[Vet65te]

Well, I drove over to one of the 'Test Only' Smog Stations figuring I'd pay the same $40 they charge for a loaded test but just get the guy to hook up and tell me the numbers but they aren't supposed to perform diagnostic testing so I brought it on home and hooked up my Gunson CO Tester. It's a relatively cheap outfit, a bit over $125 at least back when I bought it about ten years ago. Let it stabilize and zero it out, according to the instructions, to a reading of 2.0 and verify that it sits at that mark for at least two minutes afterwards and then plug it into the tailpipe and it is supposed to be ready within a minute or so. Stuck it in and the numbers started cliimbing. Garage temp was 70*, idle rpm at 750, engine temp between 180/185, initial timing at 14* plus another
12* from the vacuum advance pod. The digital readout kept climbing and climbing slowly till it reached 6.4 and stopped there. Hell, according to the chart, that means that the Air/Fuel ratio at idle is 12.09. That's rich, if I'm reading the chart correctly.
I'll wait for it to clear out and then try the same test at 2500 rpm.

[Hurst65]

Vet65te- just curious...what jets do you have in the carbs now?

Just for comparison sakes I'm running 72-68-72 jets. My plugs have very little color to them. I would love to know what mine shows on a machine while running but,.....maybe one day. I have my initial timimg at about 12 degrees.

I really can't see why your car is having problems. I mean you have a good rad., a shroud, you've set the clearance in the pump, you have a new fan clutch, plus you have an elec. fan. That should be more than enough. What else is there...????

[Vet65te]

Okay, just ran it for the minute and a half at a steady 2500 rpm. Not what I expected.
It slowly came up from 2.0 to about 2.4 and then settled for the longest time at 2.5 and basically stayed there for over a minute till I shut it down. So, the 2500 rpm CO reading of 2.5 comes out to an air/fuel reading of 13.55. So, it seems the idle CO should be quite a bit less and the higher rpm reading is either not too bad or maybe a bit lean?

One other observation while doing this testing with the hood up. At the idle rpm test, the engine stayed right around the low 180's with no climbing to be seen (Robert Shaw Thermo seems to open at about that mark). When running the car, again with the hood up, at the somewhat prolonged 2500 rpm mark, the temps started to climb up towards 200 when the electric fan came on.

I guess this 'entry level testing' I just performed sorta shoots the theory of running too lean all too hell.

Oh, Bronze66 did pass along to me the link for Stewart Components and in their tech tips section for Water Pumps and Pulleys, they recommended the following for street cars...For STREET applications, the water pump speed must at least match crankshaft RPM, to a maximum recommended 25% faster than crankshaft speed. My stock 64 crank pulley is 7-inches and the stock 64 water pump pulley is 8-inches. Looks like another reason to look for a smaller water pump pulley.

[LPete]

If you're saying it's reading 2.5% CO at 2500 RPM that's not lean -- if anything, it's a tad on the rich side, but I'd leave it. It's very rich at idle if it's at 6.4%. It should be more like 1 - 2%. It would also be interesting to know the loaded mixture, especially in power enrichment.

You probably know this, but at 14.7:1 (stoichiometric for gasoline) and leaner, CO is theoretically zero. A CO meter doesn't tell you anything when you're lean of stoich.

[Vet65te]

I just did a re-test at idle rpm and again, it came slowly up to 6.4/6.5 again. I might try to bring the idle mixture screws down a hair to see if I can get a response out of the little Gunson CO test unit but in the back of my mind, I'm still trying to figure out why I did see a rise in the vacuum reading back when I increased the setting from 1.5 to 1.75 and on up to 2.25. Also, with an idle richness this high I still can't figure out why the plugs look so white and the engine is still idling very smoothly...at least to the 'ear'.

[Hurst65]

I'm going to go out on a limb here but, I'll bet you an ice cold beer that if you go up a few sizes on the center jets it will cool down some at cruise speed.

Maybe not but, that's what I'm thinkin'.....

[LPete]

Originally Posted by Vet65te

I just did a re-test at idle rpm and again, it came slowly up to 6.4/6.5 again. I might try to bring the idle mixture screws down a hair to see if I can get a response out of the little Gunson CO test unit but in the back of my mind, I'm still trying to figure out why I did see a rise in the vacuum reading back when I increased the setting from 1.5 to 1.75 and on up to 2.25. Also, with an idle richness this high I still can't figure out why the plugs look so white and the engine is still idling very smoothly...at least to the 'ear'.

Engines run great on a rich mixture, they just pollute a lot. I've seen them run at 10% CO and idle perfectly. I still don't believe plug color is a good indicator of idle mixture.

As you slowly turn the mixture screws in, you'll notice a point where the idle speed drops drastically with very little movement of the screws. That point is very close to 14.7:1. Leaner than that, and it won't run. Richer, and it mostly just produces more CO, although it can smooth out a bit due to mixture variation between cylinders.

[Vet65te]

Just finished running the CO tester with the engine idling 'after' turning the mixture screws in a 1/4-turn, from 2.25 down to 2.00. No apparent change of idle rpm, no change in vacuum reading which was a bit under 18 and steady at 750 rpm.
The CO tester now reads 4.7 CO instead of the 6.4/6.5 I got earlier. I realize that means the A/F ratio at idle is still a fat 12.74 but I think I'll leave it at that point for now till I get more miles on it. Still a puzzler alright. I still have the 16-inch electric fan as my safety net for those times I get stuck at lights or the daytime temps are high but until I get a good thousand miles on it, I'll probably hold off on anymore adjustments.
I will, however, continue to snoop around for a 7-inch diameter water pump pulley in order to crank up the water pump speed and fan speed.

Hurst65 - Can't recall the exact numbers off the top of my head but do remember when I rebuilt the carbs that they were the original jet sizes.

Thanks to all for the input and assistance, there's a cold beer waiting for any of you who happen to make it to Northern California.

[Vet65te]

Before this thread fades away, I wanted to ask if anyone has figured out a relatively simple way to seal off the aftermarket fan shroud. My '64 never had a shroud but I added one and found that there's quite a bit of 'gap-itis' at the top and top corners.
Short of fabing one up via cardboard templates, has anyone found something to plug the irregular openings that these shrouds have?
Thanks

[Dick Boneske]

I've gone through this same thing a few times through the years with Pontiac engines. First, let me comment on some things you've tried and my experience with them.

As you stated in your OP, the engine is freshly rebuilt and tight. I don't know if you used a rope seal for the rear mains, but this alone on Pontiac engines adds a huge amount of friction. Ditto for new piston rings. Synthetic oil with a zinc-rich supplement for the cam & lifters will lower the temp immedately. When I experienced what you've described, I just drove the car and avoided extended idling until I racked up some miles.

Second, I'm puzzled as to why you run a 180 degree thermostat on this newly rebuilt engine. Why not a 160 degree--at least until you get 500 or so miles on the engine? I always run 160 degree thermostats in old Pontiacs in summer.

Third, why run an electric fan that turns on at 200 degrees? Why don't you wire it so you can turn it on manually at idle?

Fourth, in 1964 when I bought my first GTO, it came from the factory with 3.90 gears, four core radiator, no shroud, and it NEVER overheated--even when I drove it home from the showroom. So, it's not the fan shroud or water pump pulley.

And last, the camshaft. These cars were built with relatively mild cams by today's standards. The cam you've chosen, while relatively mild, is not also relatively mild, but the added overlap compared to stock makes a lot of heat at idle due to the wasted fuel/air mixture not contibuting to running the engine.

I will venture to say the problem is not air/fuel mixture, water pump pulley size, or poorly sealed fan shroud. Main contibutors are the non-stock cam, 180 degree thermostat, and three core radiator vs. a four core the factory put in with all performance engine options.

[Vet65te]

Hello Dick, haven't talked with you in a while. The 3x2 Fuel Line parts I bought from you last year worked out fine.
As you've no doubt read, there have been a number of 'suspects' in this overheating issue I have and most of those suspects have been 'cleared' or dismissed.
Even though my posts are a bit wordy, I usually leave out something so let me fill in a few things and also respond to your observations.

I didn't use the rope seal. Instead I tried the new BOP Viton Rear Main Seal and it's been dry as a bone.

Since a thermostat only controls the low limit of engine temps I can't blame the 180 that's in there for the overheating issues. I used to always put the lowest one I could find (160) in all the Chevy engines I've built but did run across a couple of them that ran so darn cold-hearted that I had to move up to the 180. One smallblock, one Bigblock, and both would hover in the high 150's to about 162 with the 160 thermo. This engine slowly but surely get's warmer and warmer and when just idling in the driveway (and not much airflow which I'll talk about later) and will continue up to 200 and 210 and I know I haven't found the high limit yet so the the thermostat is just along for the ride in my particular case.
Also, I can't say I've seen any difference between the cheaper thermostat (also 180) versus the higher cost Robert Shaw thermostat other than the fact that the cheapo opened at around 178 and the RS opens in the 184/185 range (water pump to diverter plate mod performed as well with no noticeable difference).

Camshaft - That's true that the one I picked is considered mild and with 3:23 gears and my expected street driving that's what I wanted. Other than having a bit more lift, it's pretty close to the #068 cam that came out in later years.

Synthetic Oil - I think the general consensus is that synthetic oil does have plusses but in small percentage points. Also, most recommendations I've come across are to use non-synthetic oils for breakin periods and then switch. I know some people think the engine has broken in by the first 100 miles but I sorta lean towards more than that, say a thousand or two so I will make the switch but not quite yet. For now, I'm using the earlier version of 10-40 Rotella-T with ZDDP and even gave it a dose of STP.

Electric Fan - In an earlier posting regarding fan controllers, I blasted the good folks at BeCool since their controller did not perform as advertised. The adjustable device(s) I bought (3 for different cars but the GTO was the first to get one) were supposed to be able to activate the fan at 160/165 degrees. Not a chance. The lowest setting, on all three units by the way, was at the 195/200 mark. I even had to move the probe from their originally suggested location of center of the core, down a few inches from the top tank, to immediately below the inlet tube on the passenger side. I would like to have it come on earlier and will have to find another manufacturers device for fan activation but for now, I can live with the 16-inch, 18-amp, DeRale fan coming on just before 200. When it does fire off, it halts the temperature increase.

Air/Fuel Mixture Settings - On this one, it's a good thing I didn't bet any money. I would have lost big time. I've had some very clean running engines, but none of them produced plugs that were this clean and this 'bright white', at least in such a new engine. I could have sworn that a lean condition existed...although the fact that the vacuum reading was good and steady contradicted the notion of leanness.

Radiators - On this one, I have a question. When I bought the car in '94, it had a three row core. When I had it recored, they replaced it with the same size that was in there.
On non-A/C cars, was the standard radiator a 3-row or 4-row type?
Also, on the subject of radiators, I see the Pontiac engineers finally figured out in later years that they should put the inlet tube on one side and the outlet tube on the other but '64's and I think '65's had them on the same passenger side, swell, great design.

I couldn't agree more that these 'fixes' like electric fan, smaller water pump pulley and additional shroud sealing shouldn't be necessary...but, if I want to drive this car without fear of overheating somewhere out on the road, I have to try them.

I've owned the car since '94 but with all the other projects, and commuting 125 miles a day till I retired two years ago, it typically takes me a long time to get those miles on it to hopefully break it in. Looks like I will need to plan a few trips coming up.

[Hurst65]

Hey Vet,

Could you post some pics of that fan shroud???
That's one of the things next on my list.
Where did you get it? How much?

Thanks
Eric

[Vet65te]

Hurst, I bought the 64-67 non-A/C Shroud from Year One back in '97 and it was about $90 at the time. Here are some shots of the shroud. It took me a while to figure out how to use Photobucket but I haven't yet figured out how to downsize the shots so they seem to take up a bunch of room. The fit of the shroud is okay but nothing great.
It almost seems like the forward side opening should be a bit bigger as you'll notice that the core seems higher than it should be for this shroud. I had to use a short spacer to push the fan a bit more forward and it's just inside the shroud at the top and half way in at the bottom. Also, there's no more than a 1/2-inch of gap between the blades at 6-o'clock and the shroud so that's why I was unable to push it upwards.

[Hurst65]

That's interesting..... are the 64 and 65 fans different???
On my fan the blades are shaped different. On mine the blades are more squared off looking. It looks like the blades on mine have much more blade area. The front edge of the blade is rounded off some but, not near as much as what you have.

I see what you mean by the shroud not fitting very well. That gap between the fan blades and the shroud at the 12 o'clock position is huge. That does not seem right to me. I've seen other repop shrouds on a couple people's car and there was a slight gap between the shroud and the rad. along the sides and some at the top but, the fan fit well with the shroud. Something you may want to look into...?? In order for that shroud to do it's job like its supposed to it should fit alot better than that.

[Hurst65]

Does the top of the shroud rub against the tubes???

[440GP69]

that shroud is way to far away from the fan, does it cool down when you are out cruising around and then when you stop does it get hotter and hotter? also i quit using thermostats in most of my engines, its not going to caus problems unless its a faulty thermostat 180 is too high if you are going to run one IMO 160-170 preferebly none at all.

[Vet65te]

The shroud stands off the core by about 3/16-1/4-inch. It doesn't touch. Pics sometimes give a skewed perspective of the proximity. As for whether the 7-blade fan is original, I'd guess that it is but remember, this is my first Pontiac and I bought it back in '94. Could have been a few changes made in the 30 years between the Fremont Manufacturing Plant and my purchase. The car had no shroud when I bought it, installing the shroud was just another case of 'more is better' that I sorta lean towards.
Even with the less than 'stellar' fit, I think the shroud does assist the air flow. Maybe not by a whole bunch but I do think it helps. One thing I'm pretty sure of and that is, it's not contributing to the overheating issue.

One other variable has come up recently and that's the fan clutch. I wrote early on that the so-called heavy duty version was no longer in production and that I've used two different brands of clutch units. You might have seen some writeups in the past about 'tweaking' the clutch unit by rotating the external spring up front (if you don't have the plate type) and that by doing that little mod, the lockup occurs earlier.
I've tried this once before many moons ago on a Corvette and saw no difference.
I just might try it this time too but for now, I'm back to racking up more miles to hopefully lessen the ring friction that I think is responsible for most of the overheating.

So, got pics of your 65's fan setup?

[Hurst65]

Here's a picture of mine.

[Old Man Taylor]

I don't know that it is your problem, but your fan is too far behind the shroud.

[Vet65te]

Hurst65 - I looked up the repro fan blades available from Performance Years and they have one 7-blade fan that looks very similar to the one I have in my '64, RPE67, and it's got the 'curled blade ends'. Like I said, I expected that mine was the stocker only because it has the aluminum blades and I've never seen any Chevy with anything but steel blade fans...but it could be non-original after all.

What size is your radiator? Back when I had mine recored, we went with a one-for-one replacement for the 3-row copper/brass unit that was in there. If this overheating persists beyond a thousand miles I might consider replacing it with an aluminum version but also try to reconfigure things so it's not like the poorly designed original tripower setup where the inlet and outlet tubes are on the same side of the radiator.

As for the shroud, I looked through the Year One listings and found the one I bought and it's a F93 for 64-67 Non-A/C and Performance Years has one that's similar (and cheaper) listed as RPE67P which is listed as 65-67 w/AC and all 64's. It looks to be identical to the one I have but I suspect the fan blade opening is a bit larger. Non of them seem to be a great fit but I do think they are better than going without one.