When I drive around the back roads and side streets my temp is about 195. When I drive on the highway the temp goes up to 220+. I have a 71 455 in my 69. I have all the stock stuff. On the back roads my rpm's are 2500 or less, when i'm on the highway it's 3000 or more rpm's. Any thoughts on why the temps will be higher on the highway?

From my experience if traveling at highway speeds makes the car run hot, it is NOT an air flow problem, it's a water flow problem. And then the opposite would hold true if the car runs hot sitting still, this would be an air flow problem not a water flow problem.

So in your case, it's a water pump issue, thermostat issue etc. Something with water flow, too fast, too slow etc. Are you using the correct pulley set up for THAT engine?

could be several things..
1)Since its 455
, do you have all the 400 fillers?
2) radiator cleaned out?
might need a 3 or 4 core aluminum rad...since its a bigger engine than stock
3) cab may be set too lean

could be many other items, but I`d start there

I do have the 400 fillers. New radiator and water pump.
I think my pullies are all from a 69. Not sure.
Should the upper hose have a spring in it to keep it from colasping? Mine does not.

No spring in the top hose, but yes in the bottom.

I think it is an airfow problem due to poor aerodynamics - not enough air going through the radiator. Going around instead. So you're not getting the cooling that you think you should be getting at high speeds, while the engine is revving high.

If you going down the road at hiway speed, wouldn't it be safe to say that there would be enough air moving through the rad.? Especially since he did say that he does have all the fillers in place etc.

Betcha he has a stock 3 row radiator and it's just a matter of it being inadequate for the 455 cube. And the faster you go the more heat you have to disipate.

I agree with EarlyBird, there should be enough air for cooling. But if the heat does not get to the rad then it cannot cool it.
Do you know if the thermostat is working properly? You can test it in boiling water to see if it opens at the right temp.

Do you flush the system?

We rented a car once and it overheated. My Dad checked under the hood found the fan was in backwards (blowing into rad).

Yeah, you'd think you would have plenty of air going through the rad. But you'd also think you had plenty of air going into the scoops (if open) which has been proven to not be the case.

What about the masticated filler pieces that direct air flow though the radiator? I found they helped reduce the operating temp of my 400.

If he's running at 195 around town 2500 and below, then he goes on the highway and temps rise to around 220, it stands to reason the system is working but cannot transfer the heat out of the radiator efficiently enough. The T-stat will be open all the way on the freeway, plenty of air flow and the pump will be spinning up fast enough to circulate....draw you own conclusions, I'm sticking with an underperforming radiator. In any case we need more info from David to make a more accurate diagnosis.

Actually, they found out later the scoops were, at times, drawing air out instead of in. That's why the 69 and later RA hoods have the scoop at the front.

Ummmm ... no.

The scoops are in the boundary layer (even on '69 cars - including the Trans Am) and don't actually "ram" air into the engine. At best, they allow COLD air into the engine.

If the engine is running, there's a negative pressure gradient at the mouth of the scoop that would absolutely prevent the air from being "sucked out" at ANY speed below supersonic.

Not until 1970 were the scoops moved out of the boundary layer on the 2nd get Firebird. The GTO had "forward" scoops which were still in the boundary layer until the NACA ducts of the 1973 and the shaker used in 1974.

The orignal '70 T/A shaker was intended to be mounted on a dual quad intake with the opening facing forward.

Do you have anything obstructing the rad like a transmission cooler or A/C unit?

What size is your new rad? Stock, thicker than stock?
After market Aluminum?

Are you bypassing the heater core? Are supply and return lines attached to the correct ports on the engine? Your supposed to have the supply and return lines close to the same length.

When engine is hot is the top rad hose very hot as well?

What kind of fan? Stock 4p, clutch or flex fan?

I can't say enough about the flex fan. We do not have near the hot days you guys get but after I rebuilt my engine it ran real hot, all the time. Gas line would peculate and you could fry an egg on any piece of the engine compartment. Put the flex fan and instant cooooool running engine!

Hey guys,
Thanks for the replies.
I don't have the masicated fillers on the sides. The fan is a stock fan with a clutch.The rad is a replacement 3 row copper.
Heater is not bypassed and the thermostate is working properly.
Nothing blocking the radiator. The shroud is aftermarket and the fan dosent fit so good in the opening.
I can drive around all day on the side roads and the temp stays at 195 but I hit the highway and up it goes. As soon as I come off the highway the temps go down. The car is a 4 speed with 3:73 or higher rearend gears. About 3500 rpm's at 65 mph.

Could be engine calibration. Improper air/fuel ratio and/or ignition timing at highway cruise speeds could be causing abnormally high combustion temperatures.

those were missing on mine when I bought it...installing them reduced my temps about 10F...do you have the lower baffle? just the X fillers is not enough..thats only 1/3 of the fillers needed.

Yup got the lower baffle.

did you check your water pump impeller clearance to divider plate before installing it? It sounds like you are just not pumping enough water through the rad.

Some advice Vikki gave me when I was looking at buying a lower filler from her and explained I was having a similar problem:

If your car gets hotter with speed, suspect the lower radiator hose collapsing, water pump divider plates with excessive clearance or holes, stamped steel water pump impeller, ribbed flex radiator hose, bad fan clutch if clutch fan, or flex fan with improper relation to shroud, or clogged radiator cores or undersize radiator.

With the engine warm, squeeze the lower radiator hose. If you can pinch the two walls together, the hose is weak. Try to find a spring to insert in the hose to permanently fix the problem. These are available from aftermarket companies.

FWIW

David
Is this a new or existing problem? I might explore another route.
Are you running ported or manifold vacuum to the distributor. If you are running ported you may find switching to manifold vac solves the problem.

Some interesting reading I found on another site.
This is a great article!!!!I had my vacuum advance hooked up to the ported vacuum port after reading this article I hooked it up to full manifold vacuum adjusted the idle rpm.The car has so much more power now.



As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense, and as a result, a lot of folks are under the misunderstanding that vacuum advance somehow compromises performance. Nothing could be further from the truth. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. I have this as a Word document if anyone wants it sent to them - I've cut-and-pasted it here; it's long, but hopefully it's also informative.

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.
__________________

hope this helps

Thanks so much for that information Tony. I have attached it as a PDF file for anyone who would like to download and print it.

<timing and vacuum advance is one of my favorite subjects,>

It's one of mine too, but what would know as for p's and q's?

?????????????

a BIG THANKS for posting this ! Great explaination on how the vacuum advance works, and in words I can understand. Please keep up the good work on supplying such superb information !
Tom

I can't recall for certain but I think they were starting with the ported vacuum in 71. I noticed cooler temps all across the board when I switched mine. Except of course when stretching out the wings a bit!

Well after reading the above posts I went out to my car and switched the vacuum advance from ported to manifold, my engine dieseled when I shut down. I had 8 deg btdc initial advance and idles at 600 rpm. When I switched it back to ported the dieseling stopped.

Are you setting your base timing with or without vacuum hooked up. Go for 12 degrees as your next starting point with no vac advance and let us know.

Before playing with initial advance, you need to find out what your centrifugal is giving. This way, you won't be exceeding to a point of detonation at heavy loads.

The closed chamber heads ('67 and earlier) usually tolerate as much as 42° total, and the open chamber heads 36° total. And you don't want max timing coming in before 2600rpm. Make sure you do a sweep up to 5000rpm in case the weights are sticking. This should be checked without vacuum advance of course.

So if you find at 8° initial, you're already ending up at the 36° total, and you want more intial, then you need to reduce the centrifugal before you start actually driving the car.

Also, simply hooking the vacuum to full manifold may happen to work for some, but that's quite hit or miss without an adjustable vacuum can. That's not to say it wouldn't help, it's just that you might be getting too much from that particular vacuum can.

I like to set the timing by finding out how much initial the engine can handle on a hot restart (vacuum disconnected).

Then, set the total timing with 4° less than optimal for the heads, and walk it in for the best acceleration and without detonation (vacuum still disconnected).

To figure out how much vacuum to add for cruise, requires driving to see if the engine surges at constant speed, or detonates on throttle tip-ins.

As to whether the full vs. ported, depends on what your vacuum gage reads, based on initial without vacuum. If you're getting 16" in-hg or more you're probably better off with ported. If it's less, I'd try connecting to full vacuum and adjust the can until it produces the highest vacuum reading but doesn't diesel. I've seen vacuum readings improve by as much as 8 in-hg using full (with the carburetor re-adjusted to match) depending on compression ratio and camshaft overlap.

Keep in mind, switching to full vac. also means you'll need to re-adjust your idle mixture (it tends to become more rich, so you need to lean it out) and idle speed (it will increase due to the more efficient combustion, so it needs to be reduced). It will also smooth out the idle more than it was.

It's a 68 428 with 69 #48 heads, HEI, Edelbrock 800 cfm carb. Idle-550rpm.
Checked the vacuum: 500-9; 750-13; 1000-15; 2000 & up-18.
Timing no vacuum advance: 500-6; 1000-9; 1500-14; 2000-20; 2500 & up-24.
Timing vacuum advance at manifold pressure: 500-8; 1000-10; 1500-41; 2000-44; 2500 & up-48. Didn't check with the VA ported.
Took the car for a spin with the VA at manifold and it seemed to fluctuate at cruise and pop the exhaust going down hill no throttle. It stopped the pipes from rapping when I changed gears which it did with the VA ported.
Diesels with VA at manifold not when ported. Adjusted mixture for both ported and not. IF it runs on at 8deg. I'm reluctant to try 12.

do you have a large cam? Based on your vacuum I will assume so. It seems strange 2 degrees of timing would cause the engine to run on. I am not sure about the 428's but I would expect more mechanical than 24 total. It seems the distibutor should make more than 18 degrees mechanical. I may be wrong but I think there is some power to be found there. As for your vac advance you may want to find one that comes in at as close to 9" of vacuum. I would also try to limit it to around 12 degrees initially, and adjust from there. Is there any ping on light acceleration. Ping at wot indicates too much mechanical, and ping at light throttle would be too much vacuum advance. Your fluctuation is either the vac advance not haing enough vacuum to opereate or and most likely too much vac advance. I would let a few others chime in, because I can't understand the engine dieseling at such low rpm and timing? Does the engine run hot? Are you running hot plugs?

71? After 35 years of tinkering with cars, I always assumed ported vacuum was the standard connection since the sixties or earlier. Late 60's Chevys were my first introduction to cars and it always seemed that ported vacuum was the factory connection.

This is getting interesting...

I can't date it for sure, but I remember always having a few golf tees in my box to plug the advance hose when adjusting timing. I also remember the timing retarding when doing so. If they were hooked to ported vacuum this would not happen. Should be no ported vacuum at idle.

Anyhow I was just looking to see if we could cool him down a few degrees, thought it was at least worth a look?

I apologize to David for straying from his overheating topic. Perhaps we should have started another thread?

I don't know what the cam is or what the Distributor came out of, and what if anything has been done to it. I suppose a good place to start would be to take the dist. out and check the mechanical advance and replace the vacuum can.

Hey guys,
Thanks for all the replies. Tony thanks for the VA write-up.
I checked and I am connected to manifold vacuum on my Edlebrock 750 carb with a an Edlebrock proformer manifold. I do have a steel empeller on my water pump and I did reduce the gap between the empeller and plate. My hoses look good.

How do I check total timing? How do I check when it comes in?
I do have some knocking/detonation under load. My distributer is a GM HEI. I set my initial timing to 6-8 deg. before with the vacuum hose plugged.

I have a new fan clutch but I could try running without it.

Thanks for all the help.

David

Dave I don't know the history of your engine or car. You mentioned you have a stock clutch fan in an earlier post. Does it seem to work? I can often hear mine turn on in my blazer. It can't hurt to change it if you are suspicious of the one in the car.

I am going to assume you have a ping at w o t. If every thing else is corect it could indicate too much mechanical advance. It also could be a lean or hot condition.

Lets start at the begining. I first would eliminate the posibilty of vacuum leaks. I usually spray carb cleaner along the base of the carb, the base of the intake, around the brake booster, any vacuum line or connection a leak may be possible. Many times the line at the vacuum modulator on a/t cars will show the leak. When the leak is found your rpm will change. Small leaks it goes up larger leaks it falls. Keep in mind carb cleaner is flamable, and there are other safer ways to check for leaks. If you find a leak repair it retune and test ride.

The rubber seals on the sides of the radiator were mentioned earlier, they are available on E-bay fairly cheap. You mentioned it runs cool on backroads, and warm on the highway. In traffic you may have less airflow, with clean air on the backroads. A couple pieces of tar paper and duct tape would survive a test ride. Just dont tell anyone it was my idea.

I like a good quality 160 degree stat.

You mentioned an aftermarket shroud with poor fan fitment, I would do a lttle research on that.

Mechanical advance can be measured either with a timing light with an advance dial, or by degree tape on the harmonic balancer. I think this is checked around 2500 or 3000 rpm with the advance can disconnected. Check a book.

Vacuum advance can be checked at idle by connecting the vacuum line. Ad the two together and that will be your total advance at cruising speed (no load).

Ping may be caused by the advance coming in too early also. You can get a curve kit and try a heavier spring. You may even find you have too much mechanical and not enough vacuum advance.

If you would like to talk pm me your E-mail I can send you my phone nuber.

Here are some filler panels I've not seen before. That might help with your over heating issues.

http://www.firebirdcentral.com/product_p/she-1722.htm

seems to me that IF you have the regular lower baffle and the masticated fillers this wouldnt be necessary...plus its not "factory".....