Trying to cool my 59 on hot summer days

[Mark E.]

Re: Trying to cool my 59 on hot summer days

@400 - 1*
@1300 - 7.5*
@1850 - 10.5* - 11* +16" = 17.5* +18" = 19*

On car at idle:
No vac = 4*
w/vac = 22*

Mark, at 1850rpm the centrifugal advance was 10.5*-11*. When 16" of vacuum is added the advance goes to 17.5* etc.

Duke was poking at this in his post about engine vs. distributor RPM and degrees...

Most GM V8 engines run well at wide open throttle with a total timing advance of 36 - 40 ENGINE degrees at 2600 - 3700 ENGINE RPM. (This is WOT = No vacuum advance.) You can check this with a dial back timing light, or a regular timing light if the harmonic balancer is marked.

Your data from the Sun machine may be DISTRIBUTOR or ENGINE RPM and degrees. Given your numbers, I suspect they are DISTRIBUTOR data:

11 degrees @ 1850 RPM at the DISTRIBUTOR is 22 ENGINE degrees @ 3700 ENGINE RPM.

To achieve 36-40 degrees total requires 14-18 degrees initial (again not counting VAC), which may be too high for your engine.

If you have VAC working at idle, this limited advance curve probably would not cause overheating at idle, but may impact overall performance and fuel consumption.

Once you get centrifugal and initial timing dialed in, then you can choose a proper VAC and sort out total advance at idle and cruise.

Duke and others have some great threads and papers with more details you can find with a search.

[Duke W.]

Re: Trying to cool my 59 on hot summer days

What Mark said. The centrifugal is short of AMA specs, but is likely not the full cause of your hot running at idle and low speed traffic, but you are leaving mid to upper rev range torque and power on the table.

The ...163 is a boat anchor and does not meet the Two-Inch Rule for even a base engines. The correct OE and functional replacement is a B22 (NAPA VC1802 or equivalent in another brand) if a manual trans and B26 (NAPA VC1765 if a Powerglide.) The B22 start at 8" and adds 16 crank degrees at 15", and the B26 starts at 6" and provided 16 at 12" See the following thread about a 1965 VAC TSB:

https://www.forums.ncrs.org/showthre...um-Advance-TSB

Your total idle advance is basically okay - in the range of 22-26 for a base engine, however the centrifugal is short, especially with only 4 initial. My recommendation is to correct the centrifugal and set initial timing to achieve about 38 total WOT advance which would be about 8 initial. Add that to the 16 vacuum and total idle advance should be about 24. Too little total idle advance is more likely to cause hot running than too much.

Given the new radiator and proper coolant mix, low speed airflow may be an issue, so a fan with greater CFM should help. With your 15 psi cat and a 50/50 glycol/water mix the boilover temperature is 265F. It would be a good idea to test your pressure cap. Most parts stores have pressure testers at the counter, so it's easy to check.

In hot weather idling/low speed traffic operation, elevated coolant temperatures are normal, and with your setup I would not worry unless the temp gets over 230. With a 180 ...stat I consider the normal operating temperature range to be 180-230. The thermostat only establishes the minimum operating temp and is not full open until about 20 degrees above the initial opening temp that's usually stamped on the stat. Thermostat is easily tested on the stove with a pan of water and a meat thermometer.

Another possibility is that the water pump may not have adequate flow at low revs. There were many different impellers used on these pumps over the years, and in general idle coolant flow is greater than necessary in order to provide good flow to the heater core in cold weather. However I have seen "rebuilt" water pumps with severely corroded impellers that severely compromised coolant flow.

My recommendation is that you get the spark advance map squared away first, verify that the thermostat is performing to sped, then either install a higher CFM fan or remove the water pump, take off the back cover, and determine if the impeller is correct for you engine and in good condition.

One other note: Before you(or anyone else) accept delivery of either a "reproduction" VAC or a generic OE replacement always use a vacuum pump to verify that it starts/stops +/ 1" Hg of spec and verify that it provides advance within +/- one degree of spec after it's installed. There are "reproduction" VACs out there that are stamped with a OE numbers that are no where near OE spec for that OE number.

Also, some original VACs were poorly chosen by GM. Examples include '65 L-78 and '63 L-76 (don't pass the Two-Inch Rule) and L-79. (The OE 8" 236 16 is more aggressive than necessary, and a better choice would be the 12" 355 16, which is the current B26 OE replacement.)

Duke

[Pat H.]

Re: Trying to cool my 59 on hot summer days

I've had a similar problem with my 59 230 HP. I've checked everything except the rad cap which I thought was okay. It wasn't. I'm also wondering why Bob is using a #15 cap. The spec calls for a 7#cap. After much of last summer wrestling with the heating problem, I finally had the cap checked and It was bad. I had 2 other 7# caps which were also bad. They were all re-pop's. I did note that Duke mentioned the vacuum advance difference for a PG vs a standard. My car was originally a PG car, but I changed it to a 4 speed and used the NAPA B-22 advance and did not have a problem. Now that the car is restored and back to a PG, I think I'll purchase the B-26 Advance, and maybe that will cure things once an for all. I'm going to try and add the 60 fan spacer to move the fan closer to the rad. I haven't done it yet. I hope its not going to be an issue.

[Duke W.]

Re: Trying to cool my 59 on hot summer days

Running a 15 psi cap is a good idea for normal driving because it increases the boilover margin. Use the 7 psi "repro" for judging. Like a lot of repro parts that may look correct or close to correct, many do not perform to OE spec.

A base camshaft engine with manual trans idling in neutral @ 500 should pull about 18" Hg manifold vacuum, so the 15" B22 passes the Two-Inch Rule.

A base camshaft engine with PG should idle in Drive in the 450-500 range, but will pull less vacuum. That's why I recommend the 12" B26 for this configuration, but I'm not sure if it's correct.

I have been asking for YEARS, for someone to take a vacuum reading on a base engine/PG setup idling in Drive - vacuum in inches Hg @ idle speed in Drive (range of 450-600), but have never gotten a response, so I'm making the request again.

Duke

[Bob S.]

Re: Trying to cool my 59 on hot summer days

Duke,

Can you tell me what my timing should be at idle with vacuum? In looking at the ST-12, for the 1110946 distributor, full advance should be at 15-16" of Hg. Max. Dist. Advance should be 7.5*. Does this mean if the advance without vacuum is set to 4* then with vacuum of 15" the total advance should be 11.5*?

My car pulls 15" at idle (500rpm) but my total advance is 22*. This is a far cry from 11.5*. Would that much advance be my problem?

Thanks, - Sully

[Duke W.]

Re: Trying to cool my 59 on hot summer days

You need to know whether advance is specified in distributor or crankshaft degrees. It sounds like ST-12 is stating vacuum advance in distributor degrees, which are half crankshaft degrees, so maximum crankshaft advance should be about 15 at 15" Hg manifold vacuum.

So assuming that the centrifugal curve starts above idle speed, total idle advance should be 15 + 4 + 19. This is less than ideal for a base cam engine, which I like to see in the low to mid twenties.

It's also not clear to me what VAC you have installed - something about 163 and something is Xed out. In a previous post I stated that the 163 has no place on any production Corvette engine regardless of what the parts books say. A photo of the data stamped on the bracket would be good.

Another issue you may have is inadequate centrifugal advance. According to the distributor test data is only has 11.5 degrees, which is 23 at the crank. The ST-12 should specify the centrifugal advance start/stop points and maximum advance. It is also in the AMA specs. I suggest you post both the centrifugal and vacuum advance data so we have a reference point.

The "spark advance map" has three components - centrifugal which adds advance with increasing engine speed and vacuum advance that adds vacuum advance inverse to engine load, which means the lighter the load, the more advance. The final component is initial timing.

When working on these issues one should have the OE specs handy as a reference point. Then test with a dial back timing light and vacuum pump to determine the centrifugal curve and vacuum advance behavior, which is the start point and stop point and maximum advance. Over the decades many distributors have been modified, some for the better, but many for the worse.

So what you need to do now is determine on the car how much total centrifugal advance is available. Does 22-23 meet spec? Maybe the guy who tested it didn't rev the distributor high enough to achieve maximum. I don't know because I wasn't there, so you need to test it again on the car with a dial back timing light, and test the VAC with a dial back light and vacuum pump.

Total WOT advance is the sum of initial and full centrifugal and it should be in the range of 36-40 degrees. Detonation is the limiting factor on how high in this range you can go.

Total idle advance is the sum of initial and full vacuum assuming centrifugal does not start at or below idle speed and the VAC meets the Two-Inch Rule.

Once you determine the complete centrifugal advance curve and vacuum advance curve on the car, then it's just some arithmetic to pick an initial timing value.

Duke

[Bob S.]

Re: Trying to cool my 59 on hot summer days

Thanks Duke. I will head to the NAPA store in the morning to pick up the VC 1765. (There is a picture of my current VAC in one of my posts above.)

Your good explanation will give me some work to do. I will also get with the tech who ran my distributor to make sure we are all on the same page. When I get all of the information I will post it for your thoughts.

Thanks again, Sully

Sully

[Duke W.]

Re: Trying to cool my 59 on hot summer days

Does your car have Powerglide? If it's a manual trans the correct VAC is a 8/15" B22 (VC1802). The 6/12" B26 (VC1765) is for automatic transmissions for reasons I explained earlier in this thread.

I now see the photo and the installed VAC is certainly suspect. Where was it procured from?

For the third time I am asking you to post the centrifugal advance data from ST-12 or the AMA specs. You should check both to ensure they are the same. That way we can be pretty confident that the data is accurate. I think there is a problem with your centrifugal advance based on the measurements from the distributor test machine, and it needs to be compared to OE spec as a starting point.

Do you have a Mity-Vac? If so, take it to the store and test that the VAC begins to pull at 6 or 8" and is at the limit at either 12 or 15 depending on which one you need before you accept it. If you don't have a Mity-Vac maybe the store has one you can borrow.

Also check the start and stop points of the installed VAC.

Duke

[Bob S.]

Re: Trying to cool my 59 on hot summer days

Duke, My car is a Manual trans but I am only pulling 15" at 500rpm. With the Two-Inch Rule should I go with the B26 or maybe I need to check for vacuum leaks.

The VAC installed came with the car when I purchased it.

The centrifugal advance data from the ST-12 is as follows: Centrifugal Advance (Distributor Degrees and RPM)
Start .5*-2.5* @ 400 RPM

Intermediate 9.5*-11.5* @ 1300 RPM

Maximum 13*-15* @ 1850 RPM

Under Vacuum Control it says:

Inches of Hg. to Starts 7-9"

Inches of Hg. full advance 15-16"

Max Dist. Advance 7.5*

When run on the SUN machine my notes show the following centrifugal (I have not been able to talk to the person who did this yet to see if these are dist. degrees)

@ 400 - 1*
@1300 - 7.5*
@1850 - 10.5*-11*
I am not sure what he is saying here, but under the 1800 he has the following:
+ 16" = 17.5*
= 18" = 19*

I will try to get this answered.

[Bill L.]

Re: Trying to cool my 59 on hot summer days

I'm only going to address the flex fan issue. Many are led to believe the flex fan is the penultimate of fans. Not so!! Keep in mind a very important point "the flex fan flattens out as RPM goes up where it delivers miminal air flow". This fan works best at highway speeds with air velocity thru the radiator created by the forward momentum of the car. Now consider this example: a flex fan on a pickup pulling a heavy load up a grade. The pickup must be geared down to pull the load creating an impossible condition. Due to low truck speed there is little natural air flow thru radiator and the flex fan isn't pulling much air because it has flattened out due to the high engine rpm. You could easily have the same situation with your car running hot in slow traffic. The natural tendency is to rev up the engine to generate more flow from fan, THINK AGAIN. The only way this works is with a FIXED blade fan. If the fixed fan is mounted on a thermal fan clutch, it will help control fan speed by sensing the air temp. I ran my big block with a fixed 7 blade in order to deal with creeping cruise speeds. The problem was the fan howled at normal road speeds; but it sure did keep the temp gauge in check at low speeds.

[Bob S.]

Re: Trying to cool my 59 on hot summer days

Bill, that makes sense to me. I think where I get the benefit from the 5 blade flex fan is it produces more airflow than my standard 4 blade AT IDLE. You are right. I am guilty of giving it a little gas while at the light (in neutral, left foot on the brake and right on the gas).

That is where I was going with my original post. Corvette Central has a replacement 17", 6 blade fixed clutch fan that fits 61-70. To be able to use a clutch I would have to change my shroud to 1960 version. (That fan has the bolt pattern for a clutch and will not bolt directly to the water pump.) I have tried on my 59 and the clutch length puts the fan too far forward and it hits the shroud.

I think that will work but it also costs around $500 for parts. Soooo, I think I will spend $20 for a new VAC and invest some time and energy to exhaust the timing issue first.

[Duke W.]

Re: Trying to cool my 59 on hot summer days

Base cams should pull about 18" idling in neutral... maybe your cam is not a duplicate of the early or '67-up base cam. In any event, if idle vacuum is 15" @ 500 you need a B26 to pass the Two-Inch Rule, so got with the B26.

The ST-12 data converted to crank advance and degrees says the advance should start at about 700 engine RPM and provide a maximum of nominally provide 28 at 3700. The data for your distributor test indicates about 21-22 at 3700, so it doesn't meet spec, and some of the test data presented is confusing, so you need to get the guy to explain it.

Maybe the centrifugal springs are stiffer than OE, so if he revved it higher it would have achieved 28. The mechanism should be squeaky clean - no oil or grease... just wipe down the parts with WD-40 to provide a little corrosion protection.

Most OE centrifugal advance setups are "lazy", and improved performance can be had by bringing it all in at a lower RPM - somewhere around 3000 on a base engine. Initial timing recommendations are also often less than ideal. The whole spark advance map is overly conservative to protect the engine from detonation in extreme conditions because some people will drive a detonating engine until if fails, but vintage car guys should know better.

With 28 max centrifugal in order to achieve 36-40 total WOT advance, the initial should be in the range of 8-12, and with 15 degrees max vacuum advance total idle advance should be in the range of 25-28.

So what remains is to find out why your centrifugal is short and understand what the test data is actually saying because some of it is confusing or doesn't make any sense.

Duke

[Bob S.]

Re: Trying to cool my 59 on hot summer days

Thanks Duke. The VAC had to be ordered and will be in in the morning. In the meantime I am going to try to get the answer to our test data questions and do some experimenting with the current VAC.

[Frank D.]

Re: Trying to cool my 59 on hot summer days

I nearly lost a thumb to a flex fan when changing a radiator upper hose once when my hand slipped (engine NOT running)..cut meat and tendon to the bone. I wouldn't put one on my worst enemy's car.

I've seen advance mappings cure minor temp problems but not chronic, large overtemp issues. I'd be looking at that water pump...also IIRC there is a spring in that bottom radiator hose.....make sure that hose isn't collapsing when the car is running hot...

My original 270hp, dual quad solid lifter '61 will sit in the hot Florida summer heat at a stoplight for 10 minutes and never exceed 190*.
5-blade fan, NO fan clutch - pipe foam and rubber seals ALL around the radiator shroud. I replaced the original dual point distributor with one supporting a vacuum advance pulling full manifold vacuum at idle.

[Mark E.]

Re: Trying to cool my 59 on hot summer days

With 28 max centrifugal in order to achieve 36-40 total WOT advance, the initial should be in the range of 8-12, and with 15 degrees max vacuum advance total idle advance should be in the range of 25-28.

So what remains is to find out why your centrifugal is short and understand what the test data is actually saying because some of it is confusing or doesn't make any sense. Duke

I agree the mechanical and vacuum advance curves should be checked and sorted, but since the car only overheats while idling (correct?), only the timing at idle has a chance of fixing the immediate problem.

So once a VAC that passes the 2 inch rule is installed, it might be worthwhile to adjust (i.e. advance) the static timing at idle and see if that helps with the overheating problem.