into coolant. sometimes air pockets can be tough to get rid of.
The Mr Gasket tstats are known for giving intermittent performance.
You may want to try knocking the guts out of an old tstat and temporarily just using the frame as a restrictor to eliminate it.
Flex fans vary a lot, I used to use a 7 blade stainless one that put out far more than a stock setup, but some don't flow much air at all.
You won't find a 4 row alum rad, best you can get is a 1-1/4" 2 row, it will help a lot, but that shouldn't be your problem anyway.
For reference, my 77 with a slight cam in S Florida at 95° ambient, stock brass rad, stock 7 blade clutch fan, 180° R Shaw tstat, NO FOAM AROUND RAD, would stay rock solid at 180° both sitting in traffic or cruising at 3500rpm.

 

Did you buy the correct direction of flex fan ?
Try tricking water down the front side of the radiator to see if the temp will come down ,that's almost equivalent to increased air flow.

 

Your engine should be able to stablize with a 180 degree T-Stat . If not then you need to look at several key areas. Its the small details that makes or breaks a good stock vette cooling system unless you add electric cooling fan and other gagets to overcome the lack of everything else .

I had a many C3's and all would cool fine if the entire deal was there. There is a good 7 blade GM fan that came stock like on my 74 454 that moves alot of air . They are fairly easy to locate , I think Paragon sells them new. ANother Item you need is KNOWN good or new Fan clutch. I found an NOS one years ago. This helped the 454 alot. BTW: The 73-74 Z28's 350 engine used a really good HD GM flex fan that moves alot of air. Don't know if it will fit in the corvette for sure ?. I have an extra one in the attic.

You need the stock shrould and all the foam , gasket , seals , ect , ect.....this is where most vettes fail. Dr Rebuild has all these small items , you want everyone .

My 74 454 and some Latter vettes (79 L82 4spd) used "stock" an extra rubber lip rivited to the plastic spoiler extension. This added another 3-4 inchs of "SCOOP" to gather up additional air. It would be a welcome item on most C3 vettes that need the cooling increased . I think Dr Rebuild has sold out of these last time I checked , but you may be able to fashion a homemade one and rivit it on. Not a big deal.

IF my 74 BB can sit in the 90-95 degree /humity in the 80-90% and idle around town and not exceed 200 then your can can surely be made to do so. Just go down the list , eliminate as much as you can , and add the correct items.

 

I think this is really important. My 76 had a leak in a hose and by the time I got it home I knew I had to add more after fixing the leak which really just needed tightening. So, I added it to the coolant overflow storage thing. Next morning, storage empty so it sucked it back into the radiator. i thought I was cool then so drove it. Went well above 200 almost immediately but I was close to home and returned, garaged it and let it cool. As soon as cool I opened the radiator cap this time and was surprised that I couldn't even see any fluid! I had lost more via spray than I thought. The air that was in the system was almost fatal as pushing air in it instead of water doesn't do jack Shxxx to cool the engine. Filled it and then the reservoir properly, put the cap on, now runs as it is supposed to. it made a huge difference! HUGE.

 

Thanks to everyone for the advice. I haven't been able to try anything yet due to other important life stuff, But I'm looking forward to trying some remedies this weekend.

 

I had solved this problem a couple months ago but thought it would be good to follow up on this thread. I don't know if it is any one of the following but the new radiator seemed to make the biggest difference.

1. New 4 row aluminum radiator from Champion. A little tricky to install but not horrible. A little customizing the rubber mounts and it fits OK! I was going for 3 row but the vendor was out and upgraded to a 4 to keep the sale. I said OK!

2. New shroud seals. I new this could be an issue but I had make shift seals it before when trouble shooting with very little improvement.

3. New lower front spoiler. My old one was always there but had a crack in it. At highway speeds the crack may have separated and not functioned properly.

At idle or highway on hot Florida days it is cool as a cucumber. A 185* cucumber.