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Author Topic: Big Block heat problems HELP  (Read 4912 times)
396bud
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« on: September 04, 2007, 08:24:02 PM »

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 times 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.
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mark_sanders@bellsouth.net
396 RS SS RED 1968 Just like when I was 18 only 10 times the price
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maroman
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« Reply #1 on: September 04, 2007, 08:38:39 PM »

Have you used an infrared on the radiator. I know 2 differant radiators and still overheating SHOULD be soemthing else. Have you removed the condensor? Timing OK? Try one thing at a time.
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Doug  '67 RS/SS 396 auto I know the car since new
396bud
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« Reply #2 on: September 04, 2007, 08:58:54 PM »

I have not checked with infared but will do that soon. I have a friend that has one he will let me use. I promise that with 2 gages being used it really is hot. So hot that whe turned off it becomes hard to start. It is running electronic distributor and had that in it before the changes were made, so no condensor. The timing has been set 3 or 4 times now, trying everything from the book setting to higher and lower. Seems to make no diferance except in the starting. When timing it off the engine is harder to start.

THANKS for the help. Any more ideas??? THANKS MARK
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tom
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« Reply #3 on: September 05, 2007, 07:58:57 AM »

I think the condenser mentioned above would be the A/C condenser in  front of the new radiator, not the ignition condenser. I presume you installed new hoses with the new radiator. Is it possible there is a kink, collapse, or some other restriction related to the hoses? Have you tried pulling the thermostat completely?

Good luck,

Tom
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JohnZ
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« Reply #4 on: September 05, 2007, 10:07:59 AM »

Do you have a proper fan shroud? Does the outside diameter of the fan blades match the diameter of the rear of the shroud, with the ends of the blades half-in/half-out of the shroud? Is the shroud sealed to the back of the radiator?

Is your vacuum advance connected and operating? Is it connected to a full manifold vacuum source?

Your symptoms indicate that you have an adequate radiator, but inadequate airflow through it, both in traffic and at highway speed. Lack of a proper shroud would be a cause in traffic, and adding a fan in front of the A/C condenser is causing a major airflow blockage through the radiator behind it.
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rich69rs
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« Reply #5 on: September 05, 2007, 01:05:09 PM »

Be sure that you have your distributor vacuum advance connected and that it is operating properly.  Double check your total timing at idle with the vacuum advance connected.  If you don't have enough vacuum advance at idle, or if the vacuum advance is not working, the timing will be more retarded than it should be which will increase the engine heat load to the cooling system at idle with a potential result being running hot at idle.

Following is a reasonable approach:

10 - 12 degrees of initial (mechanical) timing.

At idle, 12 - 15 degrees of vacuum advance from a vacuum can that is fully deployed at idle with normal engine intake manifold vacuum, resulting in total timing (sum of initial and vacuum) of 22 - 27 degrees at idle.  The vacuum source should be full manifold vacuum, instead of the ported vacuum source at the carburetor. 

At cruise, 20 - 24 degrees of centrifugal advance built into the distributor, resulting in total timing  (sum of initial and centrifugal) of 30 - 36 degrees, with all of the centrifugal advance in by 2800 - 3000 rpm.
« Last Edit: September 05, 2007, 01:17:17 PM by rich69rs » Logged

Richard Thomas
1969 RS
396bud
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« Reply #6 on: September 05, 2007, 06:16:35 PM »

OK.......I will get to work on getting some answers and checking a few things ....THANK YOU and keep the ideas coming .. Mark
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396bud
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« Reply #7 on: September 05, 2007, 08:59:04 PM »

I do not understand the timing thing. The book says that timing should be set at 14 deg. Remove and plug the vacuum line and check at idle. I have done this and then put the vacuum line back on. The timing light then shows the timing mark way off of the timing tab, so I have no idea of the degres. How do I check this total timing etc? The car starts good, runs strong etc...no pinging and I run regular gas. (low compression engine)

Thanks again Mark
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rich69rs
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« Reply #8 on: September 06, 2007, 03:30:38 PM »

You need a timing light with an "advance" feature, usually found as a dial at the back of the timing light and graduated in degrees from 0 to maybe 60.  As you have noted, when you connect the vacuum source to your distributor, at idle, the timing mark moves off of the timing tab.  With the advance dial on the timing light, you turn the dial until you bring the timing mark on the balancer back to 0 on the timing tab.  You can check initial and total timing by simply turning the dial in order to bring the timing mark back to 0 on the timing tab and reading the timing directly from the scale on the timing light. 

If you want to check the total timing at idle (mechanical + vacuum);  hook up the vacuum source to the distributor and turn the dial on the timing light until the timing mark is in line with 0 on the timing tab.  For example, you have 14 degrees of mechanical timing.  If you checked the total timing at idle and from the timing light scale you read 29 degrees, then you would have an additional 15 degrees of vacuum advance at idle (14 + 15 = 29). 

A must have feature in order to check vacuum or centrifugal advance / total timing.

They come in many variations and price ranges.  You can get a decent one from Sears (Craftsman) for $70, or you can pay over $400 if you want Snap On.  Following is the Craftsaman variant: http://www.sears.com/shc/s/p_10153_12605_00921023000P?vName=Automotive&keyword=timing+light

Also, the following is a very good write up that JohnZ posted previously:

....... but it helps to understand the logic behind it; I explained the logic in some detail in an article I wrote in the October/November 2003 issue of "Corvette Enthusiast" magazine (I'm the Technical Editor of that publication), and the cut-and-paste below is a more concise version that explains ignition timing and advance systems and how they work together - kinda long, but you can't explain these systems in layman's terms in one paragraph:

                                            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.
« Last Edit: September 06, 2007, 04:07:43 PM by rich69rs » Logged

Richard Thomas
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396bud
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« Reply #9 on: September 06, 2007, 07:13:45 PM »

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
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