jfy39

With all the experience and knowledge out there I'm sure that someone must have seen this problem and has a cure ( I hope).

My '66 BB will idle "all day" with no problem and drive at 55/60 with respectable temperature but when I get to 70 on the expressway, the temperatre starts to climb to the point that I slowed down to get it to stabilize. I never got to over temp or boiling but it seemed as though it was headed that way. I have changed the sending unit and that didn't change anything and am now trying to increase the timing to be sure I am not heating up from running retarded. I am currently at about 50 degrees total at about 2500 rpm in the garage. I haven't yet run an expressway test. That's next when the weather clears up.

Any help will be greatly appreciated.

thanks, John

kellsdad

While it is true that improperly retarded timing can cause some overheating problems, I wouldn't start solving an overheating problem by arbitrarily advancing the timing. I suggest you read up on how to set your timing and reset it to the correct setting. ... As for the overheat condition - is this something new? Have you changed anything (other than the timing) recently? How old are your cooling system components?

If you have old cooling system components and the problem has been coming on slowly, it could be a clogged radiator.

wmf62

hmmm, it sounds like the airflow through the radiator is diminished the faster you go.... does your radiator have real close together fins between the tubes? if so, it will only pass so much air, no matter how fast you go; it effectively becomes a 'wall' at higher air speeds.

or. maybe there is a lot of 'stuff' in between the fins that is blocking some air flow; making it more of a wall.....

do you have all the rubber 'seals/flaps' in place around the radiator? if they're missing, a lot of air can bypass the radiator. i saw a 64 the other day that had the 'flap' at the bottom of the fan shroud-to-the-front crossmember missing and the fan was sucking air from under the car and not through the radiator; they installed the missing seal and the air flow through the radiator improved noticeably. i would assume air flow would bypass the radiator this way going down the road too....
Bill

EVERGREEN

Lower radiator hose collapsing?
Jerry

kellsdad

I have to disagree. It is unlikely the airflow is diminished with increased speed. It is more likely that corrosion and dirt within the radiator is limiting the amount of coolant that can flow through it. As the car goes faster, the engine generates more heat that has to be dissipated by the radiator. At idle and low speeds, a clogged radiator may be able to provide sufficient cooling, but as the engine produces more heat at higher speeds, the coolant temperature would rise.

jfy39

Just finished a complete restoration including having the radiator tuned up at a radiator shop. I don't know just what that amounts to but I assumed he cooked, cleaned and painted it. Is there any way to tell. By the way the timing is only a little advanced from specs and I will need to bring it back as I'm now getting a very light spark knock.

I just ran anexpressway test and it still climbed but seemed to stay in a safe zone. I'm not sure if it stabilized though. I went about 15 miles.

John

wmf62

ahhhh, but it can. might be unlikely that it's causing his problem, but it can... try driving down I-10 and hold a window screen up over your windshield and see how difficult it is at higher speeds....
Bill

piper

Run that BB It is not going to stay at 180 . All people with BB worry about the temp. (I did when I had one ,but it never over heated and mine did the same thing as yours But never got over 220

magicv8

IMO that factory brass BB rad can't hold a 300hp 350cid SB at 180F above 75mph. IMO if you want 180F all the time you will need an aluminum rad. I am told (by a rad guru on the forum) that the SB rad has more capacity than the brass BB unit.

If you have the flat sheet metal shields screwed to the frame and the floor, try removing them to improve high speed airflow. The racing cars resorted to huge hood grilles to get rid of the heat. Street cars don't have that option, but a big electric fan will do the trick.

jfy39

Thanks for all the input. I will try to get a correct temp reader to see what the actual temp is. I may be worried for nothing -- hope so.

the idea of removing the flat plates from the bottom of the engine compartment also sounds like a good idea. I'll see what happens.

Thanks again for the ideas.

macdarren

I posted about something simlar several months back, My problem years ago was almost the same as yours...turned out it was of all dumb things the suspension....the car lifted it's nose after a certain speed and air flow droped enough that temps would climb like crazy. Having a 4:11 rear didn't help either....mine was a small block so lift might have been more a problem.

Just a thought
Darren

rongold

Get a DeWitt aluminum radiator. I just installed one in my 67 435 HP 2 weeks ago. It hasn't gone over 180 since.

RON

0Tom@Dewitt

Yes it will be hard to hold it and that's because of the huge pressure the air flow creates. When we had our radiators tested, I found that the lab uses pressure drop across the radiator to calculate CFM. The higher the pressure, the higher the cfm rating. You're right about the higher pressure but wrong about the cfm. Higher speeds will produce higher cfm's and air flow is not the problem here.
As mentioned, you need to check that lower hose...if it does not have the internal spring you could suck it closed at high rpm.
MagicV8 is correct too, the BB copper unit is marginal. That's why c/b radiators grew in size in the later years. Check the sender, check the hose, and if you find nothing wrong, then an aluminum radiator might be the solution.

magicv8

If you want a hose with a spring in it, get some stainless wire (I suppose squeezing the lower hose will be added to flight judging ) because the current replacement hoses (even GM) do not have them. They are now considered unnecessary, due to improved strength of materials.

jfy39

Thanks again for the input. The lower radiator hose is new and does contain the spring. I will, however, make sure it is routed correctly and does not have a kink in it..Next step, check the actual temp when the weather becomes more agreeable.

GaryS

I couldn't agree more with this statement. I can tell you, from personal experience with my own 66 L79, that my car's symptoms were identical to yours. I could drive all day long in traffic and at lower speeds on the roads around town. However, once on the open highway the temps would always climb. I did everything: new temp sender, cleaned contacts on the temp gauge, checked for collapsing hoses, checked timing, flushed system, tried to burp any remaining air, etc, etc. I screwed around with these symptoms for five years. I finally bit the bullet and bought a repro DeWitts aluminum radiator and FINALLY could drive my car anywhere, anytime, and at any speed. Fwiw, my radiator even flow tested well. Unfortunately, no one could tell me what a normal flow rate was.

I still have my original, non-leaking radiator and I would love to cut it open to see how much crud is at the bottom. I now have a IR gun that would allow me to shoot the radiator to get the temperature but that car is long gone.

Gary

Birdball

hold on hold on with the wild big block rumors!! My .030 over 11:1 427 will idle forever in the Detroit summer heat and Drive 80mph down the freeway without even getting a needle width above the 180 mark. The factory radiator and cooling system works fine as long as everything is in proper tune and good shape.

The first thing to do is re set the timing properly, with the vacuum advance blocked off and 36degrees total timing. Then plug the advance into the full time vacuum port so that you maintain lots of advance under part throttle cruising as well as idle conditions.

I suspect you have
1) a cooky thermostat that is sticking
2) or an aftermarket "High flow" thermostat and or water pump
3) or a collapsing lower radiator hose
4) or an air pocket that needs to be bled out
5) Heating up under increased speed lots of times means a radiator full of junk or corroded shut...
6) combo of both

keep us updated on your progress!
Matt

jfy39

I just ran a test on the expressway at 70 mph and got about 218 degrees after about 15 miles at 70. The lower hose is new and is not kinked and does contain a spring, the radiator was cleaned and flkow checked (???) and is supposedly OK (who knows). I have put in a new thermostat sometime back and it was off the shelf from my local pares dealer. Is there something different about a Corvette thermostat?

I don't think that the 218 degree temp will be harmfull but if I'm wrong let me know.

I have tried to maintain originality as much as possible so Idon't want to use an aluminum radiator unless absolutely necessary. Also I don't plan on running it at the local dragstrip.

I also changed the water pump several years ago but think it was a correct replacement (??) I don't know how to tell though.

Again, all this input is helpful, thanks.

JKohn

rongold

===================================
Either find someone with an IR temperature gun, or get one for yourself. I had a friend stop over at my shop with his 63 340 HP convertible the other day. He got a "correct" temp sending unit from a well known vendor, and installed it a few weeks ago, because his old one seemed to be reading too high. It was supposed to be correctly calibrated internally, but it came with a series resistor. When he got to my shop, his gauge was right on the 220 degree mark. I felt his upper hose--it was hot, but nowhere near 220 degrees. After doing auto repairs for 33 years, you get to know what 220 degrees feels like.

I said to him, this feels no higher than 170. Sure enough, when I shot it with my Raytek ST-25 IR gun, the upper hose read 157 degrees. The lower hose was about 146, his expansion tank was about 162, and his radiator core was about 158. Your problem might also be a mis-calibrated sending unit. Shoot it with a gun.

jfy39

Ron,

Thanks, I will find a gun somewhere and get a reading. I also feel like the temperature is not as hot as 220 degrees.

By the way, doesn't any air in the system automatically bleed out after driving for a while? I have put a few hundred miles on the car since filling the radiator. How would one bleed the air out if it is still there?

Also, how do I know if the thermostat is "high flow" and if it is incorrect?

I can boil it on the stove but what do I lood for to know if there is something wrong?

Thanks again in advance.

John